coreutils timeout simulate on perl - perl

Question

I trying to make replacement for timeout using perl (need in centos5)
here the script:
#!/usr/bin/perl
use strict;
my $pid=$$;
my $timeout=shift;
my #args=#ARGV;
eval {
local $SIG{ALRM} = sub {
print "Timed OUT!\n";
exit 142;
kill 9,$pid;
};
alarm($timeout);
system(#args);
};
exit $?;
while testing it I found:
Here all fine
time /tmp/timeout 3 sleep 6
Timed OUT!
real 0m3.007s
user 0m0.000s
sys 0m0.004s
but here all bad
time echo `/tmp/timeout 3 sleep 6`
Timed OUT!
real 0m6.009s
user 0m0.000s
sys 0m0.004s
on my debian system I tested with /usr/bin/timeout:
time echo `/usr/bin/timeout 3 sleep 6`
real 0m3.004s
user 0m0.000s
sys 0m0.000s
So the questions
why the perl script work so strange ?
is there any real working way to have timeout writen on perl which will work the same as binary timeout ?
please note, that I know about /usr/share/doc/bash-3.2/scripts/timeout and I also found that it acts the same as my perl approach
also please note that I can't install modules from CPAN on the server targeted for this script
i tried with exec() but in that case it does not handle signal in sub.
UPD
with the script from #rhj (had to fix a little)
#!/usr/bin/perl
use strict;
use warnings;
my $PID=$$;
my $timeout=shift;
my #args=#ARGV;
my $pid = fork();
defined $pid or die "fork: $!";
$pid == 0 && exec(#args);
my $timed_out = 0;
$SIG{ALRM} = sub { $timed_out = 1; die; };
alarm $timeout;
eval { waitpid $pid, 0 };
alarm 0;
if ($timed_out) {
print "Timed out!\n";
kill 9, $pid;
kill 9, $PID;
}
elsif ($#) {
warn "error: $#\n";
}
it pass above test but fail in the case of calling external script:
run_script
#!/bin/sh
sleep 6
test.sh
#!/bin/sh
a=`./timeout.pl 2 ./run_script.sh`
output
$ time ./test.sh
real 0m6.020s
user 0m0.004s
sys 0m0.008s

Answer 1

This version should always work:
#!/usr/bin/perl
use strict;
use warnings;
my $pid=$$;
my $timeout=shift;
my #args=#ARGV;
my $pid = fork();
defined $pid or die "fork: $!";
$pid == 0 && exec(#args);
my $timed_out = 0;
$SIG{ALRM} = sub { $timed_out = 1; die; };
alarm $timeout;
eval { waitpid $pid, 0 };
alarm 0;
if ($timed_out) {
print "Timed out!\n";
kill 9, $pid;
}
elsif ($#) {
warn "error: $#\n";
}
It does not handle an error in the exec() call, though.

Answer 2

Had to make it with IPC::Cmd;
#!/usr/bin/perl -w
use strict;
use IPC::Cmd qw(run_forked);
my $timeout=shift;
my $stdout;
my $hashref = run_forked(#ARGV, { timeout => $timeout});
print $hashref->{'stdout'};
print STDERR $hashref->{'stderr'};
if ($hashref->{'timeout'}) {
print STDERR "Timed out!\n";
exit 142;
}
exit $hashref->{'exit_code'};
the bad thing that I had to install IPC::Cmd using rpmforge.