Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

I'm a total newbie to Perl scripting so please be gentle. I need to write a script that will launch a command and if said command doesn't finish with 5 seconds the script will out put an error to a file. Any tips that can be given would be greatly appreciated. Thank You

Replies are listed 'Best First'.
Re: Track command time
by JavaFan (Canon) on Oct 03, 2008 at 15:20 UTC
    Typically, you'd use an alarm. 
    local $SIG {ALRM} = sub {die "alarm"};

eval {
    alarm (5); 
    system "sleep 10";
    alarm (0);
};
if ($@ && $@ =~ /^alarm/) {
    say "Command interrupted";
}

    [download]
    See also "perldoc -f alarm" and "man perlipc".
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Re: Track command time
by sflitman (Hermit) on Oct 03, 2008 at 16:57 UTC
    I like this code: 
    sub execshell {       # execute a shell command with timeout
   my ($cmd,$timeout)=@_;
   $timeout||=5;  # seconds
   my ($result,$pid,$time);
   eval {
    local $SIG{ALRM} = sub { die "alarm\n" }; # NB: \n required
        local($/)=undef;
        alarm $timeout;
        $pid=open(CMD,"$cmd 2>&1 |");   # run in a shell 
        if ($pid) {
           $result=<CMD>;
           close CMD;
        } else {
           alarm 0;
        }     
    alarm 0;
    };
    if ($@) {
    die $@ unless $@ eq "alarm\n";   # propagate unexpected errors
        $result='TIMEOUT';
    }
    $result;
}

    [download]
    This will time out after 5 seconds by default, and then return result TIMEOUT which you can test for. Otherwise it returns the output of the shell command, or it dies with a message if the shell command was bad for some reason. HTH! SSF
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      This approach (using open vs system) has the added advantage of allowing for concurrency. If you want to run N commands simultaneously, and report errors on those that timeout, this is easy to do. You can use select on all the open filehandles to catch when they output/complete.
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        No. You can only have one alarm and the sequence of setting/resetting $SIG{ALRM} will certainly lead to race conditions.

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