Here are some examples of Perl regular expressions.
| 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, ... later to refer to the previously matched pattern. |
$string1 = "Hello World\n";
if ($string1 =~ m/(H..).(o..)/) {
print "We matched '$1' and '$2'\n";
}
<B>Output:</B>
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";
}
|
| ? | Modifies the *, +, or {M,N}'d regexp that comes before to match as few times as possible. |
$string1 = "Hello World\n";
if ($string1 =~ m/(l.+?o)/) {
print "The non-greedy match with 'l' followed by one or ";
print "more characters is 'llo' rather than 'llo wo'.\n";
}
|
| * | Matches zero or more times. |
$string1 = "Hello World\n";
if ($string =~ 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 1";
print "and at most 2 l's in $string1\n";
}
|
| [...] | Denotes a set of possible character matches. |
$string1 = "Hello World\n";
if ($string1 =~ m/[aeiou]+/) {
print "$string1 contains one or more vowels.\n";
}
|
| | | Separates alternate possibilities. |
$string1 = "Hello World\n";
if ($string1 =~ m/(Hello|Hi|Pogo)/) {
print "At least one of Hello, Hi, or Pogo is ";
print "contained in $string1.\n";
}
|
| \b | Matches a word boundary. |
$string1 = "Hello World\n";
if ($string1 =~ m/llo\b/) {
print "There is a word that ends with 'llo'\n";
} else {
print "There are no words that end with 'llo'\n";
}
|
| \w | Matches alphanumeric, including "_". |
$string1 = "Hello World\n";
if ($string1 =~ m/\w/) {
print "There is at least one alphanumeric ";
print "character 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, form feed) |
$string1 = "Hello World\n";
if ($string1 =~ m/\s.*\s/) {
print "There are TWO whitespace characters, which may";
print " be 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 characters, which";
print " may be 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";
}
<B>Output:</B>
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 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";
}
|
| \A | Matches the beginning of a string (but not an internal line). |
$string1 = "Hello\nWorld\n";
if ($string1 =~ m/\AH/) {
print "$string1 is a string";
print "that starts with 'H'\n";
}
|
| \Z | Matches the end of a string (but not an internal line). |
$string1 = "Hello\nWorld\n";
if ($string1 =~ m/d\n\Z/) {
print "$string1 is a string";
print "that ends with 'd\\n'\n";
}
|
| [^...] | Matches every character except the ones inside brackets. |
$string1 = "Hello World\n";
if ($string1 =~ m/[^abc]/) {
print "$string1 does not contain the characters ";
print "a, b, and c\n";
}
|
The 'm' in the above regular expressions, for example m/[^abc]/, is not required in order for perl to recognize the expression as a 'match' (cf. 'substitute': s/a/b/); /[^abc]/ could just as easily be used without the preceding 'm'. The 'm' operator can be used to alter the delimiting character; for example, m{/} may be used to enhance the legibility of patterns such as /\//. See 'perldoc perlre' for more details.