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

Due to my own syntax bug, what essentially happened was ... 

cat p.pl; echo ; perl -Dr p.pl

printf "matched: %s\n"
  , ( 'x' =~ undef() ? 'yes' : 'no' )
  ;

Omitting $` $& $' support.

EXECUTING...

Compiling REx ""
Final program:
   1: NOTHING (2)
   2: END (0)
minlen 0
Matching REx "" against "x"
   0 <> <x>                  |  1:NOTHING(2)
   0 <> <x>                  |  2:END(0)
Match successful!
matched: yes
Freeing REx: ""

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Is there a way to turn a *match attempt against an undef variable* to be deadly at run time? (I am well aware of the warning generated when matching against an undef value. By that warning itself I had located the error of my ways.)

Replies are listed 'Best First'.
Re: Turn matching against undef to be deadly
by vsespb (Chaplain) on Sep 26, 2013 at 13:16 UTC 
    use strict;
use warnings;
use Carp;


local $SIG{__WARN__} = sub {
if ($_[0] =~ /Use of uninitialized value in regexp compilation/) {
confess $_[0];
} else {
 warn @_;
}
};

print "x".undef, "\n";

printf "matched: %s\n"
  , ( 'x' =~ undef() ? 'yes' : 'no' )
    ;
__END__
Use of uninitialized value in concatenation (.) or string at 1.pl line
+ 14.
x
Use of uninitialized value in regexp compilation at 1.pl line 16.
 at 1.pl line 7.
        main::__ANON__('Use of uninitialized value in regexp compilati
+on at 1.pl line...') called at 1.pl line 16

    [download]


    pros: it works.

    cons:
    1. I think you should at least unit-test it, because warning format can change in different perl versions.
    2. Dynamic scoped (this can be worked around with %^H, probably)
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[d/l]
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[d/l]

      Thanks, vsespb.

      The likelihood of change in warning and having to match against a string are the reasons why I forgot to mention about WARN signal as soon as I had thought about it before posting.

[reply]
        As another Anonymous Monk pointed above you can use warnings 'FATAIL' for all warnings or only "uninitialized". Lexical scope used. But this will catch other types of "uninitialized" warnings. 
        use strict;
use warnings;
use Carp;
use warnings FATAL => 'uninitialized';
printf "matched: %s\n"
  , ( 'x' =~ undef() ? 'yes' : 'no' )
    ;

print "end\n";

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[reply]
[d/l]

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