So you're trying to say that $uname doesn't match as a regular expression?

Doesn't using quotemeta change that?

Maybe you want to add case insensitivity (s///i) ?

See How do I post a question effectively? and write this

#!/usr/bin/perl --
use strict; use warnings;
use Data::Dump qw/ dd /;

my $input = 'servername.EXAMPLE.com  servername';
my $wantedOutput = 'newname.EXAMPLE.com  newname';
my $replacement = 'newname';
my $uname = quotemeta 'servername'; ###

dd $input;

for( $input ){
    s/$uname/$replacement/gi;
}

dd $input;
dd $wantedOutput ;
__END__
"servername.EXAMPLE.com  servername"
"newname.EXAMPLE.com  newname"
"newname.EXAMPLE.com  newname"
[download]

As you can see through my use of Data::Dump::dd, it worked, $input has changed and it now looks like $wantedOutput