File: autoconf.info,  Node: ifnames Invocation,  Next: autoconf Invocation,  Prev: autoscan Invocation,  Up: Making configure Scripts

3.3 Using ‘ifnames’ to List Conditionals
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‘ifnames’ can help you write ‘configure.ac’ for a software package.  It
prints the identifiers that the package already uses in C preprocessor
conditionals.  If a package has already been set up to have some
portability, ‘ifnames’ can thus help you figure out what its ‘configure’
needs to check for.  It may help fill in some gaps in a ‘configure.ac’
generated by ‘autoscan’ (*note autoscan Invocation::).

   ‘ifnames’ scans all of the C source files named on the command line
(or the standard input, if none are given) and writes to the standard
output a sorted list of all the identifiers that appear in those files
in ‘#if’, ‘#elif’, ‘#ifdef’, or ‘#ifndef’ directives.  It prints each
identifier on a line, followed by a space-separated list of the files in
which that identifier occurs.

‘ifnames’ accepts the following options:

‘--help’
‘-h’
     Print a summary of the command line options and exit.

‘--version’
‘-V’
     Print the version number of Autoconf and exit.