Table of Contents ***************** GNU M4 1 Introduction and preliminaries 1.1 Introduction to `m4' 1.2 Historical references 1.3 Invoking `m4' 1.4 Problems and bugs 1.5 Using this manual 2 Lexical and syntactic conventions 2.1 Macro names 2.2 Quoting input to `m4' 2.3 Comments in `m4' input 2.4 Other kinds of input tokens 2.5 How `m4' copies input to output 3 How to invoke macros 3.1 Macro invocation 3.2 Preventing macro invocation 3.3 Macro arguments 3.4 On Quoting Arguments to macros 3.5 Macro expansion 4 How to define new macros 4.1 Defining a macro 4.2 Arguments to macros 4.3 Special arguments to macros 4.4 Deleting a macro 4.5 Renaming macros 4.6 Temporarily redefining macros 4.7 Indirect call of macros 4.8 Indirect call of builtins 5 Conditionals, loops, and recursion 5.1 Testing if a macro is defined 5.2 If-else construct, or multibranch 5.3 Loops and recursion 6 How to debug macros and input 6.1 Displaying macro definitions 6.2 Tracing macro calls 6.3 Controlling debugging output 6.4 Saving debugging output 7 Input control 7.1 Deleting whitespace in input 7.2 Changing the quote characters 7.3 Changing the comment delimiters 7.4 Changing the lexical structure of words 7.5 Saving text until end of input 8 File inclusion 8.1 Including named files 8.2 Searching for include files 9 Diverting and undiverting output 9.1 Diverting output 9.2 Undiverting output 9.3 Diversion numbers 9.4 Discarding diverted text 10 Macros for text handling 10.1 Calculating length of strings 10.2 Searching for substrings 10.3 Searching for regular expressions 10.4 Extracting substrings 10.5 Translating characters 10.6 Substituting text by regular expression 10.7 Formatted output 11 Macros for doing arithmetic 11.1 Decrement and increment operators 11.2 Evaluating integer expressions 12 Macros for running shell commands 12.1 Determining the platform 12.2 Executing simple commands 12.3 Reading the output of commands 12.4 Exit status 12.5 Making temporary files 13 Miscellaneous builtin macros 13.1 Printing error messages 13.2 Printing current location 13.3 Exiting from `m4' 14 Fast loading of frozen state 14.1 Using frozen files 14.2 Frozen file format 15 Compatibility with other versions of `m4' 15.1 Extensions in GNU `m4' 15.2 Facilities in System V `m4' not in GNU `m4' 15.3 Other incompatibilities 16 Correct version of some examples Appendix A How to make copies of this manual A.1 GNU Free Documentation License Appendix B Indices of concepts and macros B.1 Index for many concepts B.2 Index for all `m4' macros GNU M4 ****** This manual is for GNU M4 (version 1.4.7, 23 September 2006), a package containing an implementation of the m4 macro language. Copyright (C) 1989, 1990, 1991, 1992, 1993, 1994, 2004, 2005, 2006 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License." GNU `m4' is an implementation of the traditional UNIX macro processor. It is mostly SVR4 compatible, although it has some extensions (for example, handling more than 9 positional parameters to macros). `m4' also has builtin functions for including files, running shell commands, doing arithmetic, etc. Autoconf needs GNU `m4' for generating `configure' scripts, but not for running them. GNU `m4' was originally written by Rene' Seindal, with subsequent changes by Franc,ois Pinard and other volunteers on the Internet. All names and email addresses can be found in the files `AUTHORS' and `THANKS' from the GNU M4 distribution. This is release 1.4.7. It is now considered stable: future releases in the 1.4.x series are only meant to fix bugs, increase speed, or improve documentation. However... An experimental feature, which would improve `m4' usefulness, allows for changing the syntax for what is a "word" in `m4'. You should use: ./configure --enable-changeword if you want this feature compiled in. The current implementation slows down `m4' considerably and is hardly acceptable. In the future, `m4' 2.0 will come with a different set of new features that provide similar capabilities, but without the inefficiencies, so changeword will go away and _you should not count on it_. 1 Introduction and preliminaries ******************************** This first chapter explains what GNU `m4' is, where `m4' comes from, how to read and use this documentation, how to call the `m4' program, and how to report bugs about it. It concludes by giving tips for reading the remainder of the manual. The following chapters then detail all the features of the `m4' language. 1.1 Introduction to `m4' ======================== `m4' is a macro processor, in the sense that it copies its input to the output, expanding macros as it goes. Macros are either builtin or user-defined, and can take any number of arguments. Besides just doing macro expansion, `m4' has builtin functions for including named files, running shell commands, doing integer arithmetic, manipulating text in various ways, performing recursion, etc.... `m4' can be used either as a front-end to a compiler, or as a macro processor in its own right. The `m4' macro processor is widely available on all UNIXes, and has been standardized by POSIX. Usually, only a small percentage of users are aware of its existence. However, those who find it often become committed users. The popularity of GNU Autoconf, which requires GNU `m4' for _generating_ `configure' scripts, is an incentive for many to install it, while these people will not themselves program in `m4'. GNU `m4' is mostly compatible with the System V, Release 3 version, except for some minor differences. *Note Compatibility::, for more details. Some people find `m4' to be fairly addictive. They first use `m4' for simple problems, then take bigger and bigger challenges, learning how to write complex sets of `m4' macros along the way. Once really addicted, users pursue writing of sophisticated `m4' applications even to solve simple problems, devoting more time debugging their `m4' scripts than doing real work. Beware that `m4' may be dangerous for the health of compulsive programmers. 1.2 Historical references ========================= `GPM' was an important ancestor of `m4'. See C. Stratchey: "A General Purpose Macro generator", Computer Journal 8,3 (1965), pp. 225 ff. `GPM' is also succinctly described into David Gries classic "Compiler Construction for Digital Computers". The classic B. Kernighan and P.J. Plauger: "Software Tools", Addison-Wesley, Inc. (1976) describes and implements a Unix macro-processor language, which inspired Dennis Ritchie to write `m3', a macro processor for the AP-3 minicomputer. Kernighan and Ritchie then joined forces to develop the original `m4', as described in "The M4 Macro Processor", Bell Laboratories (1977). It had only 21 builtin macros. While `GPM' was more _pure_, `m4' is meant to deal with the true intricacies of real life: macros can be recognized without being pre-announced, skipping whitespace or end-of-lines is easier, more constructs are builtin instead of derived, etc. Originally, the Kernighan and Plauger macro-processor, and then `m3', formed the engine for the Rational FORTRAN preprocessor, that is, the `Ratfor' equivalent of `cpp'. Later, `m4' was used as a frontend for `Ratfor', `C' and `Cobol'. Rene' Seindal released his implementation of `m4', GNU `m4', in 1990, with the aim of removing the artificial limitations in many of the traditional `m4' implementations, such as maximum line length, macro size, or number of macros. The late Professor A. Dain Samples described and implemented a further evolution in the form of `M5': "User's Guide to the M5 Macro Language: 2nd edition", Electronic Announcement on comp.compilers newsgroup (1992). Franc,ois Pinard took over maintenance of GNU `m4' in 1992, until 1994 when he released GNU `m4' 1.4, which was the stable release for 10 years. It was at this time that GNU Autoconf decided to require GNU `m4' as its underlying engine, since all other implementations of `m4' had too many limitations. More recently, in 2004, Paul Eggert released 1.4.1 and 1.4.2 which addressed some long standing bugs in the venerable 1.4 release. Then in 2005 Gary V. Vaughan collected together the many patches to GNU `m4' 1.4 that were floating around the net and released 1.4.3 and 1.4.4. And in 2006, Eric Blake joined the team and prepared patches for the release of 1.4.5, 1.4.6, and 1.4.7. Meanwhile, development has continued on new features for `m4', such as dynamic module loading and additional builtins. When complete, GNU `m4' 2.0 will start a new series of releases. 1.3 Invoking `m4' ================= The format of the `m4' command is: `m4' [OPTION...] [FILE...] All options begin with `-', or if long option names are used, with `--'. A long option name need not be written completely, any unambiguous prefix is sufficient. Unless `POSIXLY_CORRECT' is set in the environment, options may be intermixed with files. The argument `--' is a marker to denote the end of options. With short options, options that do not take arguments may be combined into a single command line argument with subsequent options, options with mandatory arguments may be provided either as a single command line argument or as two arguments, and options with optional arguments must be provided as a single argument. In other words, without `POSIXLY_CORRECT', `m4 -QPDfoo -d a -d+f' is equivalent to `m4 -Q -P -D foo -d -d+f -- a', although the latter form is considered canonical. (With `POSIXLY_CORRECT', it is equivalent to `m4 -Q -P -D foo -d -- a ./-d+f'). With long options, options with mandatory arguments may be provided with an equal sign (`=') in a single argument, or as two arguments, and options with optional arguments must be provided as a single argument. In other words, `m4 --def foo --debug a' is equivalent to `m4 --define=foo --debug= -- a', although the latter form is considered canonical (not to mention more robust, in case a future version of `m4' introduces an option named `--default'). `m4' understands the following options, grouped by functionality. Several options control the overall operation of `m4': `--help' Print a help summary on standard output, then immediately exit `m4' without reading any input files. `--version' Print the version number of the program on standard output, then immediately exit `m4' without reading any input files. `-E' `--fatal-warnings' Stop execution and exit `m4' once the first warning has been issued, considering all of them to be fatal. `-i' `--interactive' `-e' Makes this invocation of `m4' interactive. This means that all output will be unbuffered, and interrupts will be ignored. The spelling `-e' exists for compatibility with other `m4' implementations, and issues a warning because it may be withdrawn in a future version of GNU M4. `-P' `--prefix-builtins' Internally modify _all_ builtin macro names so they all start with the prefix `m4_'. For example, using this option, one should write `m4_define' instead of `define', and `m4___file__' instead of `__file__'. This option has no effect if `-R' is also specified. `-Q' `--quiet' `--silent' Suppress warnings, such as missing or superfluous arguments in macro calls, or treating the empty string as zero. `-W REGEXP' `--word-regexp=REGEXP' Use REGEXP as an alternative syntax for macro names. This experimental option will not be present on all GNU `m4' implementations (*note Changeword::). Several options allow `m4' to behave more like a preprocessor. Macro definitions and deletions can be made on the command line, the search path can be altered, and the output file can track where the input came from. These features occur with the following options: `-D NAME[=VALUE]' `--define=NAME[=VALUE]' This enters NAME into the symbol table, before any input files are read. If `=VALUE' is missing, the value is taken to be the empty string. The VALUE can be any string, and the macro can be defined to take arguments, just as if it was defined from within the input. This option may be given more than once; order is significant, and redefining the same NAME loses the previous value. `-I DIRECTORY' `--include=DIRECTORY' Make `m4' search DIRECTORY for included files that are not found in the current working directory. *Note Search Path::, for more details. This option may be given more than once. `-s' `--synclines' Generate synchronization lines, for use by the C preprocessor or other similar tools. This is useful, for example, when `m4' is used as a front end to a compiler. Source file name and line number information is conveyed by directives of the form `#line LINENUM "FILE"', which are inserted as needed into the middle of the output. Such directives mean that the following line originated or was expanded from the contents of input file FILE at line LINENUM. The `"FILE"' part is often omitted when the file name did not change from the previous directive. Synchronization directives are always given on complete lines by themselves. When a synchronization discrepancy occurs in the middle of an output line, the associated synchronization directive is delayed until the beginning of the next generated line. `-U NAME' `--undefine=NAME' This deletes any predefined meaning NAME might have. Obviously, only predefined macros can be deleted in this way. This option may be given more than once; undefining a NAME that does not have a definition is silently ignored. There are some limits within `m4' that can be tuned. For compatibility, `m4' also accepts some options that control limits in other implementations, but which are automatically unbounded (limited only by your hardware constraints) in GNU `m4'. `-G' `--traditional' Suppress all the extensions made in this implementation, compared to the System V version. *Note Compatibility::, for a list of these. `-H NUM' `--hashsize=NUM' Make the internal hash table for symbol lookup be NUM entries big. For better performance, the number should be prime, but this is not checked. The default is 509 entries. It should not be necessary to increase this value, unless you define an excessive number of macros. `-L NUM' `--nesting-limit=NUM' Artificially limit the nesting of macro calls to NUM levels, stopping program execution if this limit is ever exceeded. When not specified, nesting is limited to 1024 levels. The precise effect of this option might be more correctly associated with textual nesting than dynamic recursion. It has been useful when some complex `m4' input was generated by mechanical means. Most users would never need this option. If shown to be obtrusive, this option (which is still experimental) might well disappear. This option does _not_ have the ability to break endless rescanning loops, since these do not necessarily consume much memory or stack space. Through clever usage of rescanning loops, one can request complex, time-consuming computations from `m4' with useful results. Putting limitations in this area would break `m4' power. There are many pathological cases: `define(`a', `a')a' is only the simplest example (but *note Compatibility::). Expecting GNU `m4' to detect these would be a little like expecting a compiler system to detect and diagnose endless loops: it is a quite _hard_ problem in general, if not undecidable! `-B NUM' `-S NUM' `-T NUM' These options are present for compatibility with System V `m4', but do nothing in this implementation. They may disappear in future releases, and issue a warning to that effect. `-N NUM' `--diversions=NUM' These options are present only for compatibility with previous versions of GNU `m4', and were controlling the number of possible diversions which could be used at the same time. They do nothing, because there is no fixed limit anymore. They may disappear in future releases, and issue a warning to that effect. GNU `m4' comes with a feature of freezing internal state (*note Frozen files::). This can be used to speed up `m4' execution when reusing a common initialization script. `-F FILE' `--freeze-state=FILE' Once execution is finished, write out the frozen state on the specified FILE. It is conventional, but not required, for FILE to end in `.m4f'. `-R FILE' `--reload-state=FILE' Before execution starts, recover the internal state from the specified frozen FILE. The options `-D', `-U', and `-t' take effect after state is reloaded, but before the input files are read. Finally, there are several options for aiding in debugging `m4' scripts. `-d[FLAGS]' `--debug[=FLAGS]' Set the debug-level according to the flags FLAGS. The debug-level controls the format and amount of information presented by the debugging functions. *Note Debug Levels::, for more details on the format and meaning of FLAGS. If omitted, FLAGS defaults to `aeq'. `--debugfile=FILE' `-o FILE' `--error-output=FILE' Redirect `dumpdef' output, debug messages, and trace output to the named FILE. Warnings, error messages, and `errprint' output are still printed to standard error. If unspecified, debug output goes to standard error; if empty, debug output is discarded. *Note Debug Output::, for more details. The spellings `-o' and `--error-output' are misleading and inconsistent with other GNU tools; for now they are silently accepted as synonyms of `--debugfile', but in a future version of M4, using them will cause a warning to be issued. `-l NUM' `--arglength=NUM' Restrict the size of the output generated by macro tracing to NUM characters per trace line. If unspecified or zero, output is unlimited. *Note Debug Levels::, for more details. `-t NAME' `--trace=NAME' This enables tracing for the macro NAME, at any point where it is defined. NAME need not be defined when this option is given. This option may be given more than once. *Note Trace::, for more details. The remaining arguments on the command line are taken to be input file names. If no names are present, the standard input is read. A file name of `-' is taken to mean the standard input. It is conventional, but not required, for input files to end in `.m4'. The input files are read in the sequence given. Standard input can be read more than once, so the file name `-' may appear multiple times on the command line; this makes a difference when input is from a terminal or other special file type. It is an error if an input file ends in the middle of argument collection, a comment, or a quoted string. If none of the input files invoked `m4exit' (*note M4exit::), the exit status of `m4' will be 0 for success, 1 for general failure (such as problems with reading an input file), and 63 for version mismatch (*note Using frozen files::). If you need to read a file whose name starts with a `-', you can specify it as `./-file', or use `--' to mark the end of options. 