HI Corion Please find my code as follow

use strict;
use warnings;

use Path::Tiny qw(path);
my $filenme='d:\SampleCiscoIOSEvent.txt';
my $file=path($filenme);
my $data= $file->slurp_utf8;
use File::Slurp;
my $filename='e:\filename.txt';
my @arr = read_file($filename);
my @output= map{ $data=~s/C_USERNAME/$_/rg} @arr;
print @output;
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