Perl Regex match works, but replace does not - regex

Question

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

Answer 1

The problem is with your while loops. A loop like
while ($string =~ m/INCLUDE/g) { ... }
will execute once for each ocurrence of INCLUDE in the target string, but a subtitution like
$string =~ s/INCLUDE/%INCLUDE;/
will make all of the replacement in one go and retuen the number of replacements made. So a loop
while ($string =~ s/INCLUDE/%INCLUDE;/g) { ... }
will endlessly add more and more percentage signs before and semicolons after every INCLUDE.
To find the number of replacements made, change all your loops like this to just
$count = $string =~ s/INCLUDE/%INCLUDE;/g

Answer 2

the pattern in s/INCLUDE/%INCLUDE/g will match the replacement also, so if you're running it in a while loop it will run forever (until you run out of memory).
s///g will replace all matches in a single shot so you very rarely will need to put it in a loop. Same goes for m//g, it will do the counting in a single step if you put it in list context.