1.4 Problems and bugs ===================== If you have problems with GNU M4 or think you've found a bug, please report it. Before reporting a bug, make sure you've actually found a real bug. Carefully reread the documentation and see if it really says you can do what you're trying to do. If it's not clear whether you should be able to do something or not, report that too; it's a bug in the documentation! Before reporting a bug or trying to fix it yourself, try to isolate it to the smallest possible input file that reproduces the problem. Then send us the input file and the exact results `m4' gave you. Also say what you expected to occur; this will help us decide whether the problem was really in the documentation. Once you've got a precise problem, send e-mail to (Internet) . Please include the version number of `m4' you are using. You can get this information with the command `m4 --version'. Also provide details about the platform you are executing on. Non-bug suggestions are always welcome as well. If you have questions about things that are unclear in the documentation or are just obscure features, please report them too. 1.5 Using this manual ===================== This manual contains a number of examples of `m4' input and output, and a simple notation is used to distinguish input, output and error messages from `m4'. Examples are set out from the normal text, and shown in a fixed width font, like this This is an example of an example! To distinguish input from output, all output from `m4' is prefixed by the string `=>', and all error messages by the string `error-->'. Thus Example of input line =>Output line from m4 error-->and an error message The sequence `^D' in an example indicates the end of the input file. The majority of these examples are self-contained, and you can run them with similar results by invoking `m4 -d'. In fact, the testsuite that is bundled in the GNU M4 package consists of the examples in this document! As each of the predefined macros in `m4' is described, a prototype call of the macro will be shown, giving descriptive names to the arguments, e.g., -- Composite: example (STRING, [COUNT = `1'], [ARGUMENT]...) This is a sample prototype. There is not really a macro named `example', but this documents that if there were, it would be a Composite macro, rather than a Builtin. It requires at least one argument, STRING. Remember that in `m4', there must not be a space between the macro name and the opening parenthesis, unless it was intended to call the macro without any arguments. The brackets around COUNT and ARGUMENT show that these arguments are optional. If COUNT is omitted, the macro behaves as if count were `1', whereas if ARGUMENT is omitted, the macro behaves as if it were the empty string. A blank argument is not the same as an omitted argument. For example, `example(`a')', `example(`a',`1')', and `example(`a',`1',)' would behave identically with COUNT set to `1'; while `example(`a',)' and `example(`a',`')' would explicitly pass the empty string for COUNT. The ellipses (`...') show that the macro processes additional arguments after ARGUMENT, rather than ignoring them. All macro arguments in `m4' are strings, but some are given special interpretation, e.g., as numbers, file names, regular expressions, etc. The documentation for each macro will state how the parameters are interpreted, and what happens if the argument cannot be parsed according to the desired interpretation. Unless specified otherwise, a parameter specified to be a number is parsed as a decimal, even if the argument has leading zeros; and parsing the empty string as a number results in 0 rather than an error, although a warning will be issued. This document consistently writes and uses "builtin", without a hyphen, as if it were an English word. This is how the `builtin' primitive is spelled within `m4'. 2 Lexical and syntactic conventions *********************************** As `m4' reads its input, it separates it into "tokens". A token is either a name, a quoted string, or any single character, that is not a part of either a name or a string. Input to `m4' can also contain comments. GNU `m4' does not yet understand locales; all operations are byte-oriented rather than character-oriented. However, `m4' is eight-bit clean, so you can use non-ASCII characters in quoted strings (*note Changequote::), comments (*note Changecom::), and macro names (*note Indir::), with the exception of the NUL character (the zero byte `'\0''). 2.1 Macro names =============== A name is any sequence of letters, digits, and the character `_' (underscore), where the first character is not a digit. `m4' will use the longest such sequence found in the input. If a name has a macro definition, it will be subject to macro expansion (*note Macros::). Names are case-sensitive. Examples of legal names are: `foo', `_tmp', and `name01'. 2.2 Quoting input to `m4' ========================= A quoted string is a sequence of characters surrounded by quote strings, defaulting to ``' and `'', where the nested begin and end quotes within the string are balanced. The value of a string token is the text, with one level of quotes stripped off. Thus `' => is the empty string, and double-quoting turns into single-quoting. ``quoted'' =>`quoted' The quote characters can be changed at any time, using the builtin macro `changequote'. *Note Changequote::, for more information. 2.3 Comments in `m4' input ========================== Comments in `m4' are normally delimited by the characters `#' and newline. All characters between the comment delimiters are ignored, but the entire comment (including the delimiters) is passed through to the output--comments are _not_ discarded by `m4'. Comments cannot be nested, so the first newline after a `#' ends the comment. The commenting effect of the begin-comment string can be inhibited by quoting it. `quoted text' # `commented text' =>quoted text # `commented text' `quoting inhibits' `#' `comments' =>quoting inhibits # comments The comment delimiters can be changed to any string at any time, using the builtin macro `changecom'. *Note Changecom::, for more information. 2.4 Other kinds of input tokens =============================== Any character, that is neither a part of a name, nor of a quoted string, nor a comment, is a token by itself. When not in the context of macro expansion, all of these tokens are just copied to output. However, during macro expansion, whitespace characters (space, tab, newline, formfeed, carriage return, vertical tab), parentheses (`(' and `)'), comma (`,'), and dollar (`$') have additional roles, explained later. 2.5 How `m4' copies input to output =================================== As `m4' reads the input token by token, it will copy each token directly to the output immediately. The exception is when it finds a word with a macro definition. In that case `m4' will calculate the macro's expansion, possibly reading more input to get the arguments. It then inserts the expansion in front of the remaining input. In other words, the resulting text from a macro call will be read and parsed into tokens again. `m4' expands a macro as soon as possible. If it finds a macro call when collecting the arguments to another, it will expand the second call first. For a running example, examine how `m4' handles this input: format(`Result is %d', eval(`2**15')) First, `m4' sees that the token `format' is a macro name, so it collects the tokens `(', ``Result is %d'', `,', and ` ', before encountering another potential macro. Sure enough, `eval' is a macro name, so the nested argument collection picks up `(', ``2**15'', and `)', invoking the eval macro with the lone argument of `2**15'. The expansion of `eval(2**15)' is `32768', which is then rescanned as the five tokens `3', `2', `7', `6', and `8'; and combined with the next `)', the format macro now has all its arguments, as if the user had typed: format(`Result is %d', 32768) The format macro expands to `Result is 32768', and we have another round of scanning for the tokens `Result', ` ', `is', ` ', `3', `2', `7', `6', and `8'. None of these are macros, so the final output is =>Result is 32768 The order in which `m4' expands the macros can be explored using the *Note Trace:: facilities of GNU `m4'. This process continues until there are no more macro calls to expand and all the input has been consumed. 3 How to invoke macros ********************** This chapter covers macro invocation, macro arguments and how macro expansion is treated. 3.1 Macro invocation ==================== Macro invocations has one of the forms name which is a macro invocation without any arguments, or name(arg1, arg2, ..., argN) which is a macro invocation with N arguments. Macros can have any number of arguments. All arguments are strings, but different macros might interpret the arguments in different ways. The opening parenthesis _must_ follow the NAME directly, with no spaces in between. If it does not, the macro is called with no arguments at all. For a macro call to have no arguments, the parentheses _must_ be left out. The macro call name() is a macro call with one argument, which is the empty string, not a call with no arguments. 3.2 Preventing macro invocation =============================== An innovation of the `m4' language, compared to some of its predecessors (like Stratchey's `GPM', for example), is the ability to recognize macro calls without resorting to any special, prefixed invocation character. While generally useful, this feature might sometimes be the source of spurious, unwanted macro calls. So, GNU `m4' offers several mechanisms or techniques for inhibiting the recognition of names as macro calls. First of all, many builtin macros cannot meaningfully be called without arguments. For any of these macros, whenever an opening parenthesis does not immediately follow their name, the builtin macro call is not triggered. This solves the most usual cases, like for `include' or `eval'. Later in this document, the sentence "This macro is recognized only with parameters" refers to this specific provision. There is also a command line option (`--prefix-builtins', or `-P', *note Invoking m4::) that renames all builtin macro with a prefix of `m4_' at startup. The option has no effect whatsoever on user defined macros. For example, with this option, one has to write `m4_dnl' and even `m4_m4exit'. It also has no effect on whether a macro requires parameters. Another alternative is to redefine problematic macros to a name less likely to cause conflicts, *Note Definitions::. If your version of GNU `m4' has the `changeword' feature compiled in, it offers far more flexibility in specifying the syntax of macro names, both builtin or user-defined. *Note Changeword::, for more information on this experimental feature. Of course, the simplest way to prevent a name from being interpreted as a call to an existing macro is to quote it. The remainder of this section studies a little more deeply how quoting affects macro invocation, and how quoting can be used to inhibit macro invocation. Even if quoting is usually done over the whole macro name, it can also be done over only a few characters of this name (provided, of course, that the unquoted portions are not also a macro). It is also possible to quote the empty string, but this works only _inside_ the name. For example: `divert' =>divert `d'ivert =>divert di`ver't =>divert div`'ert =>divert all yield the string `divert'. While in both: `'divert => divert`' => the `divert' builtin macro will be called, which expands to the empty string. The output of macro evaluations is always rescanned. The following example would yield the string `de', exactly as if `m4' has been given `substr(`abcde', `3', `2')' as input: define(`x', `substr(ab') => define(`y', `cde, `3', `2')') => x`'y =>de Unquoted strings on either side of a quoted string are subject to being recognized as macro names. In the following example, quoting the empty string allows for the second `macro' to be recognized as such: define(`macro', `m') => macro(`m')macro =>mmacro macro(`m')`'macro =>mm Quoting may prevent recognizing as a macro name the concatenation of a macro expansion with the surrounding characters. In this example: define(`macro', `di$1') => macro(`v')`ert' =>divert macro(`v')ert => the input will produce the string `divert'. When the quotes were removed, the `divert' builtin was called instead. 3.3 Macro arguments =================== When a name is seen, and it has a macro definition, it will be expanded as a macro. If the name is followed by an opening parenthesis, the arguments will be collected before the macro is called. If too few arguments are supplied, the missing arguments are taken to be the empty string. However, some builtins are documented to behave differently for a missing optional argument than for an explicit empty string. If there are too many arguments, the excess arguments are ignored. Unquoted leading whitespace is stripped off all arguments. Normally `m4' will issue warnings if a builtin macro is called with an inappropriate number of arguments, but it can be suppressed with the `--quiet' command line option (or `--silent', or `-Q', *note Invoking m4::). For user defined macros, there is no check of the number of arguments given. Macros are expanded normally during argument collection, and whatever commas, quotes and parentheses that might show up in the resulting expanded text will serve to define the arguments as well. Thus, if FOO expands to `, b, c', the macro call bar(a foo, d) is a macro call with four arguments, which are `a ', `b', `c' and `d'. To understand why the first argument contains whitespace, remember that leading unquoted whitespace is never part of an argument, but trailing whitespace always is. It is possible for a macro's definition to change during argument collection, in which case the expansion uses the definition that was in effect at the time the opening `(' was seen. define(`f', `1') => f(define(`f', `2')) =>1 f =>2 It is an error if the end of file occurs while collecting arguments. define( ^D error-->m4:stdin:1: ERROR: end of file in argument list 3.4 On Quoting Arguments to macros ================================== Each argument has leading unquoted whitespace removed. Within each argument, all unquoted parentheses must match. For example, if FOO is a macro, foo(() (`(') `(') is a macro call, with one argument, whose value is `() (() ('. Commas separate arguments, except when they occur inside quotes, comments, or unquoted parentheses, *Note Pseudo Arguments::, for examples. It is common practice to quote all arguments to macros, unless you are sure you want the arguments expanded. Thus, in the above example with the parentheses, the `right' way to do it is like this: foo(`() (() (') It is, however, in certain cases necessary or convenient to leave out quotes for some arguments, and there is nothing wrong in doing it. It just makes life a bit harder, if you are not careful. For consistency, this manual follows the rule of thumb that each layer of parentheses introduces another layer of single quoting, except when showing the consequences of quoting rules. This is done even when the quoted string cannot be a macro, such as with integers when you have not changed the syntax via `changeword' (*note Changeword::). 3.5 Macro expansion =================== When the arguments, if any, to a macro call have been collected, the macro is expanded, and the expansion text is pushed back onto the input (unquoted), and reread. The expansion text from one macro call might therefore result in more macros being called, if the calls are included, completely or partially, in the first macro calls' expansion. Taking a very simple example, if FOO expands to `bar', and BAR expands to `Hello world', the input foo will expand first to `bar', and when this is reread and expanded, into `Hello world'. 4 How to define new macros ************************** Macros can be defined, redefined and deleted in several different ways. Also, it is possible to redefine a macro without losing a previous value, and bring back the original value at a later time. 4.1 Defining a macro ==================== The normal way to define or redefine macros is to use the builtin `define': -- Builtin: define (NAME, [EXPANSION]) Defines NAME to expand to EXPANSION. If EXPANSION is not given, it is taken to be empty. The expansion of `define' is void. The macro `define' is recognized only with parameters. The following example defines the macro FOO to expand to the text `Hello World.'