How can I get the CPU time for a perl system call?

Question

I have a perl script that calls external executables using system(). I would like to measure the CPU seconds taken by these external programs. Ideally, I would like

Answer 1

You can use Capture::Tiny to capture the STDOUT and STDERR of pretty much anything in Perl.

use Capture::Tiny 'capture';

my ($stdout, $stderr, $exit) = capture { system "time ls" };

print $stderr;

For some reason the output is missing some whitespace on my system, but is clear enough to parse out what you need.

0.00user 0.00system 0:00.00elapsed 0%CPU (0avgtext+0avgdata 2272maxresident)k
0inputs+8outputs (0major+111minor)pagefaults 0swaps

Answer 2

$ time ( ls ) 2> er ## works
$ perl -e 'system("time (ls)")'
sh: 1: Syntax error: word unexpected (expecting ")")

The problem is that in first case, your shell is probably /bin/bash whereas in second case it is /bin/sh. If you want to run your command with another shell, you could use system LIST form:

system("/bin/bash", "-c", "time(ls)")

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Note 1: There's PERL5SHELL environmnet value, but that seems to take effect only on Win32.

Note 2: If you want to measure CPU time of child process, you could use Unix::Getrusage or BSD::Resource modules.

Answer 3

You've tested the command with bash, but you passed it to sh.

system("time (ls)")

is short for

system("/bin/sh", "-c", "time (ls)")

but you want

system("/bin/bash", "-c", "time (ls)")