checking bareword-filehandle

morgon has asked for the wisdom of the Perl Monks concerning the following question:

I have inherited some tangled mess of code that uses barewords for filehandles like so:

open FH, ">whatever" or warn "blah";
# much much later
print FH "something";
[download]

The problem is that when the open fails the code goes on (doing many other things) and when it comes to the print Perl emits a warning as FH is not an open filehandle (strict and warnings are on).

I don't want to go into the code right now, all I want is to suppress the warning, but I cannot write

if(FH) { print FH "something" }
[download]

as FH is a bareword.

So my question is: What is the idiomatic way to check a such a filehandle?

Many thanks!

Comment on checking bareword-filehandle Select or Download Code

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Re: checking bareword-filehandle by BrowserUk (Patriarch) on Aug 06, 2012 at 14:04 UTC
`if( fileno(FH) ) { print FH "something" }` [download] 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". In the absence of evidence, opinion is indistinguishable from prejudice. The start of some sanity?	[reply] [d/l]
Re: checking bareword-filehandle by moritz (Cardinal) on Aug 06, 2012 at 13:18 UTC
Is there a good reason not to use a lexical variable as file handle? `open my $FH, '>', 'whatever' or warn 'blah'; # much much later if ($FH) { print $FH "something }` [download] works for sure. Perl 6 - the future is here, just unevenly distributed	[reply] [d/l]
Re^2: checking bareword-filehandle by morgon (Priest) on Aug 06, 2012 at 13:24 UTC
Evidently, but at the moment the open is in a different lexial scope as the print so I would need to declare a lexical $FH in the common enclosing scope - I'll do that eventually. But apart from your suggestions for suppressing the warning outright - is there really no easy way for checking such a handle?	[reply]
Re^3: checking bareword-filehandle by moritz (Cardinal) on Aug 06, 2012 at 13:30 UTC
After skimming perlmod and perlref I've dug up `print FH $foo if *{$foo}{IO};` [download] which is somewhat ugly, but seems to work. Perl 6 - the future is here, just unevenly distributed	[reply] [d/l]
Re: checking bareword-filehandle by johngg (Canon) on Aug 06, 2012 at 13:14 UTC
Wrap the `print` in an eval perhaps? Cheers, JohnGG	[reply] [d/l]
Re^2: checking bareword-filehandle by moritz (Cardinal) on Aug 06, 2012 at 13:20 UTC
eval only traps errors, not warnings. `no warnings 'unopened';` [download] Inside a small block should work though. See perllexwarn. Perl 6 - the future is here, just unevenly distributed	[reply] [d/l]
Re^3: checking bareword-filehandle by morgon (Priest) on Aug 06, 2012 at 14:15 UTC
seems not to work in my old Perl (5.8.8): `use strict; use warnings; no warnings qw(unopened); open HUBBA, "/hubba"; print HUBBA "hubba";` [download] Produces a warning "print() on closed filehandle HUBBA at t line 6." Guess I have to disable all warnings...	[reply] [d/l]
Re^4: checking bareword-filehandle by moritz (Cardinal) on Aug 06, 2012 at 14:20 UTC
Re: checking bareword-filehandle by ww (Archbishop) on Aug 06, 2012 at 13:46 UTC
So change to a lexical filehandle. Or does "I don't want to go into the code right now" mean something other than "I don't have time/inclination/skills to do it right?"	[reply]
Re: checking bareword-filehandle by davido (Cardinal) on Aug 06, 2012 at 16:42 UTC
Checking a filehandle is problematic. Why not change your open to something like this: `open FH, '<', 'filename' or do { $failed = 1; warn $! };` [download] Now you've got a reliable Boolean variable rather than fragile hackish testing of the filehandle. Dave	[reply] [d/l]
Re: checking bareword-filehandle by aitap (Curate) on Aug 06, 2012 at 13:23 UTC
Perhaps, autodie can help you? For example, `use autodie qw(open close);`. Sorry if my advice was wrong.	[reply] [d/l]
Re: checking bareword-filehandle by rovf (Priest) on Aug 06, 2012 at 14:59 UTC
How about changing the open to `use File::Spec::Functions qw(devnull); ... if(!open(FH, ">...")) { warn " ... $!..."; open(FH,'>',devnull) or die "$!"; }` [download] If you can't even write to the bitbucket, something is really messed up in your system, so I think it makes sense to die in that case. -- Ronald Fischer <ynnor@mm.st>	[reply] [d/l]