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

$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"; } }


[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.