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I think there's no <MYPIPE> if open fails

Yes and no: the first <MYPIPE> does return undef, so the while loop never runs, but you should also be getting a warning "readline() on closed filehandle", indicating that something is wrong. A failed open doesn't have to be fatal, there are plenty of ways to handle the control flow:

if ( open my $fh, ... ) { while (<$fh>) { ... } close $fh; } else { warn "open: $!" } # - or - sub foo { open my $fh, ... or do { warn "open: $!"; return }; while (<$fh>) { ... } close $fh; } # - or - FILE: for my $file (@files) { open my $fh, ... or do { warn "skipping $file: $!"; next FILE }; while (<$fh>) { ... } close $fh; } # - or - use Try::Tiny; try { open my $fh, ... or die $!; while (<$fh>) { ... } close $fh; } catch { warn "error: $_"; }; # same thing, but without the module: eval { open my $fh, ... or die $!; ... ;1 } or do { warn "error: $@"; };

The fourth and fifth examples are different in that they catch any fatal error inside the block, which may or may not be desired.

Update: Added the third example, from this thread.

In reply to Re^3: How to handle an external process from CGI? (updated) by haukex
in thread How to handle an external process from CGI? by emilbarton

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