perlquestion w-ber <p> Dear monks, </p> <p> I would like to capture the error output of [cpan://Parse::RecDescent] to a variable instead of printing it to <code>STDERR</code>. There does not seem to be any way of doing this easily; there is no documentation for it, and viewing the source code reveals that </p> <ol> <li>the module dups <code>STDERR</code> into its own filehandle called <code>ERROR</code>, and</li> <li>the module defines a format called <code>ERROR</code> for printing to the filehandle.</li> </ol> <p> Since the <code>ERROR</code> filehandle is defined at module <code>use</code> time, it is necessary to do <code>STDERR</code> munging in a <code>BEGIN</code> block, thusly: </p> <code> my $ParseError; BEGIN { open(my $olderr, '>&', STDERR) or die "Cannot dup STDERR: $!"; close STDERR; open(STDERR, '>', \$ParseError) or die "Cannot open in-memory file: $!"; select STDERR; $| = 1; # Cannot use, since that messes up execution order for some reason (since use # implies a BEGIN block itself?). require Parse::RecDescent; close STDERR; open(STDERR, '>&', $olderr) or die "Cannot restore STDERR: $!"; } # Then later: my $p = Parse::RecDescent->new($grammar) or die "Invalid grammar"; my $output = $p->startrule($str) or die $ParseError; </code> <p> However, fine as it is though hairy, this will not produce any content in <code>$ParseError</code>, which will stay undefined. If I replace the <code>STDERR</code> re-open with an opening of a file, say </p> <code> open(STDERR, '>', '/tmp/error') or die $!; </code> <p> I do get the error strings in <code>/tmp/error</code>! </p> <p> Is the cause of the problem the use of <code>format</code> in <code>Parse::RecDescent</code>, or some other subtle things I'm missing? An issue with buffering? Or is the approach fundamentally flawed? I guess I could open an anonymous temporary file somehow, redirect <code>STDERR</code> to that, then read in the contents of the file, but surely there is a better way. (This is on Perl 5.8.8 on Linux, x86_64, if that's relevant.) </p> <div class="pmsig"> <div class="pmsig-399589"> <p> -- <br> print "Just Another [href://http://prometheus.frii.com/~gnat/yapc/2000-stages/slide25.html|Perl Adept]\n"; </p> </div> </div>