perlquestion
pjf
<p>
Wise monks,
</p><p>
I've been spending my time recently working upon a new revision of <a href="http://search.cpan.org/perldoc?IPC::System::Simple">IPC::System::Simple</a>, a module designed to take the headache out of calling external commands. Unfortunately, I've hit a snag under Windows.
</p><p>
My Windows system (WinXP, ActivePerl 5.8.8) appears to assign a value of <tt>1 << 8</tt> to <tt>$?</tt> upon failure to start a process. The following example demonstrates this:
</p>
<code>
system("this_command_does_not_exist",1);
printf("raw: %d ; apparent exit: %d\n",$?, $?>>8);
</code>
<p>
Unfortunately, this is indistinguishable from the command running to completion and returning an exit status of 1. Not being able to tell the difference is a <i>very bad thing</i>. There's also a troublesome error message that is printed (<i>'...' is not recognised as an internal or external command</i>) that I assume is from the Windows shell, and ideally I'd love to supress the printing of this message.
</p><p>
Using the multiple argument version of system does not alter these results.
</p><p>
I'm sure there must be a way under Windows to tell if a command did not start, and it's probably something simple, but I'm at a loss to find it.
</p><p>
Any tips and pointers would be greatly appreciated.
</p><p>
<b>Update:</b> This problem isn't exactly unique to Windows. When using single-argument <tt>system()</tt> under Unix with shell meta-characters, the result in <tt>$?</tt> reflects the exit value of the shell, which returns 127 on a failure to find the command. This is indistinguishable from a successfully executed command returning an exitval of 127.
</p>
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<div class="pmsig"><div class="pmsig-116014">
<i>Paul Fenwick</i><br>
<a href="http://perltraining.com.au/">Perl Training Australia</a>
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