Re^3: Running a C program from Perl

$result can be non-empty i.e. iff $bin generates anything to STDERR .

If the command in backticks generates any output on its own stderr, that goes directly to the perl script's STDERR, and does not get captured/assigned by the backticks -- in the OP case, $result will still be empty, because backticks only return what went to the command's stdout.

Now, if the command being run in backticks included redirection of stderr to stdout (and no subsequent redirection of stdout to some file), then backticks would capture any stderr content along with any stdout -- e.g. if your backticks are executing a bourne-style shell, the following would generally include some sort of error message to the perl variable, along with any matching lines found by grep in ~/.bashrc:

  my $result = `grep PATH ~/.bashrc /no/such/file 2>&1`
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Re^4: Running a C program from Perl by Bloodnok (Vicar) on May 27, 2009 at 09:31 UTC
Hmmm, I think it looks like I and to some extent you, are barking up the wrong tree (well on linux & AIX anyway) - consider the following behaviour exhibited by both Linux 2.6.28-11-generic and AIX 5.3: user@unforgiven:~$ egrepa bash: egrepa: command not found user@unforgiven:~$ egrepa >/dev/null bash: egrepa: command not found user@unforgiven:~$ egrepa >/dev/null 2>&1 user@unforgiven:~$ perl -e '$res = `egrepa 2>&1`; print $res' user@unforgiven:~$ [download] Personally, I would expect the one-liner to print bash: egrepa: command not found - as it does if entered from command line - but doesn't. If, however, as you suggest, a valid command is used with invalid opts, then the re-direction works as expected and the error is seen (on both platforms). A user level that continues to overstate my experience :-))	[reply] [d/l]
Re^5: Running a C program from Perl by ikegami (Patriarch) on May 27, 2009 at 13:45 UTC
Personally, I would expect the one-liner to print bash: egrepa: command not found - as it does if entered from command line - but doesn't. The shell was never invoked, so how can it display an error message? It's up to you to do your own error checking. $ perl -e'$res = `egrepa 2>&1`; print "$?:$!\n"; print $res' -1:No such file or directory (( Perl tried to execute egrepa, couldn't, and returned an error. Perl doesn't output error messages for you. )) $ perl -e'$res = `egrepa "" 2>&1`; print "$?:$!\n"; print $res' 32512: sh: egrepa: command not found (( Perl sees a shell command, and successfully executed the shell. The shell couldn't execute egrapa "", so it displayed and returned an error. )) [download]	[reply] [d/l]