Increment variables in files - perl

Question

I am a complete rookie with Perl. What I am trying to do is to open a list of files, increment three different variables in each file, save the files, and close.
The variables look like this
This_Is_My_Variable03
This_Is_My_Variable02
This_Is_My_Variable01
The variable ending in 01 is in the file multiple times. The variables are at times part of a Character string. the This_Is_My_Variable part of the variable never changes.
Thanks.
This may not be the best solution but it works
#!perl=C:\IBM\RationalSDLC\ClearCase\bin\perl
use warnings;
use strict;
use Tie::File;
tie my #data, 'Tie::File', 'myfile.txt' or die $!;
s/(This_Is_My_Variable)(\d+)+/$1.++($_=$2)/eg for #data;
untie #data;
Thank you Borodin for getting me started with Tie::File: that definitely helped.
Second solution using while loop
#!perl=C:\IBM\RationalSDLC\ClearCase\bin\perl
use warnings;
#use strict;
sub inc {
my ($num) = #_;
++$num;
}
open(FILE, "myfile.txt") || die $!;
$i = 0;
while (<FILE>) {
$string = $_;
if (/This_Is_My_Variable../) {
$string =~ s/(This_Is_My_Variable)(\d+)+/$1.++($_=$2)/eg;
print "$string \n";
$i++;
}
else {
print "$string \n";
}
}
close FILE;

Answer 1

Your "Second solution using while loop" has a number of problems.
Never disable use strict to get a program working. All that does is hide problems in your code
You have an unused subroutine inc and an unused variable $i
You should always use the three-parameter form of open, and lexical file handles
There is no need to test whether the line contains a string before applying a substitution
You can simply use ($2+1) in your replacement string, rather than assigning the value to $_ and incrementing it with ++($_=$2)
If you are going to use a named variable for the lines read from the file, then generally you should use while (my $string = <$fh>) {...}. For short blocks like this it is better just to use $_
You don't chomp the input, which would be fine except you are printing an additional space and newline after each line
You have print "$string \n" in your code twice. It may as well appear just once outside the if structure
This code performs the same process. I hope it helps.
use strict;
use warnings;
open(my $fh, '<', 'myfile.txt') || die $!;
while (<$fh>) {
s/(This_Is_My_Variable)(\d+)/$1.($2+1)/eg;
print;
}

Answer 2

use strict;
use warnings;
use Tie::File;
tie my #data, 'Tie::File', 'myfile' or die $!;
s/(\d+)$/sprintf '%02d', $1+1/e for #data;