Re^3: Capturing errors from 3-arg pipe open in ActivePerl 5.020

The problem is that if I fat-finger the open command (e.g. type "-zom" instead "-zoom" in the command arguments)

You ought to detect that kind of error the first time you test your script; so correct the typo.
or if "$PDF_FILE" could not be found, the program merrily continues on its way, unaware that $XML is undefined.

This kind of depends on what the executable does in that situation. I'll assume it does the sensible thing of outputting an error message then exits with a non zero exit code.
Normally, if you were reading the pipe yourself, the first time you attempted to read it would get a end of file (with a pipe abandoned status) and you could then call waitpid on the pid returned by the open, and check $? to obtain the exit code and status.
As you are passing the filehandle into a module, the simplest check would be to call eof on the filehandle before you give it to XML::Twig; and if there's nothing to read, don't pass it on; just waitpid and check $?

It can get more complicate if the executable is one of those that tries to be 'helpful' and hangs around rather than just exiting on error; but let's assume it's not :)

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority". I knew I was on the right track :)

In the absence of evidence, opinion is indistinguishable from prejudice.

Comment on Re^3: Capturing errors from 3-arg pipe open in ActivePerl 5.020 Select or Download Code

Replies are listed 'Best First'.
Re^4: Capturing errors from 3-arg pipe open in ActivePerl 5.020 by ateague (Monk) on Nov 16, 2015 at 21:03 UTC
As you are passing the filehandle into a module, the simplest check would be to call eof on the filehandle before you give it to XML::Twig; That certainly did the trick, thank you very much! pipe.pl `#!/usr/bin/perl use 5.020; use strict; use warnings; open (my $ARTICLE, "-\|", "caesar"); eof $ARTICLE and die "Can't start caesar:\n$!\n$^E"; my $read = <$ARTICLE>; say "[$read]";` [download] Results: `perl pipe.pl 'caesar' is not recognized as an internal or external command, operable program or batch file. Can't start caesar: Inappropriate I/O control operation The handle is invalid at pipe.pl line 7.` [download]	[reply] [d/l] [select]

Replies are listed 'Best First'.

Re^4: Capturing errors from 3-arg pipe open in ActivePerl 5.020
by ateague (Monk) on Nov 16, 2015 at 21:03 UTC

As you are passing the filehandle into a module, the simplest check would be to call eof on the filehandle before you give it to XML::Twig;

That certainly did the trick, thank you very much!

pipe.pl

#!/usr/bin/perl
use 5.020;
use strict;
use warnings;

open (my $ARTICLE, "-|", "caesar");
eof $ARTICLE and die "Can't start caesar:\n$!\n$^E";

my $read = <$ARTICLE>;
say "[$read]";
[download]

Results:

perl pipe.pl
'caesar' is not recognized as an internal or external command,
operable program or batch file.
Can't start caesar:
Inappropriate I/O control operation
The handle is invalid at pipe.pl line 7.
[download]

[reply]
[d/l]
[select]