I recommend reading this article to know more about usage of substr function in perl. Basically substr function and a typical search and replace mechanism (s///g) can be combined to achieve the goal in a single statement.

Look at the following script which replaces the word “goes” to “moves” in first first 10 characters of a string variable “$str”.

#!/usr/bin/perl

$str="What goes around comes around";

print $str . "\n";
substr($str,0,10) =~ s/goes/moves/g;
print $str . "\n";

Output of the above script is as follows:

[neo@techpulp ~]# perl replsubstr.pl
What goes around comes around
What moves around comes around
[neo@techpulp ~]#

You can play with substr as explained in this article to select various range of characters in the string.