You should read up on index, length and substr:

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

# Example strings
my $string1 = "ABCDEFderp12345";
my $string2 = "derp";

# Find position of string2 within string1
my $strpos = index($string1, $string2);

# If $strpos is greater than zero (see perldoc index)
if ( $strpos >= 0 ){

    # Print remainder of the string
    # See perldoc length, perldoc substr
    print substr( $string1, ( $strpos + length($string2) ) );
}else{
    print "$string2 does not occur within $string1";
}
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In the above basic example above we find out if $string2 exists within $string1. If $string2 does not exist within $string1 then index will return -1, otherwise it'll return the position where $string2 occurs. substr can be used to get the text from $string1 after $string2, but we need to add the length of $string2 to the position returned by index as it's offset, because you don't want to include $string2 in what gets printed.

Further recommended reading:

• perlintro
• http://learn.perl.org
• http://perldoc.perl.org
• The tutorials section of this site, including PerlMonks for the Absolute Beginner

Update: changed gt 0 to >= 0. I wasn't quite awake when I posted. Thanks AnomalousMonk for pointing this out.

Update 2: Slight rewording for clarity.