Making same change on many routers

Suppose you need to make the same change on many routers, but do not have fancy software like Cisco Works to help you. No worries. Perl is the best friend of any network and system administrator. Here is the quick script that goes to a router and types command "logging source-interface loopback 0", saves configuration and exit. It can be used to run any command.
Place IP addresses of the routers, one per line, in file routers.txt. This file must be in the same directory as the script. Remember, you put your username, password and enable password in the script in clear text, so do not forget "chmod 700 "

#!/usr/bin/perl
use Net::Telnet::Cisco;
my $myfile="./routers.txt";
open (FH, $myfile) || die "Can not open $myfile\n";

while () {
chomp;
my $switchname=$_;
print "$switchname\n"; 

my $session = Net::Telnet::Cisco->new(Host => $switchname,Input_log => "$switchname.log"); 

# Replace username and password below with real username and password 

$session->login('username', 'password');

# Enable mode
if ($session->enable("enable password") ) { # insert your enable passowrd
    @output = $session->cmd('configure terminal');
    @output = $session->cmd('logging source-interface loopback 0');
    print @output;
    @output = $session->cmd('exit');
    @output = $session->cmd("copy run startup-config\n\n");
    print @output;
    } else {
         warn "Can't enable: " . $session->errmsg;
        }
$session->close;
}
 

Use at your own risk.