. define(`foo', `Hello world.') => foo =>Hello world. The empty line in the output is there because the newline is not a part of the macro definition, and it is consequently copied to the output. This can be avoided by use of the macro `dnl'. *Note Dnl::, for details. The first argument to `define' should be quoted; otherwise, if the macro is already defined, you will be defining a different macro. This example shows the problems with underquoting, since we did not want to redefine `one': define(foo, one) => define(foo, two) => one =>two GNU `m4' normally replaces only the _topmost_ definition of a macro if it has several definitions from `pushdef' (*note Pushdef::). Some other implementations of `m4' replace all definitions of a macro with `define'. *Note Incompatibilities::, for more details. As a GNU extension, the first argument to `define' does not have to be a simple word. It can be any text string, even the empty string. A macro with a non-standard name cannot be invoked in the normal way, as the name is not recognized. It can only be referenced by the builtins *Note Indir:: and *Note Defn::. Arrays and associative arrays can be simulated by using this trick. define(`array', `defn(format(``array[%d]'', `$1'))') => define(`array_set', `define(format(``array[%d]'', `$1'), `$2')') => array_set(`4', `array element no. 4') => array_set(`17', `array element no. 17') => array(`4') =>array element no. 4 array(eval(`10 + 7')) =>array element no. 17 Change the `%d' to `%s' and it is an associative array. 4.2 Arguments to macros ======================= Macros can have arguments. The Nth argument is denoted by `$n' in the expansion text, and is replaced by the Nth actual argument, when the macro is expanded. Replacement of arguments happens before rescanning, regardless of how many nesting levels of quoting appear in the expansion. Here is an example of a macro with two arguments. It simply exchanges the order of the two arguments. define(`exch', `$2, $1') => exch(`arg1', `arg2') =>arg2, arg1 This can be used, for example, if you like the arguments to `define' to be reversed. define(`exch', `$2, $1') => define(exch(``expansion text'', ``macro'')) => macro =>expansion text *Note Quoting Arguments::, for an explanation of the double quotes. (You should try and improve this example so that clients of `exch' do not have to double quote. *note Answers::) GNU `m4' allows the number following the `$' to consist of one or more digits, allowing macros to have any number of arguments. This is not so in UNIX implementations of `m4', which only recognize one digit. As a special case, the zeroth argument, `$0', is always the name of the macro being expanded. define(`test', ``Macro name: $0'') => test =>Macro name: test If you want quoted text to appear as part of the expansion text, remember that quotes can be nested in quoted strings. Thus, in define(`foo', `This is macro `foo'.') => foo =>This is macro foo. The `foo' in the expansion text is _not_ expanded, since it is a quoted string, and not a name. 4.3 Special arguments to macros =============================== There is a special notation for the number of actual arguments supplied, and for all the actual arguments. The number of actual arguments in a macro call is denoted by `$#' in the expansion text. Thus, a macro to display the number of arguments given can be define(`nargs', `$#') => nargs =>0 nargs() =>1 nargs(`arg1', `arg2', `arg3') =>3 nargs(`commas can be quoted, like this') =>1 nargs(arg1#inside comments, commas do not separate arguments still arg1) =>1 nargs((unquoted parentheses, like this, group arguments)) =>1 The notation `$*' can be used in the expansion text to denote all the actual arguments, unquoted, with commas in between. For example define(`echo', `$*') => echo(arg1, arg2, arg3 , arg4) =>arg1,arg2,arg3 ,arg4 Often each argument should be quoted, and the notation `$@' handles that. It is just like `$*', except that it quotes each argument. A simple example of that is: define(`echo', `$@') => echo(arg1, arg2, arg3 , arg4) =>arg1,arg2,arg3 ,arg4 Where did the quotes go? Of course, they were eaten, when the expanded text were reread by `m4'. To show the difference, try define(`echo1', `$*') => define(`echo2', `$@') => define(`foo', `This is macro `foo'.') => echo1(foo) =>This is macro This is macro foo.. echo1(`foo') =>This is macro foo. echo2(foo) =>This is macro foo. echo2(`foo') =>foo *Note Trace::, if you do not understand this. As another example of the difference, remember that comments encountered in arguments are passed untouched to the macro, and that quoting disables comments. define(`echo1', `$*') => define(`echo2', `$@') => define(`foo', `bar') => echo1(#foo'foo foo) =>#foo'foo =>bar echo2(#foo'foo foo) =>#foobar =>bar' A `$' sign in the expansion text, that is not followed by anything `m4' understands, is simply copied to the macro expansion, as any other text is. define(`foo', `$$$ hello $$$') => foo =>$$$ hello $$$ If you want a macro to expand to something like `$12', the judicious use of nested quoting can put a safe character between the `$' and the next character, relying on the rescanning to remove the nested quote. This will prevent `m4' from interpreting the `$' sign as a reference to an argument. define(`foo', `no nested quote: $1') => foo(`arg') =>no nested quote: arg define(`foo', `nested quote around $: `$'1') => foo(`arg') =>nested quote around $: $1 define(`foo', `nested empty quote after $: $`'1') => foo(`arg') =>nested empty quote after $: $1 define(`foo', `nested quote around next character: $`1'') => foo(`arg') =>nested quote around next character: $1 define(`foo', `nested quote around both: `$1'') => foo(`arg') =>nested quote around both: arg 4.4 Deleting a macro ==================== A macro definition can be removed with `undefine': -- Builtin: undefine (NAME...) For each argument, remove the macro NAME. The macro names must necessarily be quoted, since they will be expanded otherwise. The expansion of `undefine' is void. The macro `undefine' is recognized only with parameters. foo bar blah =>foo bar blah define(`foo', `some')define(`bar', `other')define(`blah', `text') => foo bar blah =>some other text undefine(`foo') => foo bar blah =>foo other text undefine(`bar', `blah') => foo bar blah =>foo bar blah Undefining a macro inside that macro's expansion is safe; the macro still expands to the definition that was in effect at the `('. define(`f', ``$0':$1') => f(f(f(undefine(`f')`hello world'))) =>f:f:f:hello world f(`bye') =>f(bye) It is not an error for NAME to have no macro definition. In that case, `undefine' does nothing. 4.5 Renaming macros =================== It is possible to rename an already defined macro. To do this, you need the builtin `defn': -- Builtin: defn (NAME) Expands to the _quoted definition_ of NAME. If the argument is not a defined macro, the expansion is void. If NAME is a user-defined macro, the quoted definition is simply the quoted expansion text. If, instead, NAME is a builtin, the expansion is a special token, which points to the builtin's internal definition. This token is only meaningful as the second argument to `define' (and `pushdef'), and is silently converted to an empty string in most other contexts. The macro `defn' is recognized only with parameters. Its normal use is best understood through an example, which shows how to rename `undefine' to `zap': define(`zap', defn(`undefine')) => zap(`undefine') => undefine(`zap') =>undefine(zap) In this way, `defn' can be used to copy macro definitions, and also definitions of builtin macros. Even if the original macro is removed, the other name can still be used to access the definition. The fact that macro definitions can be transferred also explains why you should use `$0', rather than retyping a macro's name in its definition: define(`foo', `This is `$0'') => define(`bar', defn(`foo')) => bar =>This is bar Macros used as string variables should be referred through `defn', to avoid unwanted expansion of the text: define(`string', `The macro dnl is very useful ') => string =>The macro defn(`string') =>The macro dnl is very useful => However, it is important to remember that `m4' rescanning is purely textual. If an unbalanced end-quote string occurs in a macro definition, the rescan will see that embedded quote as the termination of the quoted string, and the remainder of the macro's definition will be rescanned unquoted. Thus it is a good idea to avoid unbalanced end-quotes in macro definitions or arguments to macros. define(`foo', a'a) => define(`a', `A') => define(`echo', `$@') => foo =>A'A defn(`foo') =>aA' echo(foo) =>AA' Using `defn' to generate special tokens for builtin macros outside of expected contexts can sometimes trigger warnings. But most of the time, such tokens are silently converted to the empty string. defn(`defn') => define(defn(`divnum'), `cannot redefine a builtin token') error-->m4:stdin:2: Warning: define: invalid macro name ignored => divnum =>0 4.6 Temporarily redefining macros ================================= It is possible to redefine a macro temporarily, reverting to the previous definition at a later time. This is done with the builtins `pushdef' and `popdef': -- Builtin: pushdef (NAME, [EXPANSION]) -- Builtin: popdef (NAME...) Analogous to `define' and `undefine'. These macros work in a stack-like fashion. A macro is temporarily redefined with `pushdef', which replaces an existing definition of NAME, while saving the previous definition, before the new one is installed. If there is no previous definition, `pushdef' behaves exactly like `define'. If a macro has several definitions (of which only one is accessible), the topmost definition can be removed with `popdef'. If there is no previous definition, `popdef' behaves like `undefine'. The expansion of both `pushdef' and `popdef' is void. The macros `pushdef' and `popdef' are recognized only with parameters. define(`foo', `Expansion one.') => foo =>Expansion one. pushdef(`foo', `Expansion two.') => foo =>Expansion two. pushdef(`foo', `Expansion three.') => pushdef(`foo', `Expansion four.') => popdef(`foo') => foo =>Expansion three. popdef(`foo', `foo') => foo =>Expansion one. popdef(`foo') => foo =>foo If a macro with several definitions is redefined with `define', the topmost definition is _replaced_ with the new definition. If it is removed with `undefine', _all_ the definitions are removed, and not only the topmost one. define(`foo', `Expansion one.') => foo =>Expansion one. pushdef(`foo', `Expansion two.') => foo =>Expansion two. define(`foo', `Second expansion two.') => foo =>Second expansion two. undefine(`foo') => foo =>foo Local variables within macros are made with `pushdef' and `popdef'. At the start of the macro a new definition is pushed, within the macro it is manipulated and at the end it is popped, revealing the former definition. It is possible to temporarily redefine a builtin with `pushdef' and `defn'. 4.7 Indirect call of macros =========================== Any macro can be called indirectly with `indir': -- Builtin: indir (NAME, ...) Results in a call to the macro NAME, which is passed the rest of the arguments. If NAME is not defined, an error message is printed, and the expansion is void. The macro `indir' is recognized only with parameters. This can be used to call macros with computed or "invalid" names (`define' allows such names to be defined): define(`$$internal$macro', `Internal macro (name `$0')') => $$internal$macro =>$$internal$macro indir(`$$internal$macro') =>Internal macro (name $$internal$macro) The point is, here, that larger macro packages can have private macros defined, that will not be called by accident. They can _only_ be called through the builtin `indir'. One other point to observe is that argument collection occurs before `indir' invokes NAME, so if argument collection changes the value of NAME, that will be reflected in the final expansion. This is different than the behavior when invoking macros directly, where the definition that was in effect before argument collection is used. define(`f', `1') => f(define(`f', `2')) =>1 indir(`f', define(`f', `3')) =>3 indir(`f', undefine(`f')) error-->m4:stdin:4: undefined macro `f' => 4.8 Indirect call of builtins ============================= Builtin macros can be called indirectly with `builtin': -- Builtin: builtin (NAME, ...) Results in a call to the builtin NAME, which is passed the rest of the arguments. If NAME does not name a builtin, an error message is printed, and the expansion is void. The macro `builtin' is recognized only with parameters. This can be used even if NAME has been given another definition that has covered the original, or been undefined so that no macro maps to the builtin. pushdef(`define', `hidden') => undefine(`undefine') => define(`foo', `bar') =>hidden foo =>foo builtin(`define', `foo', `BAR') => foo =>BAR undefine(`foo') =>undefine(foo) foo =>BAR builtin(`undefine', `foo') => foo =>foo The NAME argument only matches the original name of the builtin, even when the `--prefix-builtins' option (or `-P', *note Invoking m4::) is in effect. This is different from `indir', which only tracks current macro names. Note that `indir' and `builtin' can be used to invoke builtins without arguments, even when they normally require parameters to be recognized; but it will provoke a warning, and result in a void expansion. builtin =>builtin builtin() error-->m4:stdin:2: undefined builtin `' => builtin(`builtin') error-->m4:stdin:3: Warning: too few arguments to builtin `builtin' => builtin(`builtin',) error-->m4:stdin:4: undefined builtin `' => 5 Conditionals, loops, and recursion ************************************ Macros, expanding to plain text, perhaps with arguments, are not quite enough. We would like to have macros expand to different things, based on decisions taken at run-time. For that, we need some kind of conditionals. Also, we would like to have some kind of loop construct, so we could do something a number of times, or while some condition is true. 5.1 Testing if a macro is defined ================================= There are two different builtin conditionals in `m4'. The first is `ifdef': -- Builtin: ifdef (NAME, STRING-1, [STRING-2]) If NAME is defined as a macro, `ifdef' expands to STRING-1, otherwise to STRING-2. If STRING-2 is omitted, it is taken to be the empty string (according to the normal rules). The macro `ifdef' is recognized only with parameters. ifdef(`foo', ``foo' is defined', ``foo' is not defined') =>foo is not defined define(`foo', `') => ifdef(`foo', ``foo' is defined', ``foo' is not defined') =>foo is defined ifdef(`no_such_macro', `yes', `no', `extra argument') error-->m4:stdin:4: Warning: excess arguments to builtin `ifdef' ignored =>no 5.2 If-else construct, or multibranch ===================================== The other conditional, `ifelse', is much more powerful. It can be used as a way to introduce a long comment, as an if-else construct, or as a multibranch, depending on the number of arguments supplied: -- Builtin: ifelse (COMMENT) -- Builtin: ifelse (STRING-1, STRING-2, EQUAL, [NOT-EQUAL]) -- Builtin: ifelse (STRING-1, STRING-2, EQUAL-1, STRING-3, STRING-4, EQUAL-2, ...) Used with only one argument, the `ifelse' simply discards it and produces no output. If called with three or four arguments, `ifelse' expands into EQUAL, if STRING-1 and STRING-2 are equal (character for character), otherwise it expands to NOT-EQUAL. A final fifth argument is ignored, after triggering a warning. If called with six or more arguments, and STRING-1 and STRING-2 are equal, `ifelse' expands into EQUAL-1, otherwise the first three arguments are discarded and the processing starts again. The macro `ifelse' is recognized only with parameters. Using only one argument is a common `m4' idiom for introducing a block comment, as an alternative to repeatedly using `dnl'. This special usage is recognized by GNU `m4', so that in this case, the warning about missing arguments is never triggered. ifelse(`some comments') => ifelse(`foo', `bar') error-->m4:stdin:2: Warning: too few arguments to builtin `ifelse' => Using three or four arguments provides decision points. ifelse(`foo', `bar', `true') => ifelse(`foo', `foo', `true') =>true define(`foo', `bar') => ifelse(foo, `bar', `true', `false') =>true ifelse(foo, `foo', `true', `false') =>false Notice how the first argument was used unquoted; it is common to compare the expansion of a macro with a string. With this macro, you can now reproduce the behavior of many of the builtins, where the macro is recognized only with arguments. define(`foo', `ifelse(`$#', `0', ``$0'', `arguments:$#')') => foo =>foo foo() =>arguments:1 foo(`a', `b', `c') =>arguments:3 However, `ifelse' can take more than four arguments. If given more than four arguments, `ifelse' works like a `case' or `switch' statement in traditional programming languages. If STRING-1 and STRING-2 are equal, `ifelse' expands into EQUAL-1, otherwise the procedure is repeated with the first three arguments discarded. This calls for an example: ifelse(`foo', `bar', `third', `gnu', `gnats') error-->m4:stdin:1: Warning: excess arguments to builtin `ifelse' ignored =>gnu ifelse(`foo', `bar', `third', `gnu', `gnats', `sixth') => ifelse(`foo', `bar', `third', `gnu', `gnats', `sixth', `seventh') =>seventh ifelse(`foo', `bar', `3', `gnu', `gnats', `6', `7', `8') error-->m4:stdin:4: Warning: excess arguments to builtin `ifelse' ignored =>7 Naturally, the normal case will be slightly more advanced than these examples. A common use of `ifelse' is in macros implementing loops of various kinds. 