Perl: checking if makedepend is available without using File::Which
Posted by jpluimers on 2016/08/25
Long lasting open source projects often use makedepend to amend Makefiles with C header dependencies.
However, makedepend is old, not available on some systems (like Mac OS X or Windows) and can have different behaviour than the C compiler on those systems. The alternative usually is the -M switch on the C compiler.
In practice, either makedepend, or the alternative is available, so when prepping for a build you have to choose which one to use.
Some of those open source projects use Perl as a bootstrapper. I’ll write more about those boots trappers in the future, but first lets go back to the post title:
First detecting the availability of makedepend from Perl without relying on File::Which which isn’t installed by default on systems having Perl so a gated check-in build like this Travis build fails.
The trick I use is Perl backticks (aka qx) to try and execute makedepend merging the output of both stdout and stderr (using 2>&1 which is available on most shells). If there is no output, then the result is undef which means makedepend is not available.
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| # http://perldoc.perl.org/perlop.html#Quote-Like-Operators | |
| # ensure to take the stdout and stderror so we get output like this: | |
| # 'makedepend: error: cannot open "Makefile.makedepend" | |
| #'. | |
| my $makedepend_output = `makedepend -f Makefile.makedepend 2>&1`; | |
| if (!$makedepend_output) | |
| { | |
| print "No makedepend executable found on your path.\n"; | |
| } | |
| else | |
| { | |
| print "Output of makedepend: '$makedepend_output'.\n"; | |
| } |
–jeroen
via:
- What’s the difference between Perl’s backticks, system, and exec? – Stack Overflow.
- Perl booleans, negation (and how to explain it)? – Stack Overflow.
- undef, the initial value and the defined function of Perl.
The Wiert Corner - irregular stream of stuff 
Modifying openssl to build on Mac without makedepend: using cc -M/gcc -M/clang -M « The Wiert Corner – irregular stream of stuff said
[…] matching, the main Perl thing was to find if makedepend exists as an executable on the path. I wrote about that before, as the File::Which solution that I started with isn’t available in all Perl […]