Can you use a scaler as an operator?

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" }
[download]

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.
[download]

Comment on Can you use a scaler as an operator? Select or Download Code

Replies are listed 'Best First'.
Re: Can you use a scaler as an operator? by hippo (Archbishop) 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.	[reply] [d/l]
Re^2: Can you use a scaler as an operator? by AnomalousMonk (Archbishop) on Jan 23, 2014 at 00:12 UTC
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.	[reply] [d/l] [select]
Re^2: Can you use a scaler as an operator? by jar00n (Novice) on Jan 22, 2014 at 21:28 UTC
Very cool, I haven't stumbled across that syntax yet. Thanks	[reply]
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.	[reply] [d/l]