5.3 Loops and recursion ======================= There is no direct support for loops in `m4', but macros can be recursive. There is no limit on the number of recursion levels, other than those enforced by your hardware and operating system. Loops can be programmed using recursion and the conditionals described previously. There is a builtin macro, `shift', which can, among other things, be used for iterating through the actual arguments to a macro: -- Builtin: shift (ARG1, ...) Takes any number of arguments, and expands to all its arguments except ARG1, separated by commas, with each argument quoted. The macro `shift' is recognized only with parameters. shift =>shift shift(`bar') => shift(`foo', `bar', `baz') =>bar,baz An example of the use of `shift' is this macro: -- Composite: reverse (...) Takes any number of arguments, and reverse their order. It is implemented as: define(`reverse', `ifelse(`$#', `0', , `$#', `1', ``$1'', `reverse(shift($@)), `$1'')') => reverse => reverse(`foo') =>foo reverse(`foo', `bar', `gnats', `and gnus') =>and gnus, gnats, bar, foo While not a very interesting macro, it does show how simple loops can be made with `shift', `ifelse' and recursion. It also shows that `shift' is usually used with `$@'. Here is an example of a loop macro that implements a simple for loop. -- Composite: forloop (ITERATOR, START, END, TEXT) Takes the name in ITERATOR, which must be a valid macro name, and successively assign it each integer value from START to END, inclusive. For each assignment to ITERATOR, append TEXT to the expansion of the `forloop'. TEXT may refer to ITERATOR. Any definition of ITERATOR prior to this invocation is restored. It can, for example, be used for simple counting: include(`forloop.m4') => forloop(`i', `1', `8', `i ') =>1 2 3 4 5 6 7 8 For-loops can be nested, like: include(`forloop.m4') => forloop(`i', `1', `4', `forloop(`j', `1', `8', ` (i, j)') ') => (1, 1) (1, 2) (1, 3) (1, 4) (1, 5) (1, 6) (1, 7) (1, 8) => (2, 1) (2, 2) (2, 3) (2, 4) (2, 5) (2, 6) (2, 7) (2, 8) => (3, 1) (3, 2) (3, 3) (3, 4) (3, 5) (3, 6) (3, 7) (3, 8) => (4, 1) (4, 2) (4, 3) (4, 4) (4, 5) (4, 6) (4, 7) (4, 8) => The implementation of the `forloop' macro is fairly straightforward. The `forloop' macro itself is simply a wrapper, which saves the previous definition of the first argument, calls the internal macro `_forloop', and re-establishes the saved definition of the first argument. The macro `_forloop' expands the fourth argument once, and tests to see if it is finished. If it has not finished, it increments the iteration variable (using the predefined macro `incr', *note Incr::), and recurses. Here is the actual implementation of `forloop', distributed as `examples/forloop.m4' in this package: undivert(`forloop.m4') =>divert(`-1') =># forloop(var, from, to, stmt) =>define(`forloop', => `pushdef(`$1', `$2')_forloop(`$1', `$2', `$3', `$4')popdef(`$1')') =>define(`_forloop', => `$4`'ifelse($1, `$3', , => `define(`$1', incr($1))_forloop(`$1', `$2', `$3', `$4')')') =>divert`'dnl => Notice the careful use of quotes. Only three macro arguments are unquoted, each for its own reason. Try to find out _why_ these three arguments are left unquoted, and see what happens if they are quoted. Now, even though these two macros are useful, they are still not robust enough for general use. They lack even basic error handling of cases like start value less than final value, and the first argument not being a name. Correcting these errors are left as an exercise to the reader. 6 How to debug macros and input ******************************* When writing macros for `m4', they often do not work as intended on the first try (as is the case with most programming languages). Fortunately, there is support for macro debugging in `m4'. 6.1 Displaying macro definitions ================================ If you want to see what a name expands into, you can use the builtin `dumpdef': -- Builtin: dumpdef (...) Accepts any number of arguments. If called without any arguments, it displays the definitions of all known names, otherwise it displays the definitions of the names given. The output is printed to the current debug file (usually standard error), and is sorted by name. If an unknown name is encountered, a warning is printed. The expansion of `dumpdef' is void. define(`foo', `Hello world.') => dumpdef(`foo') error-->foo: `Hello world.' => dumpdef(`define') error-->define: => The last example shows how builtin macros definitions are displayed. The definition that is dumped corresponds to what would occur if the macro were to be called at that point, even if other definitions are still live due to redefining a macro during argument collection. pushdef(`f', ``$0'1')pushdef(`f', ``$0'2') => f(popdef(`f')dumpdef(`f')) error-->f: ``$0'1' =>f2 f(popdef(`f')dumpdef(`f')) error-->m4:stdin:3: undefined macro `f' =>f1 *Note Debug Levels::, for information on controlling the details of the display. 6.2 Tracing macro calls ======================= It is possible to trace macro calls and expansions through the builtins `traceon' and `traceoff': -- Builtin: traceon (...) -- Builtin: traceoff (...) When called without any arguments, `traceon' and `traceoff' will turn tracing on and off, respectively, for all defined macros. When called with arguments, only the named macros are affected, whether or not they are currently defined. The expansion of `traceon' and `traceoff' is void. Whenever a traced macro is called and the arguments have been collected, the call is displayed. If the expansion of the macro call is not void, the expansion can be displayed after the call. The output is printed to the current debug file (usually standard error). define(`foo', `Hello World.') => define(`echo', `$@') => traceon(`foo', `echo') => foo error-->m4trace: -1- foo -> `Hello World.' =>Hello World. echo(`gnus', `and gnats') error-->m4trace: -1- echo(`gnus', `and gnats') -> ``gnus',`and gnats'' =>gnus,and gnats The number between dashes is the depth of the expansion. It is one most of the time, signifying an expansion at the outermost level, but it increases when macro arguments contain unquoted macro calls. The maximum number that will appear between dashes is controlled by the option `--nesting-limit' (*note Invoking m4::). Tracing by name is an attribute that is preserved whether the macro is defined or not. This allows the `-t' option to select macros to trace before those macros are defined. traceoff(`foo') => traceon(`foo') => foo =>foo define(`foo', `bar') => foo error-->m4trace: -1- foo -> `bar' =>bar undefine(`foo') => ifdef(`foo', `yes', `no') =>no indir(`foo') error-->m4:stdin:8: undefined macro `foo' => define(`foo', `blah') => foo error-->m4trace: -1- foo -> `blah' =>blah traceoff => foo =>blah Tracing even works on builtins. However, `defn' (*note Defn::) does not transfer tracing status. traceon(`eval', `m4_divnum') => define(`m4_eval', defn(`eval')) => define(`m4_divnum', defn(`divnum')) => eval(divnum) error-->m4trace: -1- eval(`0') -> `0' =>0 m4_eval(m4_divnum) error-->m4trace: -2- m4_divnum -> `0' =>0 *Note Debug Levels::, for information on controlling the details of the display. 6.3 Controlling debugging output ================================ The `-d' option to `m4' (*note Invoking m4::) controls the amount of details presented, when using the macros described in the preceding sections. The FLAGS following the option can be one or more of the following: `a' Show the actual arguments in each macro call. This applies to all macro calls if the `t' flag is used, otherwise only the macros covered by calls of `traceon'. `c' Show several trace lines for each macro call. A line is shown when the macro is seen, but before the arguments are collected; a second line when the arguments have been collected and a third line after the call has completed. `e' Show the expansion of each macro call, if it is not void. This applies to all macro calls if the `t' flag is used, otherwise only the macros covered by calls of `traceon'. `f' Show the name of the current input file in each trace output line. `i' Print a message each time the current input file is changed, giving file name and input line number. `l' Show the current input line number in each trace output line. `p' Print a message when a named file is found through the path search mechanism (*note Search Path::), giving the actual file name used. `q' Quote actual arguments and macro expansions in the display with the current quotes. `t' Trace all macro calls made in this invocation of `m4'. `x' Add a unique `macro call id' to each line of the trace output. This is useful in connection with the `c' flag above. `V' A shorthand for all of the above flags. If no flags are specified with the `-d' option, the default is `aeq'. The examples throughout this manual assume the default flags. There is a builtin macro `debugmode', which allows on-the-fly control of the debugging output format: -- Builtin: debugmode ([FLAGS]) The argument FLAGS should be a subset of the letters listed above. As special cases, if the argument starts with a `+', the flags are added to the current debug flags, and if it starts with a `-', they are removed. If no argument is present, all debugging flags are cleared (as if no `-d' was given), and with an empty argument the flags are reset to the default of `aeq'. The expansion of `debugmode' is void. define(`foo', `FOO') => traceon(`foo') => debugmode() => foo error-->m4trace: -1- foo -> `FOO' =>FOO debugmode => foo error-->m4trace: -1- foo =>FOO debugmode(`+l') => foo error-->m4trace:8: -1- foo =>FOO 6.4 Saving debugging output =========================== Debug and tracing output can be redirected to files using either the `--debugfile' option to `m4' (*note Invoking m4::), or with the builtin macro `debugfile': -- Builtin: debugfile ([FILE]) Sends all further debug and trace output to FILE. If FILE is empty, debug and trace output are discarded. If `debugfile' is called without any arguments, debug and trace output are sent to standard error. This does not affect warnings, error messages, or `errprint' output, which are always sent to standard error. If FILE cannot be opened, the current debug file is unchanged. The expansion of `debugfile' is void. traceon(`divnum') => divnum(`extra') error-->m4:stdin:2: Warning: excess arguments to builtin `divnum' ignored error-->m4trace: -1- divnum(`extra') -> `0' =>0 debugfile() => divnum(`extra') error-->m4:stdin:4: Warning: excess arguments to builtin `divnum' ignored =>0 debugfile => divnum error-->m4trace: -1- divnum -> `0' =>0 7 Input control *************** This chapter describes various builtin macros for controlling the input to `m4'. 7.1 Deleting whitespace in input ================================ The builtin `dnl' stands for "Discard to Next Line": -- Builtin: dnl All characters, up to and including the next newline, are discarded without performing any macro expansion. The expansion of `dnl' is void. It is often used in connection with `define', to remove the newline that follows the call to `define'. Thus define(`foo', `Macro `foo'.')dnl A very simple macro, indeed. foo =>Macro foo. The input up to and including the next newline is discarded, as opposed to the way comments are treated (*note Comments::). Usually, `dnl' is immediately followed by an end of line or some other whitespace. GNU `m4' will produce a warning diagnostic if `dnl' is followed by an open parenthesis. In this case, `dnl' will collect and process all arguments, looking for a matching close parenthesis. All predictable side effects resulting from this collection will take place. `dnl' will return no output. The input following the matching close parenthesis up to and including the next newline, on whatever line containing it, will still be discarded. dnl(`args are ignored, but side effects occur', define(`foo', `like this')) while this text is ignored: undefine(`foo') error-->m4:stdin:2: Warning: excess arguments to builtin `dnl' ignored See how `foo' was defined, foo? =>See how foo was defined, like this? If the end of file is encountered without a newline character, a warning is issued and dnl stops consuming input. define(`hi', `HI') => m4wrap(`m4wrap(`2 hi ')0 hi dnl 1 hi') => ^D error-->m4: Warning: end of file treated as newline =>0 HI 2 HI 7.2 Changing the quote characters ================================= The default quote delimiters can be changed with the builtin `changequote': -- Builtin: changequote ([START = ``'], [END = `'']) This sets START as the new begin-quote delimiter and END as the new end-quote delimiter. If any of the arguments are missing, the default quotes (``' and `'') are used instead of the void arguments. The expansion of `changequote' is void. changequote(`[', `]') => define([foo], [Macro [foo].]) => foo =>Macro foo. The quotation strings can safely contain eight-bit characters. If no single character is appropriate, START and END can be of any length. changequote(`[[[', `]]]') => define([[[foo]]], [[[Macro [[[[[foo]]]]].]]]) => foo =>Macro [[foo]]. Changing the quotes to the empty strings will effectively disable the quoting mechanism, leaving no way to quote text. define(`foo', `Macro `FOO'.') => changequote(, ) => foo =>Macro `FOO'. `foo' =>`Macro `FOO'.' There is no way in `m4' to quote a string containing an unmatched begin-quote, except using `changequote' to change the current quotes. If the quotes should be changed from, say, `[' to `[[', temporary quote characters have to be defined. To achieve this, two calls of `changequote' must be made, one for the temporary quotes and one for the new quotes. Macros are recognized in preference to the begin-quote string, so if a prefix of START can be recognized as a potential macro name, the quoting mechanism is effectively disabled. Unless you use `changeword' (*note Changeword::), this means that START should not begin with a letter or `_' (underscore). define(`hi', `HI') => changequote(`q', `Q') => q hi Q hi =>q HI Q HI changequote => changequote(`-', `EOF') => - hi EOF hi => hi HI Quotes are recognized in preference to argument collection. In particular, if START is a single `(', then argument collection is effectively disabled. For portability with other implementations, it is a good idea to avoid `(', `,', and `)' as the first character in START. define(`echo', `$#:$@:') => define(`hi', `HI') => changequote(`(',`)') => echo(hi) =>0::hi changequote => changequote(`((', `))') => echo(hi) =>1:HI: echo((hi)) =>0::hi changequote => changequote(`,', `)') => echo(hi,hi)bye) =>1:HIhibye: If END is a prefix of START, the end-quote will be recognized in preference to a nested begin-quote. In particular, changing the quotes to have the same string for START and END disables nesting of quotes. When quote nesting is disabled, it is impossible to double-quote strings across macro expansions, so using the same string is not done very often. define(`hi', `HI') => changequote(`""', `"') => ""hi"""hi" =>hihi ""hi" ""hi" =>hi hi ""hi"" "hi" =>hi" "HI" changequote => `hi`hi'hi' =>hi`hi'hi changequote(`"', `"') => "hi"hi"hi" =>hiHIhi It is an error if the end of file occurs within a quoted string. `dangling quote ^D error-->m4:stdin:1: ERROR: end of file in string 7.3 Changing the comment delimiters =================================== The default comment delimiters can be changed with the builtin macro `changecom': -- Builtin: changecom ([START], [END]) This sets START as the new begin-comment delimiter and END as the new end-comment delimiter. If only one argument is provided, newline becomes the new end-comment delimiter. The comment delimiters can be of any length. Omitting the first argument, or using the empty string as the first argument, disables comments. The expansion of `changecom' is void. define(`comment', `COMMENT') => # A normal comment =># A normal comment changecom(`/*', `*/') => # Not a comment anymore =># Not a COMMENT anymore But: /* this is a comment now */ while this is not a comment =>But: /* this is a comment now */ while this is not a COMMENT Note how comments are copied to the output, much as if they were quoted strings. If you want the text inside a comment expanded, quote the begin-comment delimiter. Calling `changecom' without any arguments, or with an empty string for the first argument, disables the commenting mechanism completely. To restore the original comment start of `#', you must explicitly ask for it. define(`comment', `COMMENT') => changecom => # Not a comment anymore =># Not a COMMENT anymore changecom(`#') => # comment again =># comment again The comment strings can safely contain eight-bit characters. Comments are recognized in preference to macros. However, this is not compatible with other implementations, where macros and even quoting takes precedence over comments, so it may change in a future release. For portability, this means that START should not begin with a letter or `_' (underscore), and that neither the start-quote nor the start-comment string should be a prefix of the other. define(`hi', `HI') => changecom(`q', `Q') => q hi Q hi =>q hi Q HI Comments are recognized in preference to argument collection. In particular, if START is a single `(', then argument collection is effectively disabled. For portability with other implementations, it is a good idea to avoid `(', `,', and `)' as the first character in START. define(`echo', `$#:$@:') => define(`hi', `HI') => changecom(`(',`)') => echo(hi) =>0::(hi) changecom => changecom(`((', `))') => echo(hi) =>1:HI: echo((hi)) =>0::((hi)) changecom(`,', `)') => echo(hi,hi)bye) =>1:HI,hi)bye: It is an error if the end of file occurs within a comment. changecom(`/*', `*/') => /*dangling comment ^D error-->m4:stdin:1: ERROR: end of file in comment 7.4 Changing the lexical structure of words =========================================== The macro `changeword' and all associated functionality is experimental. It is only available if the `--enable-changeword' option was given to `configure', at GNU `m4' installation time. The functionality will go away in the future, to be replaced by other new features that are more