http://www.perlmonks.org?node_id=1071577

jar00n has asked for the wisdom of the Perl Monks concerning the following question:

Working on a new script and was hoping to set a variable named $icase and attempt to match a string with this variable used as the operator. So if $icase is defined then it will be equal to 'i' otherwise it'll be undef. With that in mind, is that even logical/efficient/doable? Quick demo to show what I'm seeing: 
#!/usr/bin/perl

$icase = 'i';
$str = 'ASdf';

if ( 'asdf' =~ /$str/$icase ) { print "it works!\n" }

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Which when ran produces this: 
$ perl test.pl
Scalar found where operator expected at test.pl line 6, near "/$str/$i
+case"
        (Missing operator before $icase?)
syntax error at test.pl line 6, near "/$str/$icase "
Execution of test.pl aborted due to compilation errors.

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Replies are listed 'Best First'.
Re: Can you use a scaler as an operator?
by hippo (Bishop) on Jan 22, 2014 at 10:04 UTC

    You would need to use Extended Patterns to accomplish this I think. eg.

    if ( 'asdf' =~ /(?$icase)$str/ ) { print "it works!\n" }

    See the perlre document for full details.

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[d/l]

      Rather than using a defined vs undefined value for the op variable, here's an example of that approach using  'i' vs either  '#' or  '' (empty string). 

      >perl -wMstrict -le
"my $s = 'ASdf';
 ;;
 for my $op ('i', '#', '') {
   printf qq{for op eq '$op': };
   print 'asdf' =~ m{ (?$op) \Q$s\E }xms ? '' : 'NO ', 'match';
   }
"
for op eq 'i': match
for op eq '#': NO match
for op eq '': NO match

      [download]

      Update:  '-i' also works for turning off (or not turning on) case-insensitive matching.

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[d/l]
[select]
      Very cool, I haven't stumbled across that syntax yet. Thanks
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Re: Can you use a scaler as an operator?
by Eily (Monsignor) on Jan 22, 2014 at 10:06 UTC

    I'm afraid this won't work. You can either use an eval, use '/flags' mode, or use the (?adlupimsx-imsx) syntax. Personnaly, I don't like the second solution much, but the two others are mostly the same to me.

    Eventually, if it's just a case matter, and not any flag, you could also lc the input.

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[d/l]

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