Check condition in Perl regex for substitution -

i want substitute particular pattern in file other string. want substitution when particular string not matched in pattern.

my code follows:

use warnings; use strict;  $filename = 'c:\test_folder\file.txt'; $pattern = undef;  $read_handle = undef; $string = undef;  open($read_handle, "<", $filename)         || die "$0: can't open $filename reading: $!";  while ( <$read_handle> ){      $string = $string.$_; }   $pattern = qr/(test_case_name.*?:(.*?)\n.*?priority.*?:(\w\d).*?=cut)/s;  $string =~ s{$pattern}{$1\n\nsub $2\n{\n}\n}g; print $string; 

i have stored whole file in string. have following problem:

if in pattern, $3(3rd back-reference) not equal "p3", substitution should occur. how can achieve this?

some sample data input is:

=head2 gen_001

test_case_name :gen_001
priority :p0
release_introduced :7.4 automated :yes

step_name : step1
step_desc :example desc understanding step_result :example result understanding

=cut

=head2 gen_003

test_case_name :gen_003
priority :p1
release_introduced :7.4 automated :no

step_name : step1
step_desc :example desc understanding second testcase
step_result :example result understanding second testcase

=cut

=head2 gen_004

test_case_name :gen_004
priority :p3
release_introduced :7.4 automated :no

step_name : step1
step_desc :example desc understanding third testcase
step_result :example result understanding third testcase

=cut

you can achieve negative lookahead:

(test_case_name.*?:(.*?)\n.*?priority.*?:(?!p3)(\w\d).*?=cut)                                          ^^^^^^ 

see demo

the lookahead (?!p3) makes sure next 2 characters matched (\w\d) not equal p3.