efficient at providing the same capabilities. _Do not rely on it_. Please direct your comments about it the same way you would do for bugs. A file being processed by `m4' is split into quoted strings, words (potential macro names) and simple tokens (any other single character). Initially a word is defined by the following regular expression: [_a-zA-Z][_a-zA-Z0-9]* Using `changeword', you can change this regular expression: -- Optional builtin: changeword (REGEX) Changes the regular expression for recognizing macro names to be REGEX. If REGEX is empty, use `[_a-zA-Z][_a-zA-Z0-9]*'. REGEX must obey the constraint that every prefix of the desired final pattern is also accepted by the regular expression. If REGEX contains grouping parentheses, the macro invoked is the portion that matched the first group, rather than the entire matching string. The expansion of `changeword' is void. The macro `changeword' is recognized only with parameters. Relaxing the lexical rules of `m4' might be useful (for example) if you wanted to apply translations to a file of numbers: ifdef(`changeword', `', `errprint(` skipping: no changeword support ')m4exit(`77')')dnl changeword(`[_a-zA-Z0-9]+') => define(`1', `0')1 =>0 Tightening the lexical rules is less useful, because it will generally make some of the builtins unavailable. You could use it to prevent accidental call of builtins, for example: ifdef(`changeword', `', `errprint(` skipping: no changeword support ')m4exit(`77')')dnl define(`_indir', defn(`indir')) => changeword(`_[_a-zA-Z0-9]*') => esyscmd(`foo') =>esyscmd(foo) _indir(`esyscmd', `echo hi') =>hi => Because `m4' constructs its words a character at a time, there is a restriction on the regular expressions that may be passed to `changeword'. This is that if your regular expression accepts `foo', it must also accept `f' and `fo'. ifdef(`changeword', `', `errprint(` skipping: no changeword support ')m4exit(`77')')dnl define(`foo ', `bar ') => dnl This example wants to recognize changeword, dnl, and `foo\n'. dnl First, we check that our regexp will match. regexp(`changeword', `[cd][a-z]*\|foo[ ]') =>0 regexp(`foo ', `[cd][a-z]*\|foo[ ]') =>0 regexp(`f', `[cd][a-z]*\|foo[ ]') =>-1 foo =>foo changeword(`[cd][a-z]*\|foo[ ]') => dnl Even though `foo\n' matches, we forgot to allow `f'. foo =>foo changeword(`[cd][a-z]*\|fo*[ ]?') => dnl Now we can call `foo\n'. foo =>bar `changeword' has another function. If the regular expression supplied contains any grouped subexpressions, then text outside the first of these is discarded before symbol lookup. So: ifdef(`changeword', `', `errprint(` skipping: no changeword support ')m4exit(`77')')dnl ifdef(`__unix__', , `errprint(` skipping: syscmd does not have unix semantics ')m4exit(`77')')dnl changecom(`/*', `*/')dnl define(`foo', `bar')dnl changeword(`#\([_a-zA-Z0-9]*\)') => #esyscmd(`echo foo \#foo') =>foo bar => `m4' now requires a `#' mark at the beginning of every macro invocation, so one can use `m4' to preprocess plain text without losing various words like `divert'. In `m4', macro substitution is based on text, while in TeX, it is based on tokens. `changeword' can throw this difference into relief. For example, here is the same idea represented in TeX and `m4'. First, the TeX version: \def\a{\message{Hello}} \catcode`\@=0 \catcode`\\=12 @a @bye =>Hello Then, the `m4' version: ifdef(`changeword', `', `errprint(` skipping: no changeword support ')m4exit(`77')')dnl define(`a', `errprint(`Hello')')dnl changeword(`@\([_a-zA-Z0-9]*\)') => @a =>errprint(Hello) In the TeX example, the first line defines a macro `a' to print the message `Hello'. The second line defines <@> to be usable instead of <\> as an escape character. The third line defines <\> to be a normal printing character, not an escape. The fourth line invokes the macro `a'. So, when TeX is run on this file, it displays the message `Hello'. When the `m4' example is passed through `m4', it outputs `errprint(Hello)'. The reason for this is that TeX does lexical analysis of macro definition when the macro is _defined_. `m4' just stores the text, postponing the lexical analysis until the macro is _used_. You should note that using `changeword' will slow `m4' down by a factor of about seven, once it is changed to something other than the default regular expression. You can invoke `changeword' with the empty string to restore the default word definition, and regain the parsing speed. 7.5 Saving text until end of input ================================== It is possible to `save' some text until the end of the normal input has been seen. Text can be saved, to be read again by `m4' when the normal input has been exhausted. This feature is normally used to initiate cleanup actions before normal exit, e.g., deleting temporary files. To save input text, use the builtin `m4wrap': -- Builtin: m4wrap (STRING, ...) Stores STRING in a safe place, to be reread when end of input is reached. As a GNU extension, additional arguments are concatenated with a space to the STRING. The expansion of `m4wrap' is void. The macro `m4wrap' is recognized only with parameters. define(`cleanup', `This is the `cleanup' action. ') => m4wrap(`cleanup') => This is the first and last normal input line. =>This is the first and last normal input line. ^D =>This is the cleanup action. The saved input is only reread when the end of normal input is seen, and not if `m4exit' is used to exit `m4'. It is safe to call `m4wrap' from saved text, but then the order in which the saved text is reread is undefined. If `m4wrap' is not used recursively, the saved pieces of text are reread in the opposite order in which they were saved (LIFO--last in, first out). However, this behavior is likely to change in a future release, to match POSIX, so you should not depend on this order. Here is an example of implementing a factorial function using `m4wrap': define(`f', `ifelse(`$1', `0', `Answer: 0!=1 ', eval(`$1>1'), `0', `Answer: $2$1=eval(`$2$1') ', `m4wrap(`f(decr(`$1'), `$2$1*')')')') => f(`10') => ^D =>Answer: 10*9*8*7*6*5*4*3*2*1=3628800 Invocations of `m4wrap' at the same recursion level are concatenated and rescanned as usual: define(`aa', `AA ') => m4wrap(`a')m4wrap(`a') => ^D =>AA however, the transition between recursion levels behaves like an end of file condition between two input files. m4wrap(`m4wrap(`)')len(abc') => ^D error-->m4: ERROR: end of file in argument list 8 File inclusion **************** `m4' allows you to include named files at any point in the input. 8.1 Including named files ========================= There are two builtin macros in `m4' for including files: -- Builtin: include (FILE) -- Builtin: sinclude (FILE) Both macros cause the file named FILE to be read by `m4'. When the end of the file is reached, input is resumed from the previous input file. The expansion of `include' and `sinclude' is therefore the contents of FILE. If FILE does not exist (or cannot be read), the expansion is void, and `include' will fail with an error while `sinclude' is silent. The empty string counts as a file that does not exist. The macros `include' and `sinclude' are recognized only with parameters. include(`none') => error-->m4:stdin:1: cannot open `none': No such file or directory include() => error-->m4:stdin:2: cannot open `': No such file or directory sinclude(`none') => sinclude() => The rest of this section assumes that `m4' is invoked with the `-I' option (*note Invoking m4::) pointing to the `examples' directory shipped as part of the GNU `m4' package. The file `examples/incl.m4' in the distribution contains the lines: Include file start foo Include file end Normally file inclusion is used to insert the contents of a file into the input stream. The contents of the file will be read by `m4' and macro calls in the file will be expanded: define(`foo', `FOO') => include(`incl.m4') =>Include file start =>FOO =>Include file end => The fact that `include' and `sinclude' expand to the contents of the file can be used to define macros that operate on entire files. Here is an example, which defines `bar' to expand to the contents of `incl.m4': define(`bar', include(`incl.m4')) => This is `bar': >>bar<< =>This is bar: >>Include file start =>foo =>Include file end =><< This use of `include' is not trivial, though, as files can contain quotes, commas, and parentheses, which can interfere with the way the `m4' parser works. GNU `m4' seamlessly concatenates the file contents with the next character, even if the included file ended in the middle of a comment, string, or macro call. These conditions are only treated as end of file errors if specified as input files on the command line. 8.2 Searching for include files =============================== GNU `m4' allows included files to be found in other directories than the current working directory. If a file is not found in the current working directory, and the file name is not absolute, the file will be looked for in a specified search path. First, the directories specified with the `-I' option will be searched, in the order found on the command line (*note Invoking m4::). Second, if the `M4PATH' environment variable is set, it is expected to contain a colon-separated list of directories, which will be searched in order. If the automatic search for include-files causes trouble, the `p' debug flag (*note Debug Levels::) can help isolate the problem. 9 Diverting and undiverting output ********************************** Diversions are a way of temporarily saving output. The output of `m4' can at any time be diverted to a temporary file, and be reinserted into the output stream, "undiverted", again at a later time. Numbered diversions are counted from 0 upwards, diversion number 0 being the normal output stream. The number of simultaneous diversions is limited mainly by the memory used to describe them, because GNU `m4' tries to keep diversions in memory. However, there is a limit to the overall memory usable by all diversions taken altogether (512K, currently). When this maximum is about to be exceeded, a temporary file is opened to receive the contents of the biggest diversion still in memory, freeing this memory for other diversions. So, it is theoretically possible that the number of diversions be limited by the number of available file descriptors. 9.1 Diverting output ==================== Output is diverted using `divert': -- Builtin: divert ([NUMBER = `0']) The current diversion is changed to NUMBER. If NUMBER is left out or empty, it is assumed to be zero. If NUMBER cannot be parsed, the diversion is unchanged. The expansion of `divert' is void. When all the `m4' input will have been processed, all existing diversions are automatically undiverted, in numerical order. divert(`1') This text is diverted. divert => This text is not diverted. =>This text is not diverted. ^D => =>This text is diverted. Several calls of `divert' with the same argument do not overwrite the previous diverted text, but append to it. Diversions are printed after any wrapped text is expanded. define(`text', `TEXT') => divert(`1')`diverted text.' divert => m4wrap(`Wrapped text preceeds ') => ^D =>Wrapped TEXT preceeds diverted text. If output is diverted to a non-existent diversion, it is simply discarded. This can be used to suppress unwanted output. A common example of unwanted output is the trailing newlines after macro definitions. Here is how to avoid them. divert(`-1') define(`foo', `Macro `foo'.') define(`bar', `Macro `bar'.') divert => This is a common programming idiom in `m4'. Note that `divert' is an English word, but also an active macro without arguments. When processing plain text, the word might appear in normal text and be unintentionally swallowed as a macro invocation. One way to avoid this is to use the `-P' option to rename all builtins (*note Invoking m4::). Another is to write a wrapper that requires a parameter to be recognized. We decided to divert the stream for irrigation. =>We decided to the stream for irrigation. define(`divert', `ifelse(`$#', `0', ``$0'', `builtin(`$0', $@)')') => divert(-1) Ignored text. divert(0) => We decided to divert the stream for irrigation. =>We decided to divert the stream for irrigation. 9.2 Undiverting output ====================== Diverted text can be undiverted explicitly using the builtin `undivert': -- Builtin: undivert ([NUMBER]...) Undiverts the diversions given by the arguments, in the order given. If no arguments are supplied, all diversions are undiverted, in numerical order. As a GNU extension, if NUMBER is not numeric, treat it as a file name instead. The expansion of `undivert' is void. divert(`1') This text is diverted. divert => This text is not diverted. =>This text is not diverted. undivert(`1') => =>This text is diverted. => Notice the last two blank lines. One of them comes from the newline following `undivert', the other from the newline that followed the `divert'! A diversion often starts with a blank line like this. When diverted text is undiverted, it is _not_ reread by `m4', but rather copied directly to the current output, and it is therefore not an error to undivert into a diversion. Undiverting the empty string is the same as specifying diversion 0; in either case nothing happens since the output has already been flushed. divert(`1')diverted text divert => undivert() => undivert(`0') => undivert =>diverted text => When a diversion has been undiverted, the diverted text is discarded, and it is not possible to bring back diverted text more than once. divert(`1') This text is diverted first. divert(`0')undivert(`1')dnl => =>This text is diverted first. undivert(`1') => divert(`1') This text is also diverted but not appended. divert(`0')undivert(`1')dnl => =>This text is also diverted but not appended. Attempts to undivert the current diversion are silently ignored. Thus, when the current diversion is not 0, the current diversion does not get rearranged among the other diversions. divert(`1')one divert(`2')two divert(`3')three divert(`2')undivert`'dnl divert`'undivert`'dnl =>two =>one =>three GNU `m4' allows named files to be undiverted. Given a non-numeric argument, the contents of the file named will be copied, uninterpreted, to the current output. This complements the builtin `include' (*note Include::). To illustrate the difference, the file `examples/foo' contains the word `bar': define(`bar', `BAR') => undivert(`foo') =>bar => include(`foo') =>BAR => If the file is not found (or cannot be read), an error message is issued, and the expansion is void. 9.3 Diversion numbers ===================== The current diversion is tracked by the builtin `divnum': -- Builtin: divnum Expands to the number of the current diversion. Initial divnum =>Initial 0 divert(`1') Diversion one: divnum divert(`2') Diversion two: divnum ^D => =>Diversion one: 1 => =>Diversion two: 2 9.4 Discarding diverted text ============================ Often it is not known, when output is diverted, whether the diverted text is actually needed. Since all non-empty diversion are brought back on the main output stream when the end of input is seen, a method of discarding a diversion is needed. If all diversions should be discarded, the easiest is to end the input to `m4' with `divert(`-1')' followed by an explicit `undivert': divert(`1') Diversion one: divnum divert(`2') Diversion two: divnum divert(`-1') undivert ^D No output is produced at all. Clearing selected diversions can be done with the following macro: -- Composite: cleardivert ([DIVERSION]...) Discard the contents of each listed diversion. define(`cleardivert', `pushdef(`_n', divnum)divert(`-1')undivert($@)divert(_n)popdef(`_n')') => It is called just like `undivert', but the effect is to clear the diversions, given by the arguments. (This macro has a nasty bug! You should try to see if you can find it and correct it. *note Answers::) 10 Macros for text handling *************************** There are a number of builtins in `m4' for manipulating text in various ways, extracting substrings, searching, substituting, and so on. 10.1 Calculating length of strings ================================== The length of a string can be calculated by `len': -- Builtin: len (STRING) Expands to the length of STRING, as a decimal number. The macro `len' is recognized only with parameters. len() =>0 len(`abcdef') =>6 10.2 Searching for substrings ============================= Searching for substrings is done with `index': -- Builtin: index (STRING, SUBSTRING) Expands to the index of the first occurrence of SUBSTRING in STRING. The first character in STRING has index 0. If SUBSTRING does not occur in STRING, `index' expands to `-1'. The macro `index' is recognized only with parameters. index(`gnus, gnats, and armadillos', `nat') =>7 index(`gnus, gnats, and armadillos', `dag') =>-1 Omitting SUBSTRING evokes a warning, but still produces output. index(`abc') error-->m4:stdin:1: Warning: too few arguments to builtin `index' =>0 10.3 Searching for regular expressions ====================================== Searching for regular expressions is done with the builtin `regexp': -- Builtin: regexp (STRING, REGEXP, [REPLACEMENT]) Searches for REGEXP in STRING. The syntax for regular expressions is the same as in GNU Emacs. *Note Syntax of Regular Expressions: (emacs)Regexps. If REPLACEMENT is omitted, `regexp' expands to the index of the first match of REGEXP in STRING. If REGEXP does not match anywhere in STRING, it expands to -1. If REPLACEMENT is supplied, and there was a match, `regexp' changes the expansion to this argument, with `\N' substituted by the text matched by the Nth parenthesized sub-expression of REGEXP, up to nine sub-expressions. The escape `\&' is replaced by the text of the entire regular expression matched. For all other characters, `\' treats the next character literally. A warning is issued if there were fewer sub-expressions than the `\N' requested, or if there is a trailing `\'. If there was no match, `regexp' expands to the empty string. The macro `regexp' is recognized only with parameters. regexp(`GNUs not Unix', `\<[a-z]\w+') =>5 regexp(`GNUs not Unix', `\-1 regexp(`GNUs not Unix', `\w\(\w+\)$', `*** \& *** \1 ***') =>*** Unix *** nix *** regexp(`GNUs not Unix', `\ Here are some more examples on the handling of backslash: regexp(`abc', `\(b\)', `\\\10\a') =>\b0a regexp(`abc', `b', `\1\') error-->m4:stdin:2: Warning: sub-expression 1 not present error-->m4:stdin:2: Warning: trailing \ ignored in replacement => regexp(`abc', `\(\(d\)?