# Ditch:
my $string = "Sat, 05 Jan 2013 04:00:15 GMT";
$string =~ s/\d{2} [A-Z][a-z]{2} \d+ //;
print "Take out and ditch: $string\n";
# Output: Take out and ditch: Sat, 04:00:15 GMT

##</code><code>##

# Keep around:
my $string = "Sat, 05 Jan 2013 04:00:15 GMT";
my ($match) = $string =~ m/(\d{2} [A-Z][a-z]{2} \d+)/;
print "Take out and keep: <$match> found in <$string>\n";
# Output: Take out and keep: <05 Jan 2013> found in <Sat, 05 Jan 2013 04:00:15 GMT>

##</code><code>##

# Ditch:
my $string = "Sat, 05 Jan 2013 04:00:15 GMT";
substr($string, 5, 12, "");
print "Take out and ditch: $string\n";
# Output: Take out and ditch: Sat, 04:00:15 GMT

##</code><code>##

# Keep around:
my $string = "Sat, 05 Jan 2013 04:00:15 GMT";
my $match = substr($string, 5, 11); 
print "Take out and keep: <$match> found in <$string>\n";
# Output: Take out and keep: <05 Jan 2013> found in <Sat, 05 Jan 2013 04:00:15 GMT>