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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.