\)\(c\)', `\1\2\3\4\5\6') error-->m4:stdin:3: Warning: sub-expression 4 not present error-->m4:stdin:3: Warning: sub-expression 5 not present error-->m4:stdin:3: Warning: sub-expression 6 not present =>c Omitting REGEXP evokes a warning, but still produces output. regexp(`abc') error-->m4:stdin:1: Warning: too few arguments to builtin `regexp' =>0 10.4 Extracting substrings ========================== Substrings are extracted with `substr': -- Builtin: substr (STRING, FROM, [LENGTH]) Expands to the substring of STRING, which starts at index FROM, and extends for LENGTH characters, or to the end of STRING, if LENGTH is omitted. The starting index of a string is always 0. The expansion is empty if there is an error parsing FROM or LENGTH, if FROM is beyond the end of STRING, or if LENGTH is negative. The macro `substr' is recognized only with parameters. substr(`gnus, gnats, and armadillos', `6') =>gnats, and armadillos substr(`gnus, gnats, and armadillos', `6', `5') =>gnats Omitting FROM evokes a warning, but still produces output. substr(`abc') error-->m4:stdin:1: Warning: too few arguments to builtin `substr' =>abc substr(`abc',) error-->m4:stdin:2: empty string treated as 0 in builtin `substr' =>abc 10.5 Translating characters =========================== Character translation is done with `translit': -- Builtin: translit (STRING, CHARS, [REPLACEMENT]) Expands to STRING, with each character that occurs in CHARS translated into the character from REPLACEMENT with the same index. If REPLACEMENT is shorter than CHARS, the excess characters are deleted from the expansion. If REPLACEMENT is omitted, all characters in STRING that are present in CHARS are deleted from the expansion. As a GNU extension, both CHARS and REPLACEMENT can contain character-ranges, e.g., `a-z' (meaning all lowercase letters) or `0-9' (meaning all digits). To include a dash `-' in CHARS or REPLACEMENT, place it first or last. It is not an error for the last character in the range to be `larger' than the first. In that case, the range runs backwards, i.e., `9-0' means the string `9876543210'. The macro `translit' is recognized only with parameters. translit(`GNUs not Unix', `A-Z') =>s not nix translit(`GNUs not Unix', `a-z', `A-Z') =>GNUS NOT UNIX translit(`GNUs not Unix', `A-Z', `z-a') =>tmfs not fnix The first example deletes all uppercase letters, the second converts lowercase to uppercase, and the third `mirrors' all uppercase letters, while converting them to lowercase. The two first cases are by far the most common. Omitting CHARS evokes a warning, but still produces output. translit(`abc') error-->m4:stdin:1: Warning: too few arguments to builtin `translit' =>abc 10.6 Substituting text by regular expression ============================================ Global substitution in a string is done by `patsubst': -- Builtin: patsubst (STRING, REGEXP, [REPLACEMENT]) Searches STRING for matches of REGEXP, and substitutes REPLACEMENT for each match. The syntax for regular expressions is the same as in GNU Emacs (*note Regexp::). The parts of STRING that are not covered by any match of REGEXP are copied to the expansion. Whenever a match is found, the search proceeds from the end of the match, so a character from STRING will never be substituted twice. If REGEXP matches a string of zero length, the start position for the search is incremented, to avoid infinite loops. When a replacement is to be made, REPLACEMENT is inserted into the expansion, with `\N' substituted by the text matched by the Nth parenthesized sub-expression of PATSUBST, for up to nine sub-expressions. The escape `\&' is replaced by the text of the entire regular expression matched. For all other characters, `\' treats the next character literally. A warning is issued if there were fewer sub-expressions than the `\N' requested, or if there is a trailing `\'. The REPLACEMENT argument can be omitted, in which case the text matched by REGEXP is deleted. The macro `patsubst' is recognized only with parameters. patsubst(`GNUs not Unix', `^', `OBS: ') =>OBS: GNUs not Unix patsubst(`GNUs not Unix', `\<', `OBS: ') =>OBS: GNUs OBS: not OBS: Unix patsubst(`GNUs not Unix', `\w*', `(\&)') =>(GNUs)() (not)() (Unix)() patsubst(`GNUs not Unix', `\w+', `(\&)') =>(GNUs) (not) (Unix) patsubst(`GNUs not Unix', `[A-Z][a-z]+') =>GN not patsubst(`GNUs not Unix', `not', `NOT\') error-->m4:stdin:6: Warning: trailing \ ignored in replacement =>GNUs NOT Unix Here is a slightly more realistic example, which capitalizes individual word or whole sentences, by substituting calls of the macros `upcase' and `downcase' into the strings. -- Composite: upcase (TEXT) -- Composite: downcase (TEXT) -- Composite: capitalize (TEXT) Expand to TEXT, but with capitalization changed: `upcase' changes all letters to upper case, `downcase' changes all letters to lower case, and `capitalize' changes the first character of each word to upper case and the remaining characters to lower case. define(`upcase', `translit(`$*', `a-z', `A-Z')')dnl define(`downcase', `translit(`$*', `A-Z', `a-z')')dnl define(`capitalize1', `regexp(`$1', `^\(\w\)\(\w*\)', `upcase(`\1')`'downcase(`\2')')')dnl define(`capitalize', `patsubst(`$1', `\w+', `capitalize1(`\&')')')dnl capitalize(`GNUs not Unix') =>Gnus Not Unix While `regexp' replaces the whole input with the replacement as soon as there is a match, `patsubst' replaces each _occurrence_ of a match and preserves non-matching pieces: define(`patreg', `patsubst($@) regexp($@)')dnl patreg(`bar foo baz Foo', `foo\|Foo', `FOO') =>bar FOO baz FOO =>FOO patreg(`aba abb 121', `\(.\)\(.\)\1', `\2\1\2') =>bab abb 212 =>bab Omitting REGEXP evokes a warning, but still produces output. patsubst(`abc') error-->m4:stdin:1: Warning: too few arguments to builtin `patsubst' =>abc 10.7 Formatted output ===================== Formatted output can be made with `format': -- Builtin: format (FORMAT-STRING, ...) Works much like the C function `printf'. The first argument FORMAT-STRING can contain `%' specifications which are satisfied by additional arguments, and the expansion of `format' is the formatted string. The macro `format' is recognized only with parameters. Its use is best described by a few examples: define(`foo', `The brown fox jumped over the lazy dog') => format(`The string "%s" uses %d characters', foo, len(foo)) =>The string "The brown fox jumped over the lazy dog" uses 38 characters format(`%.0f', `56789.9876') =>56790 len(format(`%-*X', `300', `1')) =>300 Using the `forloop' macro defined in *Note Loops::, this example shows how `format' can be used to produce tabular output. include(`forloop.m4') => forloop(`i', `1', `10', `format(`%6d squared is %10d ', i, eval(i**2))') => 1 squared is 1 => 2 squared is 4 => 3 squared is 9 => 4 squared is 16 => 5 squared is 25 => 6 squared is 36 => 7 squared is 49 => 8 squared is 64 => 9 squared is 81 => 10 squared is 100 => The builtin `format' is modeled after the ANSI C `printf' function, and supports these `%' specifiers: `c', `s', `d', `o', `x', `X', `u', `e', `E', `f', `F', `g', `G', and `%'; it supports field widths and precisions, and the modifiers `+', `-', ` ', `0', `#', `h' and `l'. For more details on the functioning of `printf', see the C Library Manual. For now, unrecognized specifiers are silently ignored, but it is anticipated that a future release of GNU `m4' will support more specifiers, and give warnings when problems are encountered. Likewise, escape sequences are not yet recognized. 11 Macros for doing arithmetic ****************************** Integer arithmetic is included in `m4', with a C-like syntax. As convenient shorthands, there are builtins for simple increment and decrement operations. 11.1 Decrement and increment operators ====================================== Increment and decrement of integers are supported using the builtins `incr' and `decr': -- Builtin: incr (NUMBER) -- Builtin: decr (NUMBER) Expand to the numerical value of NUMBER, incremented or decremented, respectively, by one. Except for the empty string, the expansion is empty if NUMBER could not be parsed. The macros `incr' and `decr' are recognized only with parameters. incr(`4') =>5 decr(`7') =>6 incr() error-->m4:stdin:3: empty string treated as 0 in builtin `incr' =>1 decr() error-->m4:stdin:4: empty string treated as 0 in builtin `decr' =>-1 11.2 Evaluating integer expressions =================================== Integer expressions are evaluated with `eval': -- Builtin: eval (EXPRESSION, [RADIX = `10'], [WIDTH]) Expands to the value of EXPRESSION. The expansion is empty if an error is encountered while parsing the arguments. If specified, RADIX and WIDTH control the format of the output. The macro `eval' is recognized only with parameters. Expressions can contain the following operators, listed in order of decreasing precedence. `+ -' Unary plus and minus `**' Exponentiation `* / %' Multiplication, division and modulo `+ -' Addition and subtraction `<< >>' Shift left or right `== != > >= < <=' Relational operators `!' Logical negation `~' Bitwise negation `&' Bitwise and `^' Bitwise exclusive-or `|' Bitwise or `&&' Logical and `||' Logical or All operators, except exponentiation, are left associative. Note that some older `m4' implementations use `^' as an alternate operator for exponentiation, although POSIX requires the C behavior of bitwise exclusive-or. On the other hand, the precedence of `~' and `!' are different in GNU `m4' than they are in C, matching the precedence in traditional `m4' implementations. This behavior is likely to change in a future version to match POSIX, so use parentheses to force the desired precedence. Within EXPRESSION, (but not RADIX or WIDTH), numbers without a special prefix are decimal. A simple `0' prefix introduces an octal number. `0x' introduces a hexadecimal number. `0b' introduces a binary number. `0r' introduces a number expressed in any radix between 1 and 36: the prefix should be immediately followed by the decimal expression of the radix, a colon, then the digits making the number. For radix 1, leading zeros are ignored and all remaining digits must be `1'; for all other radices, the digits are `0', `1', `2', .... Beyond `9', the digits are `a', `b' ... up to `z'. Lower and upper case letters can be used interchangeably in numbers prefixes and as number digits. Parentheses may be used to group subexpressions whenever needed. For the relational operators, a true relation returns `1', and a false relation return `0'. Here are a few examples of use of `eval'. eval(`-3 * 5') =>-15 eval(index(`Hello world', `llo') >= 0) =>1 eval(`0r1:0111 + 0b100 + 0r3:12') =>12 define(`square', `eval(`('$1`)**2')') => square(`9') =>81 square(square(`5')`+1') =>676 define(`foo', `666') => eval(`foo/6') error-->m4:stdin:8: bad expression in eval: foo/6 => eval(foo/6) =>111 As the last two lines show, `eval' does not handle macro names, even if they expand to a valid expression (or part of a valid expression). Therefore all macros must be expanded before they are passed to `eval'. All evaluation is done with 32-bit signed integers, assuming 2's-complement with wrap-around. The shift operators are defined in GNU `m4' by doing an implicit bit-wise and of the right-hand operand with 0x1f, and sign-extension with right shift. eval(0x80000000 / -1) =>-2147483648 eval(0x80000000 % -1) =>0 eval(0x7fffffff) =>2147483647 incr(eval(0x7fffffff)) =>-2147483648 eval(-4 >> 33) =>-2 If RADIX is specified, it specifies the radix to be used in the expansion. The default radix is 10; this is also the case if RADIX is the empty string. It is an error if the radix is outside the range of 1 through 36, inclusive. The result of `eval' is always taken to be signed. No radix prefix is output, and for radices greater than 10, the digits are lower case. The WIDTH argument specifies the minimum output width, excluding any negative sign. The result is zero-padded to extend the expansion to the requested width. It is an error if the width is negative. On error, the expansion of `eval' is empty. eval(`666', `10') =>666 eval(`666', `11') =>556 eval(`666', `6') =>3030 eval(`666', `6', `10') =>0000003030 eval(`-666', `6', `10') =>-0000003030 eval(`10', `', `0') =>10 `0r1:'eval(`10', `1', `11') =>0r1:01111111111 eval(`10', `16') =>a 12 Macros for running shell commands ************************************ There are a few builtin macros in `m4' that allow you to run shell commands from within `m4'. Note that the definition of a valid shell command is system dependent. On UNIX systems, this is the typical `/bin/sh'. But on other systems, such as native Windows, the shell has a different syntax of commands that it understands. Some examples in this chapter assume `/bin/sh', and also demonstrate how to quit early with a known exit value if this is not the case. 12.1 Determining the platform ============================= Sometimes it is desirable for an input file to know which platform `m4' is running on. GNU `m4' provides several macros that are predefined to expand to the empty string; checking for their existence will confirm platform details. -- Optional builtin: __gnu__ -- Optional builtin: __os2__ -- Optional builtin: os2 -- Optional builtin: __unix__ -- Optional builtin: unix -- Optional builtin: __windows__ -- Optional builtin: windows Each of these macros is conditionally defined as needed to describe the environment of `m4'. If defined, each macro expands to the empty string. When GNU extensions are in effect (that is, when you did not use the `-G' option, *note Invoking m4::), GNU `m4' will define the macro `__gnu__' to expand to the empty string. __gnu__ => ifdef(`__gnu__', `Extensions are active') =>Extensions are active On UNIX systems, GNU `m4' will define `__unix__' by default, or `unix' when the `-G' option is specified. On native Windows systems, GNU `m4' will define `__windows__' by default, or `windows' when the `-G' option is specified. On OS/2 systems, GNU `m4' will define `__os2__' by default, or `os2' when the `-G' option is specified. If GNU `m4' does not provide a platform macro for your system, please report that as a bug. define(`provided', `0') => ifdef(`__unix__', `define(`provided', incr(provided))') => ifdef(`__windows__', `define(`provided', incr(provided))') => ifdef(`__os2__', `define(`provided', incr(provided))') => provided =>1 12.2 Executing simple commands ============================== Any shell command can be executed, using `syscmd': -- Builtin: syscmd (SHELL-COMMAND) Executes SHELL-COMMAND as a shell command. The expansion of `syscmd' is void, _not_ the output from SHELL-COMMAND! Output or error messages from SHELL-COMMAND are not read by `m4'. *Note Esyscmd::, if you need to process the command output. Prior to executing the command, `m4' flushes its buffers. The default standard input, output and error of SHELL-COMMAND are the same as those of `m4'. The macro `syscmd' is recognized only with parameters. define(`foo', `FOO') => syscmd(`echo foo') =>foo => Note how the expansion of `syscmd' keeps the trailing newline of the command, as well as using the newline that appeared after the macro. As an example of SHELL-COMMAND using the same standard input as `m4', the command line `echo "m4wrap(\`syscmd(\`cat')')" | m4' will tell `m4' to read all of its input before executing the wrapped text, then hand a valid (albeit emptied) pipe as standard input for the `cat' subcommand. Therefore, you should be careful when using standard input (either by specifying no files, or by passing `-' as a file name on the command line, *note Invoking m4::), and also invoking subcommands via `syscmd' or `esyscmd' that consume data from standard input. When standard input is a seekable file, the subprocess will pick up with the next character not yet processed by `m4'; when it is a pipe or other non-seekable file, there is no guarantee how much data will already be buffered by `m4' and thus unavailable to the child. 12.3 Reading the output of commands =================================== If you want `m4' to read the output of a shell command, use `esyscmd': -- Builtin: esyscmd (SHELL-COMMAND) Expands to the standard output of the shell command SHELL-COMMAND. Prior to executing the command, `m4' flushes its buffers. The default standard input and error output of SHELL-COMMAND are the same as those of `m4'. The error output of SHELL-COMMAND is not a part of the expansion: it will appear along with the error output of `m4'. The macro `esyscmd' is recognized only with parameters. define(`foo', `FOO') => esyscmd(`echo foo') =>FOO => Note how the expansion of `esyscmd' keeps the trailing newline of the command, as well as using the newline that appeared after the macro. Just as with `syscmd', care must be exercised when sharing standard input between `m4' and the child process of `esyscmd'. 