Perl

Regular Expression	Description	Example Note that all the if statements return a TRUE value
.	Matches an arbitrary character, but not a newline.	$string1 = "Hello World\\n"; if ($string1 =~ m/...../) { print "$string1 has length >= 5\\n"; }
( )	Groups a series of pattern elements to a single element. When you match a pattern within parentheses, you can use any of $1, $2, ... $9 later to refer to the previously matched pattern.	Program: $string1 = "Hello World\\n"; if ($string1 =~ m/(H..).(o..)/) { print "We matched '$1' and '$2'\\n"; } Output: We matched 'Hel' and 'o W';
+	Matches the preceding pattern element one or more times.	$string1 = "Hello World\\n"; if ($string1 =~ m/l+/) { print "There are one or more consecutive l's in $string1\\n"; }
?	Matches zero or one times.	$string1 = "Hello World\\n"; if ($string1 =~ m/H.?e/) { print "There is an 'H' and a 'e' separated by "; print "0-1 characters (Ex: He Hoe)\\n"; }
?	Matches the *, +, or {M,N}'d regexp that comes before as few times as possible.	$string1 = "Hello World\\n"; if ($string1 =~ m/(l+?o)/) { print "The non-greedy match with one or more 'l' print "followed by an 'o' is 'lo', not 'llo'.\\n"; }
*	Matches zero or more times.	$string1 = "Hello World\\n"; if ($string =~ m/el*o/) { print "There is a 'e' followed by zero to many"; print "'l' followed by 'o' (eo, elo, ello, elllo)\\n"; }
{M,N}	Denotes the minimum M and the maximum N match count.	$string1 = "Hello World\\n"; if ($string1 =~ m/l{1,2}/) { print "There exists a substring with at least 1"; print "and at most 2 l's in $string1\\n"; }
[...]	Denotes a set of possible matches.	$string1 = "Hello World\\n"; if ($string1 =~ m/[aeiou]+/) { print "$string1 contains a one or more"; print "vowels\\n"; }
|	Matches one of the left or right operand.	$string1 = "Hello World\\n"; if ($string1 =~ m/(Hello|Hi)/) { print "Hello or Hi is "; print "contained in $string1"; }
\\b	Matches a word boundary.	$string1 = "Hello World\\n"; if ($string1 =~ m/\\bllo\\b/) { print "There is a word that starts with"; print " 'llo'\\n"; } else { print "There are no words that start with"; print "'llo'\\n"; }
\\w	Matches alphanumeric, including "_".	$string1 = "Hello World\\n"; if ($string1 =~ m/\\w/) { print "There is at least one alpha-"; print "numeric char in $string1 (A-Z, a-z, 0-9, _)\\n"; }
\\W	Matches a non-alphanumeric character.	$string1 = "Hello World\\n"; if ($string1 =~ m/\\W/) { print "The space between Hello and "; print "World is not alphanumeric\\n"; }
\\s	Matches a whitespace character (space, tab, newline, formfeed)	$string1 = "Hello World\\n"; if ($string1 =~ m/\\s.*\\s/) { print "There are TWO whitespace "; print "characters separated by other characters in $string1"; }
\\S	Matches anything BUT a whitespace.	$string1 = "Hello World\\n"; if ($string1 =~ m/\\S.*\\S/) { print "There are TWO non-whitespace "; print "characters separated by other characters in $string1"; }
\\d	Matches a digit, same as [0-9].	$string1 = "99 bottles of beer on the wall."; if ($string1 =~ m/(\\d+)/) { print "$1 is the first number in '$string1'\\n"; } Output: 99 is the first number in '99 bottles of beer on the wall.'
\\D	Matches a non-digit.	$string1 = "Hello World\\n"; if ($string1 =~ m/\\D/) { print "There is at least one character in $string1"; print "that is not a string.\\n"; }
^	Matches the beginning of a line or string.	$string1 = "Hello World\\n"; if ($string1 =~ m/^He/) { print "$string1 starts with the characters 'He'\\n"; }
$	Matches the end of a line or string.	$string1 = "Hello World\\n"; if ($string1 =~ m/rld$/) { print "$string1 is a line or string"; print "that ends with 'rld'\\n"; }