There's no need to change directories, though you can do it with the chdir command.

Here's some code that will do what you want:

#!/usr/bin/perl
use warnings;
use strict;

#
# Open file for reading (explicit), die on error
#
open SERVICES, '<', '/etc/services'
    or die "cannot open /etc/services: $!";

#
# Read thru each line (put into $_), and print the captured
# comment text if the line has a comment (anything after a #
# to the end of line).  Note that this doesn't include the 
# hash (pound, octothorpe, et al.); move it inside the parens
# for that behavior.
#
while (<SERVICES>) { print "$1\n" if /#(.*)$/ }

# Close filehandle
close SERVICES;
[download]

Update Note in comment about not printing the hash mark.

use strict;
use warnings;
use IO::File;

my $f = new IO::File "/etc/services", "r"
    or die "can not read services file";

while (<$f>) {
    print "$1\n" if /(#.*)$/;
}
[download]

grep \# /etc/services | cut -f2 -d#
[download]

While technically correct, I'd argue that there is no reason to bring IO::File into this (especially for the OP, who obviously doesn't need to mess with that module now). Perl's open will work just fine; why use a module when you don't need to?

Well, IO::File is my preferred way for file I/O, I always use it unintentionally. I agree the OP is probably a bit green on Perl, but it shouldn't hurt to show him another way of openning files, should it. ;-)