Perl Programming/Regular expressions reference
Regular expressions with Perl examples
edit| 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";
}
|