Regular Expression

Predefined character classes

Special character	Matches a	Same as
\d	digit	[0-9]
\D	non-digit	[^0-9]
\w	alphanumeric (word) character	[a-zA-Z0-9_]
\W	non-word character	[^a-zA-Z0-9_]
\s	whitespace character (space, tab, newline...)	[ \t\n\r\f]
\S	non-whitespace character	[^ \t\n\r\f]

Other special backslashed letters are:

Special character	Meaning
\a	alarm (beep)
\n	newline
\r	carriage return
\t	tab
\f	formfeed
\e	escape

Example

#!/usr/local/bin/perl

print "Please enter date and time, as in \"08-OCT-1997  16:30\"\n";
my $entry = <STDIN>;
chop ($entry);

if ($entry =~ /\d\d-\w\w\w-\d\d\d\d  \d\d:\d\d/) {
   print "good!\n";
} else {
   print "wrong format!\n";
}

# Note: an even better conditional would be:
# if ($entry =~ /[0-3]\d-\w\w\w-\d\d\d\d  [0-2]\d:[0-5]\d/) {   }