"I can't find any tutorials that actually teach you how to do it with a text input!"

Did you look in the tutorials section of this site? If you had done you would have found Perl Babysteps 1: Your First Simple Script. When posting here please post error messages, saying things "obviously" don't work is not ideal. Check out How do I post a question effectively? and the PerlMonks FAQ if you have not already done so.

It looks to me that you could benefit from reading some documentation (see comments in code below) and some basic tutorials

#!usr/bin/perl

use strict; # perldoc strict
use warnings; # perldoc warnings

print "type hw to print hello world script!\n:> ";

my $cmd = <STDIN>;

chomp($cmd); # perldoc -f chomp

if ( $cmd eq "hw" ){ # does $cmd contain hw?
    print "Hello, world";
}else{
    print "sorry I didn't understand the command.";
}
[download]

Hope this helps

Update: changed stdin to STDIN thanks to Corion's keen eye :)

Martin