Multiple Files - Finding Files

Sometimes you need to process files one of the time. But usually this is not necessary, and, it is faster to run a command on as many files as possible at a time, rather than once per file. Doing this saves on the time it takes to start up the command each time.

The -execdir and -exec actions have variants that build command lines containing as many matched files as possible.

— Action: -execdir command {} +

This works as for -execdir command ;, except that the {} at the end of the command is expanded to a list of names of matching files. This expansion is done in such a way as to avoid exceeding the maximum command line length available on the system. Only one {} is allowed within the command, and it must appear at the end, immediately before the +. A + appearing in any position other than immediately after {} is not considered to be special (that is, it does not terminate the command).

— Action: -exec command {} +

This insecure variant of the -execdir action is specified by POSIX. The main difference is that the command is executed in the directory from which find was invoked, meaning that {} is expanded to a relative path starting with the name of one of the starting directories, rather than just the basename of the matched file.

Before find exits, any partially-built command lines are executed. This happens even if the exit was caused by the -quit action. However, some types of error (for example not being able to invoke stat() on the current directory) can cause an immediate fatal exit. In this situation, any partially-built command lines will not be invoked (this prevents possible infinite loops).

Another, but less secure, way to run a command on more than one file at once, is to use the xargs command, which is invoked like this:

xargs normally reads arguments from the standard input. These arguments are delimited by blanks (which can be protected with double or single quotes or a backslash) or newlines. It executes the command (default is /bin/echo) one or more times with any initial-arguments followed by arguments read from standard input. Blank lines on the standard input are ignored.

Instead of blank-delimited names, it is safer to use find -print0 or find -fprint0 and process the output by giving the -0 or --null option to GNU xargs, GNU tar, GNU cpio, or perl. The locate command also has a -0 or --null option which does the same thing.

You can use shell command substitution (backquotes) to process a list of arguments, like this:

However, that method produces an error if the length of the .c file names exceeds the operating system's command-line length limit. xargs avoids that problem by running the command as many times as necessary without exceeding the limit:

However, if the command needs to have its standard input be a terminal (less, for example), you have to use the shell command substitution method or use the --arg-file option of xargs.

The xargs command will process all its input, building command lines and executing them, unless one of the commands exits with a status of 255 (this will cause xargs to issue an error message and stop) or it reads a line contains the end of file string specified with the --eof option.

3.3.2 Multiple Files