Perl Regex match works, but replace does not

I have put together a Perl script to go through a directory and match various keys in the source and output the results to a text file. The match operation works well, however the end goal is to perform a replace operation. The Perl script is as follows:

  #!/usr/bin/perl
  #use strict;
  use warnings;

  #use File::Slurp;

  #declare variables
  my $file = '';
  my $verbose = 0;
  my $logfile;

  my @files = grep {/[.](pas|cmm|ptd|pro)$/i} glob 'C:\users\perry_m\desktop\epic_test\pascal_code\*.*';

  #iterate through the files in input directory
  foreach $file (@files) {

     print "$file\n";

     #read the file into a single string
     open FILEHANDLE, $file or die $!;
     my $string = do { local $/; <FILEHANDLE> };

     #perfrom REGEX on this string

     ########################################################
     #fix the include formats to conform to normal PASCAL
     $count = 0;
     while ($string =~ m/%INCLUDE/g)
     {
        #%include
        $count++;
     }
     if ($count > 0)
     {
        print " $count %INCLUDE\n";
     }
     $count = 0;
     while ($string =~ m/INCLUDE/g)
     {
        #%INCLUDE;
        $count++;
     }
     if ($count > 0)
     {
        print " $count INCLUDE\n";
     }
     $count = 0;
     while ($string =~ m/(%include\s+')[A-Za-z0-9]+:([A-Za-z0-9]+.[A-Za-z]+')/g)
     {
        #$1$2;
        $count++;
     }
     if ($count > 0)
     {
        print " $count XXXX:include \n";
     }        
  }

This produces output as desired, an example is below:

  C:\users\perry_m\desktop\epic_test\pascal_code\BRTINIT.PAS
   1 INCLUDE
   2 XXXX:include 
   39 external and readonly

However if I change the regex operations to try and implement a replace, using the replacement operation shown in the commented lines above, the scripts hangs and never returns. I imagine it is somehow related to memory, but I am new to Perl. I was also trying to avoid parsing the file by line if possible.

Example:

  while ($string =~ s/%INCLUDE/%include/g)
  {
     #%include
     $count++;
  }

and

  while ($string =~ s/(%include\s+')[A-Za-z0-9]+:([A-Za-z0-9]+.[A-Za-z]+')/$1$2;/g)
  {
     #$1$2;
     $count++;
  }

Edit: simplified the examples