Turn off warning for undefined value in comparison?

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

I looked at perllexwarn, but I cannot figure out what to tell warnings. I really don't like to write

if ( $foo and $foo ne "bar")
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when really I want just

if ( $foo ne "bar" )
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I mean, if it is undefined, it sure is not equal to "bar". So I'd like to turn off just that warning. I cannot figure out (other then by trial and error, I guess) what category to turn off. So, what do I tell "warnings" to turn off just the "undefined in comparison" check? Thanks.

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Re: Turn off warning for undefined value in comparison? by Limbic~Region (Chancellor) on Mar 03, 2004 at 23:16 UTC
traveler, Check out perldoc perldiag. Remember that by using the warnings pragma instead of the -w command line option that you can toggle settings on a per scope basis. `#!/usr/bin/perl use strict; use warnings; no warnings 'uninitialized'; my $foo; print "cool daddy-o\n" if $foo eq 'bar';` [download] Cheers - L~R	[reply] [d/l]
Re: Turn off warning for undefined value in comparison? by cLive ;-) (Prior) on Mar 04, 2004 at 00:41 UTC
I really don't like to write... Why not? It can help you remember context of a var and whether or not it may be undefined at that point. I would use: `if ( defined $foo and $foo ne "bar")` [download] to remind myself that $foo could be undefined, or, when assigning $foo: `# depending on context my $foo = whatever() \|\| ''; my $foo = whatever() \|\| 0;` [download] provided $foo as an empty string/zero is not going to cause you problems. If $foo could be valid as either in a comparison, you need to go the define route (or turn off warnings - yuck!). .02 cLive ;-)	[reply] [d/l] [select]
Re: Turn off warning for undefined value in comparison? by waswas-fng (Curate) on Mar 03, 2004 at 23:17 UTC
`use strict; use warnings; my $foo = ""; if ( $foo ne "bar" ) { print "lala\n"; }` [download] Why is it undefined in the first place? -Waswas	[reply] [d/l]
Re: Turn off warning for undefined value in comparison? by traveler (Parson) on Mar 03, 2004 at 23:45 UTC
Thanks Limbic. I did not know that there was a list there, too. perllexwarn was the only list for 'use warnings' that I could find. waswas-fng in my case I have a hash of values that comes from XML::Simple. If a given tag does not have a parameter e.g.`<foo>blah</foo>` vs. `<foo bar="x">blah</foo>` the value for `$xml->{bar}` is undefined. --traveler	[reply] [d/l] [select]