# Perl Programming/Regular expressions reference
### Regular expressions with Perl examples

| Metacharacter | 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. | $string1 = "Hello World\n"; if ($string1 =~ m/el*o/) { print "There is an '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 one"; print "and at most two 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 any character not in the square brackets. | $string = "Sky."; if (String =~ /[^aeiou]/) { print "$string doesn't contain any vowels"; } |
| | | 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/ello?\b/) { print "There is a word that ends with"; print " 'ello'\n"; } else { print "There are no words that end with"; print "'ello'\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 '<tt>99 bottles of beer on the wall.</tt>' |
| \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 digit.\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"; } |