An excellent question. I was brought up on UNIX machines where you should always check the return code of any program you run. As has already been stated a return value of 0 indicates success, anything other value indicates something went wrong.

On UNIX the value returned by system (and its colleagues) is signal_number+256*exit_value. This means that when we call an external program we should inspect the return and interpret the error if there was one. I have a routine to do that (below).

I tested this out on Windows (running 5.005!) and it works the same there.

In my programs I have a special version of system so when I want to run an external program I do:

    &do_system("perl exit1.pl");
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and I don't have to keep remembering to say:

    system("perl exit1.pl") || die "Failed to run exit1.pl\n";
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Anyway here is my old function for your edification…

# This is Perl4 code, I leave the translation to Perl5 
# to the reader

sub do_system
   {
    local($cmd, $reportpattern) = @_;
    local($ret);

    print "# Do command $cmd\n" if($verbose);
    $ret = system($cmd);

    &interp_ret($cmd, $?, $reportpattern);
    return($ret);
    }

sub interp_ret
   {
    local($cmd,$ret,$reportpattern) = @_;
    local($sig,$val,%sig_names,$sig_name);

    return if(!$ret);
    $sig = ($? & 0xff);
    $val = $? >> 8;
    return if ($reportpattern && ! eval($reportpattern));
    # Not quite portable but gets close enough
    %sig_names = 
         (1 ,"SIGHUP" ,2 ,"SIGINT" ,3 ,"SIGQUIT" ,4 ,"SIGILL" ,5 ,"SIG
+TRAP" ,
          6 ,"SIGIOT" ,7 ,"SIGABRT",8 ,"SIGFPE" ,9 ,"SIGKILL" ,
          10,"SIGBUS" ,11,"SIGSEGV" ,12,"SIGSYS",13,"SIGPIPE",14,"SIGA
+LRM",
          15,"SIGTERM", 16,"SIGURG",17,"SIGSTOP",18,"SIGTSTP",19,"SIGC
+ONT",
          20,"SIGCHLD",21,"SIGTTIN",22,"SIGTTOU",23,"SIGIO",24,"SIGXCP
+U",
          25,"SIGXFSZ",26,"SIGVTALRM",27,"SIGPROF",28,"SIGWINCH",29,"S
+IGLOST",
          30,"SIGUSR1",31,"SIGUSR2",);
    print "\nIn script $0 the command \"$cmd\" seemed to fail\n";
    $sig_name = $sig_names{$sig};
    $sig_name = "Unknown SIG $sig" if(!$sig_name);

    if($sig && $val)
       {
        print "Signal $sig_name caused return $val\n";
        }
      elsif($sig)
       {
        print "Signal $sig_name\n";
        }
      else
       {
        print " Returned status $val\n";
        }
    }
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