Re^2: Regex error when [] occurs in file..

[why_bird]

Thanks both---I didn't realise that $' was treated like that. Are all 'special variables' ($&, $N (N is integer)) expanded in that way too? So if you did something like:

$temp =~ m/(\[0-9\])blah$1/;

would you match

$temp = "[0-9]blah6";

rather than

$temp = "[0-9]blah[0-9]";

?
V. interesting---I assumed that special characters inside the rest of the data would be ignored..
Cheers
<--edit to make the last sentence make more sense!-->

[Joost]

Are all 'special variables' ($&, $N (N is integer)) expanded in that way too?

All variables are expanded that way, special or not:

my $var = '[ab]';
my $string = '12a3434';
print "match" if $string =~ /$var/;

See also quotemeta and the \Q and \E escape sequences.

[almut]

$temp =~ m/(\[0-9\])blah$1/;

I think you meant

$temp =~ m/(\[0-9\])blah\1/;

in which case any special characters in the content of the backreference \1 would not be treated special. IOW, "[0-9]blah[0-9]" would match, but not "[0-9]blah6":

#!/usr/bin/perl

use strict;
use warnings;

for my $temp ("[0-9]blah[0-9]", "[0-9]blah6") {
    printf "%-15s ", $temp;
    if ($temp =~ /(\[0-9\])blah\1/) {
        print "matched\n";
    } else {
        print "didn't match\n";
    }
}

prints

[0-9]blah[0-9]  matched
[0-9]blah6      didn't match

while, if you replace \1 with $1 in the above regex, it prints

Use of uninitialized value in concatenation (.) or string at ./671663.
+pl line 8.
[0-9]blah[0-9]  matched
[0-9]blah6      matched

This is because $1 isn't defined here, thus the regex effectively becomes /(\[0-9\])blah/...

Update: added demo code.