12.4 Exit status ================ To see whether a shell command succeeded, use `sysval': -- Builtin: sysval Expands to the exit status of the last shell command run with `syscmd' or `esyscmd'. Expands to 0 if no command has been run yet. syscmd(`false') => ifelse(sysval, `0', `zero', `non-zero') =>non-zero syscmd(`exit 2') => sysval =>2 syscmd(`true') => sysval =>0 esyscmd(`false') => ifelse(sysval, `0', `zero', `non-zero') =>non-zero esyscmd(`exit 2') => sysval =>2 esyscmd(`true') => sysval =>0 `sysval' results in 127 if there was a problem executing the command, for example, if the system-imposed argument length is exceeded, or if there were not enough resources to fork. It is not possible to distinguish between failed execution and successful execution that had an exit status of 127. On UNIX platforms, where it is possible to detect when command execution is terminated by a signal, rather than a normal exit, the result is the signal number shifted left by eight bits. dnl This test assumes kill is a shell builtin, and that signals are dnl recognizable. ifdef(`__unix__', , `errprint(` skipping: syscmd does not have unix semantics ')m4exit(`77')')dnl syscmd(`kill -13 $$') => sysval =>3328 esyscmd(`kill -9 $$') => sysval =>2304 12.5 Making temporary files =========================== Commands specified to `syscmd' or `esyscmd' might need a temporary file, for output or for some other purpose. There is a builtin macro, `maketemp', for making temporary file names: -- Builtin: maketemp (TEMPLATE) Expands to a name of a new, empty file, made from the string TEMPLATE, which should end with the string `XXXXXX'. The six `X' characters are then replaced with random data, in order to make the file name unique. The macro `maketemp' is recognized only with parameters. maketemp(`/tmp/fooXXXXXX') =>/tmp/fooa07346 Traditional implementations of `m4' replaced the trailing `X' sequence with the process id, without creating the file; meaning you only get one result no matter how many times you use maketemp on the same string. As of this release, POSIX is considering the addition of a new macro `mkstemp' that behaves like GNU `maketemp', so a future version of GNU M4 may have changes in this area. 13 Miscellaneous builtin macros ******************************* This chapter describes various builtins, that do not really belong in any of the previous chapters. 13.1 Printing error messages ============================ You can print error messages using `errprint': -- Builtin: errprint (MESSAGE, ...) Prints MESSAGE and the rest of the arguments on the standard error output, separated by spaces. The expansion of `errprint' is void. The macro `errprint' is recognized only with parameters. errprint(`Invalid arguments to forloop ') error-->Invalid arguments to forloop => A trailing newline is _not_ printed automatically, so it must be supplied as part of the argument, as in the example. BSD implementations of `m4' do append a trailing newline on each `errprint' call, while some other implementations only print the first argument. 13.2 Printing current location ============================== To make it possible to specify the location of an error, three utility builtins exist: -- Builtin: __file__ -- Builtin: __line__ -- Builtin: __program__ Expand to the quoted name of the current input file, the current input line number in that file, and the quoted name of the current invocation of `m4'. errprint(__program__:__file__:__line__: `input error ') error-->m4:stdin:1: input error => Line numbers start at 1 for each file. If the file was found due to the `-I' option or `M4PATH' environment variable, that is reflected in the file name. The syncline option (`-s', *note Invoking m4::), and the `f' and `l' flags of `debugmode' (*note Debug Levels::), also use this notion of current file and line. Redefining the three location macros has no effect on syncline, debug, or warning message output. Assume this example is run in the `checks' directory of the GNU M4 package, using `--include=../examples' in the command line to find the file `incl.m4' mentioned earlier: define(`foo', ``$0' called at __file__:__line__') => foo =>foo called at stdin:2 include(`incl.m4') =>Include file start =>foo called at ../examples/incl.m4:2 =>Include file end => Currently, all text wrapped with `m4wrap' (*note M4wrap::) behaves as though it came from line 0 of the file "". It is hoped that a future release of `m4' can overcome this limitation and remember which file invoked the call to `m4wrap'. The `__program__' macro behaves like `$0' in shell terminology. If you invoke `m4' through an absolute path or a link with a different spelling, rather than by relying on a `PATH' search for plain `m4', it will affect how `__program__' expands. The intent is that you can use it to produce error messages with the same formatting that `m4' produces internally. It can also be used within `syscmd' (*note Syscmd::) to pick the same version of `m4' that is currently running, rather than whatever version of `m4' happens to be first in `PATH'. 13.3 Exiting from `m4' ====================== If you need to exit from `m4' before the entire input has been read, you can use `m4exit': -- Builtin: m4exit ([CODE = `0']) Causes `m4' to exit, with exit status CODE. If CODE is left out, the exit status is zero. If CODE cannot be parsed, or is outside the range of 0 to 255, the exit status is one. No further input is read, and all wrapped and diverted text is discarded. A common use of this is to abort processing: -- Composite: fatal_error (MESSAGE) Abort processing with an error message and non-zero status. Prefix MESSAGE with details about where the error occurred, and print the resulting string to standard error. define(`fatal_error', `errprint(__program__:__file__:__line__`: fatal error: $* ')m4exit(`1')') => fatal_error(`this is a BAD one, buster') error-->m4:stdin:4: fatal error: this is a BAD one, buster After this macro call, `m4' will exit with exit status 1. This macro is only intended for error exits, since the normal exit procedures are not followed, e.g., diverted text is not undiverted, and saved text (*note M4wrap::) is not reread. (This macro has a subtle bug, when invoked from wrapped text. You should try to see if you can find it and correct it. *note Answers::) m4wrap(`This text is lost to `m4exit'.') => divert(`1') And so is this. divert => m4exit Note that it is still possible for the exit status to be different than what was requested by `m4exit'. If `m4' detects some other error, such as a write error on standard out, the exit status will be non-zero even if `m4exit' requested zero. If standard input is seekable, then the file will be positioned at the next unread character. If it is a pipe or other non-seekable file, then there are no guarantees how much data `m4' might have read into buffers, and thus discarded. 14 Fast loading of frozen state ******************************* Some bigger `m4' applications may be built over a common base containing hundreds of definitions and other costly initializations. Usually, the common base is kept in one or more declarative files, which files are listed on each `m4' invocation prior to the user's input file, or else each input file uses `include'. Reading the common base of a big application, over and over again, may be time consuming. GNU `m4' offers some machinery to speed up the start of an application using lengthy common bases. 14.1 Using frozen files ======================= Suppose a user has a library of `m4' initializations in `base.m4', which is then used with multiple input files: m4 base.m4 input1.m4 m4 base.m4 input2.m4 m4 base.m4 input3.m4 Rather than spending time parsing the fixed contents of `base.m4' every time, the user might rather execute: m4 -F base.m4f base.m4 once, and further execute, as often as needed: m4 -R base.m4f input1.m4 m4 -R base.m4f input2.m4 m4 -R base.m4f input3.m4 with the varying input. The first call, containing the `-F' option, only reads and executes file `base.m4', defining various application macros and computing other initializations. Once the input file `base.m4' has been completely processed, GNU `m4' produces on `base.m4f' a "frozen" file, that is, a file which contains a kind of snapshot of the `m4' internal state. Later calls, containing the `-R' option, are able to reload the internal state of `m4', from `base.m4f', _prior_ to reading any other input files. This means instead of starting with a virgin copy of `m4', input will be read after having effectively recovered the effect of a prior run. In our example, the effect is the same as if file `base.m4' has been read anew. However, this effect is achieved a lot faster. Only one frozen file may be created or read in any one `m4' invocation. It is not possible to recover two frozen files at once. However, frozen files may be updated incrementally, through using `-R' and `-F' options simultaneously. For example, if some care is taken, the command: m4 file1.m4 file2.m4 file3.m4 file4.m4 could be broken down in the following sequence, accumulating the same output: m4 -F file1.m4f file1.m4 m4 -R file1.m4f -F file2.m4f file2.m4 m4 -R file2.m4f -F file3.m4f file3.m4 m4 -R file3.m4f file4.m4 Some care is necessary because not every effort has been made for this to work in all cases. In particular, the trace attribute of macros is not handled, nor the current setting of `changeword'. Currently, `m4wrap' and `sysval' also have problems. Also, interactions for some options of `m4', being used in one call and not in the next, have not been fully analyzed yet. On the other end, you may be confident that stacks of `pushdef' definitions are handled correctly, as well as undefined or renamed builtins, and changed strings for quotes or comments. And future releases of GNU M4 will improve on the utility of frozen files. When an `m4' run is to be frozen, the automatic undiversion which takes place at end of execution is inhibited. Instead, all positively numbered diversions are saved into the frozen file. The active diversion number is also transmitted. A frozen file to be reloaded need not reside in the current directory. It is looked up the same way as an `include' file (*note Search Path::). If the frozen file was generated with a newer version of `m4', and contains directives that an older `m4' cannot parse, attempting to load the frozen file with option `-R' will cause `m4' to exit with status 63 to indicate version mismatch. 14.2 Frozen file format ======================= Frozen files are sharable across architectures. It is safe to write a frozen file on one machine and read it on another, given that the second machine uses the same or newer version of GNU `m4'. It is conventional, but not required, to give a frozen file the suffix of `.m4f'. These are simple (editable) text files, made up of directives, each starting with a capital letter and ending with a newline (). Wherever a directive is expected, the character `#' introduces a comment line; empty lines are also ignored if they are not part of an embedded string. In the following descriptions, each LEN refers to the length of the corresponding strings STR in the next line of input. Numbers are always expressed in decimal. There are no escape characters. The directives are: `C LEN1 , LEN2 STR1 STR2 ' Uses STR1 and STR2 as the begin-comment and end-comment strings. If omitted, then `#' and are the comment delimiters. `D NUMBER, LEN STR ' Selects diversion NUMBER, making it current, then copy STR in the current diversion. NUMBER may be a negative number for a non-existing diversion. To merely specify an active selection, use this command with an empty STR. With 0 as the diversion NUMBER, STR will be issued on standard output at reload time. GNU `m4' will not produce the `D' directive with non-zero length for diversion 0, but this can be done with manual edits. This directive may appear more than once for the same diversion, in which case the diversion is the concatenation of the various uses. If omitted, then diversion 0 is current. `F LEN1 , LEN2 STR1 STR2 ' Defines, through `pushdef', a definition for STR1 expanding to the function whose builtin name is STR2. If the builtin does not exist (for example, if the frozen file was produced by a copy of `m4' compiled with changeword support, but the version of `m4' reloading was compiled without it), the reload is silent, but any subsequent use of the definition of STR1 will result in a warning. This directive may appear more than once for the same name, and its order, along with `T', is important. If omitted, you will have no access to any builtins. `Q LEN1 , LEN2 STR1 STR2 ' Uses STR1 and STR2 as the begin-quote and end-quote strings. If omitted, then ``' and `'' are the quote delimiters. `T LEN1 , LEN2 STR1 STR2 ' Defines, though `pushdef', a definition for STR1 expanding to the text given by STR2. This directive may appear more than once for the same name, and its order, along with `F', is important. `V NUMBER ' Confirms the format of the file. `m4' 1.4.7 only creates and understands frozen files where NUMBER is 1. This directive must be the first non-comment in the file, and may not appear more than once. 15 Compatibility with other versions of `m4' ******************************************** This chapter describes the differences between this implementation of `m4', and the implementation found under UNIX, notably System V, Release 3. There are also differences in BSD flavors of `m4'. No attempt is made to summarize these here. 15.1 Extensions in GNU `m4' =========================== This version of `m4' contains a few facilities that do not exist in System V `m4'. These extra facilities are all suppressed by using the `-G' command line option (*note Invoking m4::), unless overridden by other command line options. * In the `$'N notation for macro arguments, N can contain several digits, while the System V `m4' only accepts one digit. This allows macros in GNU `m4' to take any number of arguments, and not only nine (*note Arguments::). This means that `define(`foo', `$11')' is ambiguous between implementations. To portably choose between grabbing the first parameter and appending 1 to the expansion, or grabbing the eleventh parameter, you can do the following: define(`a1', `A1') => dnl First argument, concatenated with 1 define(`_1', `$1')define(`first1', `_1($@)1') => dnl Eleventh argument, portable define(`_9', `$9')define(`eleventh', `_9(shift(shift($@)))') => dnl Eleventh argument, GNU style define(`Eleventh', `$11') => first1(`a', `b', `c', `d', `e', `f', `g', `h', `i', `j', `k') =>A1 eleventh(`a', `b', `c', `d', `e', `f', `g', `h', `i', `j', `k') =>k Eleventh(`a', `b', `c', `d', `e', `f', `g', `h', `i', `j', `k') =>k * The `divert' (*note Divert::) macro can manage more than 9 diversions. GNU `m4' treats all positive numbers as valid diversions, rather than discarding diversions greater than 9. * Files included with `include' and `sinclude' are sought in a user specified search path, if they are not found in the working directory. The search path is specified by the `-I' option and the `M4PATH' environment variable (*note Search Path::). * Arguments to `undivert' can be non-numeric, in which case the named file will be included uninterpreted in the output (*note Undivert::). * Formatted output is supported through the `format' builtin, which is modeled after the C library function `printf' (*note Format::). * Searches and text substitution through regular expressions are supported by the `regexp' (*note Regexp::) and `patsubst' (*note Patsubst::) builtins. * The output of shell commands can be read into `m4' with `esyscmd' (*note Esyscmd::). * There is indirect access to any builtin macro with `builtin' (*note Builtin::). * Macros can be called indirectly through `indir' (*note Indir::). * The name of the program, the current input file, and the current input line number are accessible through the builtins `__program__', `__file__', and `__line__' (*note Location::). * The format of the output from `dumpdef' and macro tracing can be controlled with `debugmode' (*note Debug Levels::). * The destination of trace and debug output can be controlled with `debugfile' (*note Debug Output::). In addition to the above extensions, GNU `m4' implements the following command line options: `-F', `-G', `-I', `-L', `-R', `-V', `-W', `-d', `-i', `-l', `--debugfile' and `-t'. *Note Invoking m4::, for a description of these options. Also, the debugging and tracing facilities in GNU `m4' are much more extensive than in most other versions of `m4'. 