my $ParseErrorFh; BEGIN { open(my $olderr, '>&', STDERR) or die "Cannot dup STDERR: $!"; close STDERR; open(STDERR, '+>', undef) or die "Cannot open anonymous file: $!"; select STDERR; $| = 1; open($ParseErrorFh, '>&STDERR') or die "Cannot dup anoynomous file: $!"; # 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: $!"; } sub report_error { seek($ParseErrorFh, 0, 0); die join '', grep { $_ !~ m/^\s*$/ } <$ParseErrorFh>; } sub parse { my ($grammar, $str) = @_; seek($ParseErrorFh, 0, 0); # To ensure it's not growing indefinitely, as it is package global. my $p = Parse::RecDescent->new($grammar) or report_error(); seek($ParseErrorFh, 0, 0); return $p->startrule($str) or report_error(); }