UTF8

# flags source code as UTF8
use utf8;

# flags STDOUT as UTF8
binmode(STDOUT, ":encoding(utf-8)");

Stop "sshd" in Ubuntu

Internet says this one works: 
sudo update-rc.d -f sshd remove

but  it isn't.
It does NOT work.
The following works: 
sudo apt-get remove openssh-server

Real UID vs Effective UID

If you think about a large company where employees have different levels of access to different locations, you could compare the Real User ID to the name badges people wear, and the Effective User ID to the set of keys they've been given.

Perl module version

perl -MDateTime -le 'print DateTime->VERSION'

OR:

pmvers DateTime

Perl - read in a whole file at once

use Perl6::Slurp;
my $data = slurp 'path/to/file';

OR

use File::Slurp;
my $text = read_file( 'filename' );
my $lines = read_file( 'filename', array_ref => 1 );
my $lines = read_file( 'filename', array_ref => 1, chomp => 1 );

OR

use File::Slurper;

OR

my $body = do { local( @ARGV, $/ ) = $filename; <> };

OR (if the file is under __DATA__)

my $body = join( '', <DATA> );

Permissions

(not optimised for performance, but does the job):

find . -name '.svn' -prune -o -type d -exec chown www-data:www-data {} \;
-exec chmod 700 {} \; -o -type f -exec chown www-data:www-data {} \; -exec chmod 600 {} \;

List all users

List all users:
awk -F: '{ print $1 }' /etc/passwd

List all members of a group:
awk -F: '/^groupname/ {print $4;}' /etc/group