ifnames - Extract CPP conditionals from a set of files
ifnames [OPTION]... [FILE]...
Scan all of the C source FILES (or the standard input, if none are given) and write to the standard output a sorted list of all the identifiers that appear in those files in '#if', '#elif', '#ifdef', or '#ifndef' directives. Print each identifier on a line, followed by a space-separated list of the files in which that identifier occurs.
print this help, then exit
print version number, then exit
Written by David J. MacKenzie and Paul Eggert.
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autoconf(1), automake(1), autoreconf(1), autoupdate(1), autoheader(1), autoscan(1), config.guess(1), config.sub(1), ifnames(1), libtool(1).
The full documentation for ifnames is maintained as a Texinfo manual. If the info and ifnames programs are properly installed at your site, the command
info ifnames
should give you access to the complete manual.