$ cat test4.pl
#!/usr/bin/perl
use strict;
use warnings;

sub noalias {
    my ($arg)=@_;
    $arg = uc($arg);
    print "Arg: $arg.\n";
}

sub alias {
    $_[0] = uc($_[0]);
    print "Arg: $_[0].\n";
}

my $t1 = "foobar";
my $t2 = "barbaz";

noalias($t1);
alias($t2);

print "T1: $t1, T2: $t2.\n";

$ perl test4.pl
Arg: FOOBAR.
Arg: BARBAZ.
T1: foobar, T2: BARBAZ.