You'll probably want to use fork/exec for this. You'll probably find the perlipc pod useful. Here's a small, very lightly tested example to get you going. Good luck!

#!/usr/bin/perl -l
use strict;
use warnings;

spawn(5, "/tmp/cmd.pl");

sub spawn
{
    my ($timeout, @cmd) = @_;

    defined( my $child_pid = fork ) or die "fork: $!";

    if ($child_pid)
    {
        # parent
        eval
        {
            local $SIG{ALRM} = sub { timeout($child_pid); };
            alarm $timeout;
            waitpid $child_pid, 0;
            alarm 0;
        };

        if ($@)
        {
            print "oops: $@";
        }
    }
    else
    {
        # child
        exec @cmd or die "exec: $!";
    }
}

sub timeout
{
    my ($pid) = @_;
    kill 'TERM' => $pid;
    waitpid $pid, 0;
    die "reaped $pid\n";
}
[download]

Hi edan,

Thanks very much for this example code, I have taken it, adapted it a bit and it works exactly how I wanted.

Thanks again,

Richard Thomas.

Hi edan,

There is just one bit left of what I am trying to do.

I would like to log the output of the command/program that exec is running.

I have tried to do this using the >> redirection method as follows:

$COMMANDLOG is a parameter to turn command logging off or on.
$LOGNAME is the filename of the file to log to


    if ($COMMANDLOG eq "yes"){
      my $LOGTEXT=sprintf("\$%s\n",$cmd);
      log_list($LOGTEXT);
      $cmd=sprintf("%s >> %s",$cmd,$LOGNAME);
    }
    exec($cmd) or die "exec: $!";
[download]

What happens is that there are two processes running from the exec line and the kill will only kill of the parent of the two processes.

If command logging is turned off, then there is only one process from the exec line.

Please could yoe let me know what the best thing to do about this is.

Thank you.

Richard Thomas.

What happens is that there are two processes running from the exec line and the kill will only kill of the parent of the two processes.

I don't know why a redirection would create 2 processes, but if I wanted to get the output of the child, I would just spawn a child with a filehandle attached, and read it from the parent. I would change the spawn function as follows. WARNING: I haven't tested this at all):

sub spawn
{
    my ($timeout, @cmd) = @_;

    defined( my $child_pid = open(CHILD_OUTPUT, "-|" )
        or die "fork: $!";

    if ($child_pid)
    {
        # parent
        eval
        {
            local $SIG{ALRM} = sub { timeout($child_pid); };
            alarm $timeout;
            while (<CHILD_OUTPUT>)
            {
                # log it
            }
            close(CHILD_OUTPUT) or warn "process $child_pid exited: $?
+";
            alarm 0;
        };

        if ($@)
        {
            print "oops: $@";
        }
    }
    else
    {
        # child
        exec @cmd or die "exec: $!";
    }
}
[download]

--
edan (formerly known as 3dan)