15.2 Facilities in System V `m4' not in GNU `m4' ================================================ The version of `m4' from System V contains a few facilities that have not been implemented in GNU `m4' yet. Additionally, POSIX requires some behaviors that GNU `m4' has not implemented yet. Relying on these behaviors is non-portable, as a future release of GNU `m4' may change. * System V `m4' supports multiple arguments to `defn', and POSIX requires it. This is not yet implemented in GNU `m4'. Unfortunately, this means it is not possible to mix builtins and other text into a single macro; a helper macro is required. * POSIX requires an application to exit with non-zero status if it wrote an error message to stderr. This has not yet been consistently implemented for the various builtins that are required to issue an error (such as `include' (*note Include::) when a file is unreadable, `eval' (*note Eval::) when an argument cannot be parsed, or using `m4exit' (*note M4exit::) with a non-numeric argument). * Some traditional implementations only allow reading standard input once, but GNU `m4' correctly handles multiple instances of `-' on the command line. * POSIX requires `m4wrap' (*note M4wrap::) to act in FIFO (first-in, first-out) order, but GNU `m4' currently uses LIFO order. Furthermore, POSIX states that only the first argument to `m4wrap' is saved for later evaluation, bug GNU `m4' saves and processes all arguments, with output separated by spaces. However, it is possible to emulate POSIX behavior by including the file `examples/wrapfifo.m4' from the distribution: undivert(`wrapfifo.m4')dnl =>dnl Redefine m4wrap to have FIFO semantics. =>define(`_m4wrap_level', `0')dnl =>define(`m4wrap', =>`ifdef(`m4wrap'_m4wrap_level, => `define(`m4wrap'_m4wrap_level, => defn(`m4wrap'_m4wrap_level)`$1')', => `builtin(`m4wrap', `define(`_m4wrap_level', => incr(_m4wrap_level))dnl =>m4wrap'_m4wrap_level)dnl =>define(`m4wrap'_m4wrap_level, `$1')')')dnl include(`wrapfifo.m4') => m4wrap(`a`'m4wrap(`c ', `d')')m4wrap(`b') => ^D =>abc * POSIX requires that all builtins that require arguments, but are called without arguments, behave as though empty strings had been passed. For example, `a`'define`'b' would expand to `ab'. But GNU `m4' ignores certain builtins if they have missing arguments, giving `adefineb' for the above example. * Traditional implementations handle `define(`f',`1')' (*note Define::) by undefining the entire stack of previous definitions, and if doing `undefine(`f')' first. GNU `m4' replaces just the top definition on the stack, as if doing `popdef(`f')' followed by `pushdef(`f',`1')'. * POSIX requires `syscmd' (*note Syscmd::) to evaluate command output for macro expansion, but this appears to be a mistake in POSIX since traditional implementations did not do this. GNU `m4' follows traditional behavior in `syscmd', and provides the extension `esyscmd' that provides the POSIX semantics. * POSIX requires `maketemp' (*note Maketemp::) to replace the trailing `X' characters with the `m4' process id, giving the same result on identical input, without creating any files, which leaves the door open for a data race in which other processes can create a file by the same name. GNU `m4' actually creates a temporary file for each invocation of `maketemp', which means that the output of the macro is different even if the input is identical. * POSIX requires `changequote(ARG)' (*note Changequote::) to use newline as the close quote, but GNU `m4' uses `'' as the close quote. Meanwhile, some traditional implementations use ARG as the close quote, making it impossible to nest quotes. For predictable results, never call changequote with just one argument. * Some implementations of `m4' give macros a higher precedence than comments when parsing, meaning that if the start delimiter given to `changecom' (*note Changecom::) starts with a macro name, comments are effectively disabled. POSIX does not specify what the precedence is, so the GNU `m4' parser recognizes comments, then macros, then quoted strings. * Traditional implementations allow argument collection, but not string and comment processing, to span file boundaries. Thus, if `a.m4' contains `len(', and `b.m4' contains `abc)', `m4 a.m4 b.m4' outputs `3' with traditional `m4', but gives an error message that the end of file was encountered inside a macro with GNU `m4'. On the other hand, traditional implementations do end of file processing for files included with `include' or `sinclude' (*note Include::), while GNU `m4' seamlessly integrates the content of those files. Thus `include(`a.m4')include(`b.m4')' will output `3' instead of giving an error. * Traditional `m4' treats `traceon' (*note Trace::) without arguments as a global variable, independent of named macro tracing. Also, once a macro is undefined, named tracing of that macro is lost. On the other hand, when GNU `m4' encounters `traceon' without arguments, it turns tracing on for all existing definitions at the time, but does not trace future definitions; `traceoff' without arguments turns tracing off for all definitions regardless of whether they were also traced by name; and tracing by name, such as with `-tfoo' at the command line or `traceon(`foo')' in the input, is an attribute that is preserved even if the macro is currently undefined. * POSIX requires `eval' (*note Eval::) to treat all operators with the same precedence as C. However, GNU `m4' currently follows the traditional precedence of other `m4' implementations, where bitwise and logical negation (`~' and `!') have lower precedence than equality operators, rather than equal precedence with other unary operators. Use explicit parentheses to ensure proper precedence. As extensions to POSIX, GNU `m4' treats the shift operators `<<' and `>>' as well-defined on signed integers (even though they are not in C), and adds the exponentiation operator `**'. * POSIX requires `translit' (*note Translit::) to treat each character of the second and third arguments literally, but GNU `m4' treats `-' as a range operator. * POSIX requires `m4' to honor the locale environment variables of `LANG', `LC_ALL', `LC_CTYPE', `LC_MESSAGES', and `NLSPATH', but this has not yet been implemented in GNU `m4'. 15.3 Other incompatibilities ============================ There are a few other incompatibilities between this implementation of `m4', and the System V version. * GNU `m4' implements sync lines differently from System V `m4', when text is being diverted. GNU `m4' outputs the sync lines when the text is being diverted, and System V `m4' when the diverted text is being brought back. The problem is which lines and file names should be attached to text that is being, or has been, diverted. System V `m4' regards all the diverted text as being generated by the source line containing the `undivert' call, whereas GNU `m4' regards the diverted text as being generated at the time it is diverted. The sync line option is used mostly when using `m4' as a front end to a compiler. If a diverted line causes a compiler error, the error messages should most probably refer to the place where the diversion were made, and not where it was inserted again. * GNU `m4' makes no attempt at prohibiting self-referential definitions like: define(`x', `x') => define(`x', `x ') => There is nothing inherently wrong with defining `x' to return `x'. The wrong thing is to expand `x' unquoted. In `m4', one might use macros to hold strings, as we do for variables in other programming languages, further checking them with: ifelse(defn(`HOLDER'), `VALUE', ...) In cases like this one, an interdiction for a macro to hold its own name would be a useless limitation. Of course, this leaves more rope for the GNU `m4' user to hang himself! Rescanning hangs may be avoided through careful programming, a little like for endless loops in traditional programming languages. 16 Correct version of some examples *********************************** Some of the examples in this manuals are buggy, for demonstration purposes. Correctly working macros are presented here. The `exch' macro (*note Arguments::) as presented requires clients to double quote their arguments. A nicer definition, which lets clients follow the rule of thumb of one level of quoting per level of parentheses, involves adding quotes in the definition of `exch', as follows: define(`exch', ``$2', `$1'') => define(exch(`expansion text', `macro')) => macro =>expansion text The `cleardivert' macro (*note Cleardiv::) cannot, as it stands, be called without arguments to clear all pending diversions. That is because using undivert with an empty string for an argument is different than using it with no arguments at all. Compare the earlier definition with one that takes the number of arguments into account: define(`cleardivert', `pushdef(`_n', divnum)divert(`-1')undivert($@)divert(_n)popdef(`_n')') => divert(`1')one divert => cleardivert => undivert =>one => define(`cleardivert', `pushdef(`_num', divnum)divert(`-1')ifelse(`$#', `0', `undivert`'', `undivert($@)')divert(_num)popdef(`_num')') => divert(`2')two divert => cleardivert => undivert => The `fatal_error' macro (*note M4exit::) does not quite match the format of internal error messages when invoked inside wrapped text, due to the current limitations of `__file__' (*note Location::) when invoked inside `m4wrap'. Since `m4' omits the file and line number from its warning messages when there is no current file (or equivalently, when the current line is 0, since all files start at line 1), a better implementation would be: define(`fatal_error', `errprint(__program__:ifelse(__line__, `0', `', `__file__:__line__:')` fatal error: $* ')m4exit(`1')') => m4wrap(`divnum(`demo of internal message') fatal_error(`inside wrapped text')') => ^D error-->m4: Warning: excess arguments to builtin `divnum' ignored =>0 error-->m4: fatal error: inside wrapped text Appendix A How to make copies of this manual ******************************************** A.1 GNU Free Documentation License ================================== Version 1.2, November 2002 Copyright (C) 2000,2001,2002 Free Software Foundation, Inc. 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. 0. 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Appendix B Indices of concepts and macros ***************************************** B.1 Index for many concepts =========================== arguments to macros: See 3.3. (line 812) Arguments to macros: See 4.2. (line 979) arguments to macros, special: See 4.3. (line 1031) arguments, quoted macro: See 3.4. (line 861) arithmetic: See 11. (line 3090) arrays: See 4.1. (line 959) builtins, indirect call of: See 4.8. (line 1396) call of builtins, indirect: See 4.8. (line 1396) call of macros, indirect: See 4.7. (line 1354) changing comment delimiters: See 7.3. (line 2130) changing the quote delimiters: See 7.2. (line 1999) characters, translating: See 10.5. (line 2906) command line, file names on the: See 1.3. (line 458) command line, macro definitions on the: See 1.3. (line 301) command line, options: See 1.3. (line 233) commands, exit status from shell: See 12.4. (line 3404) commands, running shell: See 12. (line 3271) commands, running UNIX: See 12. (line 3271) comment delimiters, changing: See 7.3. (line 2130) comments: See 2.3. (line 608) comments, copied to output: See 7.3. (line 2153) comparing strings: See 5.2. (line 1488) compatibility: See 15. (line 3768) conditionals: See 5.1. (line 1465) controlling debugging output: See 6.3. (line 1822) counting loops: See 5.3. (line 1617) debugging output, controlling: See 6.3. (line 1822) debugging output, saving: See 6.4. (line 1911) decrement operator: See 11.1. (line 3097) defining new macros: See 4. (line 906) definitions, displaying macro: See 6.1. (line 1690) deleting macros: See 4.4. (line 1147) deleting whitespace in input: See 7.1. (line 1951) discarding diverted text: See 9.4. (line 2745) displaying macro definitions: See 6.1. (line 1690) diversion numbers: See 9.3. (line 2725) diverted text, discarding: See 9.4. (line 2745) diverting output to files: See 9.1. (line 2563) dumping into frozen file: See 14.1. (line 3631) error messages, printing: See 13.1. (line 3494) evaluation, of integer expressions: See 11.2. (line 3122) executing shell commands: See 12. (line 3271) executing UNIX commands: See 12. (line 3271) exit status from shell commands: See 12.4. (line 3404) exiting from m4: See 13.3. (line 3568) expansion of macros: See 3.5. (line 889) expansion, tracing macro: See 6.2. (line 1732) expressions, evaluation of integer: See 11.2. (line 3122) extracting substrings: See 10.4. (line 2877) fast loading of frozen files: See 14.1. (line 3631) FDL, GNU Free Documentation License: See A.1. (line 4110) file format, frozen file: See 14.2. (line 3708) file inclusion <1>: See 9.2. (line 2704) file inclusion: See 8. (line 2452) file names, on the command line: See 1.3. (line 458) files, diverting output to: See 9.1. (line 2563) files, names of temporary: See 12.5. (line 3463) for loops: See 5.3. (line 1617) formatted output: See 10.7. (line 3035) frozen file format: See 14.2. (line 3708) frozen files for fast loading: See 14.1. (line 3631) GNU extensions <1>: See 4.8. (line 1396) GNU extensions <2>: See 9.2. (line 2704) GNU extensions <3>: See 15.1. (line 3778) GNU extensions <4>: See 10.6. (line 2949) GNU extensions <5>: See 8.2. (line 2528) GNU extensions <6>: See 12.3. (line 3376) GNU extensions <7>: See 14.1. (line 3631) GNU extensions <8>: See 6.4. (line 1911) GNU extensions <9>: See 10.3. (line 2822) GNU extensions <10>: See 4.2. (line 1005) GNU extensions <11>: See 10.7. (line 3035) GNU extensions <12>: See 4.7. (line 1354) GNU extensions <13>: See 4.1. (line 948) GNU extensions: See 6.3. (line 1875) included files, search path for: See 8.2. (line 2528) inclusion, of files <1>: See 9.2. (line 2704) inclusion, of files: See 8. (line 2452) increment operator: See 11.1. (line 3097) indirect call of builtins: See 4.8. (line 1396) indirect call of macros: See 4.7. (line 1354) initialization, frozen states: See 14.1. (line 3631) input tokens: See 2. (line 565) input, saving: See 7.5. (line 2383) integer arithmetic: See 11. (line 3090) integer expression evaluation: See 11.2. (line 3122) length of strings: See 10.1. (line 2784) lexical structure of words: See 7.4. (line 2227) License: See Appendix A. (line 4107) local variables: See 4.6. (line 1343) loops: See 5.3. (line 1577) loops, counting: See 5.3. (line 1617) macro definitions, on the command line: See 1.3. (line 301) macro expansion, tracing: See 6.2. (line 1732) macro invocation: See 3.1. (line 687) macros, arguments to <1>: See 4.2. (line 979) macros, arguments to: See 3.3. (line 812) macros, displaying definitions: See 6.1. (line 1690) macros, expansion of: See 3.5. (line 889) macros, how to define new: See 4. (line 906) macros, how to delete: See 4.4. (line 1147) macros, how to rename: See 4.5. (line 1187) macros, indirect call of: See 4.7. (line 1354) macros, quoted arguments to: See 3.4. (line 861) macros, recursive: See 5.3. (line 1573) macros, special arguments to: See 4.3. (line 1031) macros, temporary redefinition of: See 4.6. (line 1274) messages, printing error: See 13.1. (line 3494) multibranches: See 5.2. (line 1548) names: See 2.1. (line 578) options, command line: See 1.3. (line 233) output, diverting to files: See 9.1. (line 2563) output, formatted: See 10.7. (line 3035) output, saving debugging: See 6.4. (line 1911) pattern substitution: See 10.6. (line 2949) platform macro: See 12.1. (line 3309) platform macros: See 12.1. (line 3284) POSIXLY_CORRECT: See 1.3. (line 233) printing error messages: See 13.1. (line 3494) quote delimiters, changing the: See 7.2. (line 1999) quoted macro arguments: See 3.4. (line 861) quoted string: See 2.2. (line 589) recursive macros: See 5.3. (line 1573) redefinition of macros, temporary: See 4.6. (line 1274) regular expressions <1>: See 10.3. (line 2822) regular expressions: See 10.6. (line 2949) reloading a frozen file: See 14.1. (line 3631) renaming macros: See 4.5. (line 1187) running shell commands: See 12. (line 3271) running UNIX commands: See 12. (line 3271) saving debugging output: See 6.4. (line 1911) saving input: See 7.5. (line 2383) search path for included files: See 8.2. (line 2528) shell commands, exit status from: See 12.4. (line 3404) shell commands, running: See 12. (line 3271) special arguments to macros: See 4.3. (line 1031) status of shell commands: See 12.4. (line 3404) status, setting m4 exit: See 13.3. (line 3568) strings, length of: See 10.1. (line 2784) substitution by regular expression: See 10.6. (line 2949) substrings, extracting: See 10.4. (line 2877) temporary file names: See 12.5. (line 3463) temporary redefinition of macros: See 4.6. (line 1274) tokens: See 2. (line 565) tracing macro expansion: See 6.2. (line 1732) translating characters: See 10.5. (line 2906) undefining macros: See 4.4. (line 1147) UNIX commands, exit status from: See 12.4. (line 3404) UNIX commands, running: See 12. (line 3271) variables, local: See 4.6. (line 1343) words, lexical structure of: See 7.4. (line 2227) B.2 Index for all `m4' macros ============================= References are exclusively to the places where a builtin is introduced the first time. __file__: See 13.2. (line 3520) __gnu__: See 12.1. (line 3290) __line__: See 13.2. (line 3521) __os2__: See 12.1. (line 3291) __program__: See 13.2. (line 3522) __unix__: See 12.1. (line 3293) __windows__: See 12.1. (line 3295) builtin: See 4.8. (line 1399) capitalize: See 10.6. (line 2997) changecom: See 7.3. (line 2134) changequote: See 7.2. (line 2003) changeword: See 7.4. (line 2244) cleardivert: See 9.4. (line 2765) debugfile: See 6.4. (line 1916) debugmode: See 6.3. (line 1879) decr: See 11.1. (line 3102) define: See 4.1. (line 917) defn: See 4.5. (line 1191) divert: See 9.1. (line 2566) divnum: See 9.3. (line 2728) dnl: See 7.1. (line 1954) downcase: See 10.6. (line 2996) dumpdef: See 6.1. (line 1694) errprint: See 13.1. (line 3497) esyscmd: See 12.3. (line 3379) eval: See 11.2. (line 3125) example: See 1.5. (line 532) fatal_error: See 13.3. (line 3580) forloop: See 5.3. (line 1620) format: See 10.7. (line 3038) ifdef: See 5.1. (line 1469) ifelse: See 5.2. (line 1494) include: See 8.1. (line 2460) incr: See 11.1. (line 3101) index: See 10.2. (line 2802) indir: See 4.7. (line 1357) len: See 10.1. (line 2787) m4exit: See 13.3. (line 3572) m4wrap: See 7.5. (line 2391) maketemp: See 12.5. (line 3468) os2: See 12.1. (line 3292) patsubst: See 10.6. (line 2952) popdef: See 4.6. (line 1280) pushdef: See 4.6. (line 1279) regexp: See 10.3. (line 2825) reverse: See 5.3. (line 1599) shift: See 5.3. (line 1584) sinclude: See 8.1. (line 2461) substr: See 10.4. (line 2880) syscmd: See 12.2. (line 3338) sysval: See 12.4. (line 3407) traceoff: See 6.2. (line 1737) traceon: See 6.2. (line 1736) translit: See 10.5. (line 2909) undefine: See 4.4. (line 1150) undivert: See 9.2. (line 2636) unix: See 12.1. (line 3294) upcase: See 10.6. (line 2995) windows: See 12.1. (line 3296)