Php Regular Expression Cheat Sheet

Posted : admin On 1/3/2022

Welcome to RegExLib.com, the Internet's first Regular Expression Library.Currently we have indexed 25935 expressions from 2982 contributors around the world. We hope you'll find this site useful and come back whenever you need help writing an expression, you're looking for an expression for a particular task, or are ready to contribute new expressions you’ve just figured out. Regular expression tester with syntax highlighting, explanation, cheat sheet for PHP/PCRE, Python, GO, JavaScript, Java. Features a regex quiz & library.

Test PHP regular expressions live in your browser and generate sample code for pregmatch, pregmatchall, pregreplace, preggrep, and pregsplit! — A Live Regular Expression Tester for PHP. Cheat Sheet abc A single character of: a, b or c ^abc Any single character except: a, b, or c a-z. Using Regular Expression, searching a pattern in the text becomes easy. The search done with regular expression is called potential search. Regular Expression is represented in-between 2 forward slash ( '/' ) character. Table of Contents. Literal Pattern. Literal pattern is.

The tables below are a reference to basic regex. While reading the rest of the site, when in doubt, you can always come back and look here. (It you want a bookmark, here's a direct link to the regex reference tables). I encourage you to print the tables so you have a cheat sheet on your desk for quick reference.
The tables are not exhaustive, for two reasons. First, every regex flavor is different, and I didn't want to crowd the page with overly exotic syntax. For a full reference to the particular regex flavors you'll be using, it's always best to go straight to the source. In fact, for some regex engines (such as Perl, PCRE, Java and .NET) you may want to check once a year, as their creators often introduce new features.
The other reason the tables are not exhaustive is that I wanted them to serve as a quick introduction to regex. If you are a complete beginner, you should get a firm grasp of basic regex syntax just by reading the examples in the tables. I tried to introduce features in a logical order and to keep out oddities that I've never seen in actual use, such as the 'bell character'. With these tables as a jumping board, you will be able to advance to mastery by exploring the other pages on the site.

How to use the tables

The tables are meant to serve as an accelerated regex course, and they are meant to be read slowly, one line at a time. On each line, in the leftmost column, you will find a new element of regex syntax. The next column, 'Legend', explains what the element means (or encodes) in the regex syntax. The next two columns work hand in hand: the 'Example' column gives a valid regular expression that uses the element, and the 'Sample Match' column presents a text string that could be matched by the regular expression.
You can read the tables online, of course, but if you suffer from even the mildest case of online-ADD (attention deficit disorder), like most of us… Well then, I highly recommend you print them out. You'll be able to study them slowly, and to use them as a cheat sheet later, when you are reading the rest of the site or experimenting with your own regular expressions.
Enjoy!
If you overdose, make sure not to miss the next page, which comes back down to Earth and talks about some really cool stuff: The 1001 ways to use Regex.

Regex Accelerated Course and Cheat Sheet

For easy navigation, here are some jumping points to various sections of the page:
✽ Characters
✽ Quantifiers
✽ More Characters
✽ Logic
✽ More White-Space
✽ More Quantifiers
✽ Character Classes
✽ Anchors and Boundaries
✽ POSIX Classes
✽ Inline Modifiers
✽ Lookarounds
✽ Character Class Operations
✽ Other Syntax
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Characters

CharacterLegendExampleSample Match
dMost engines: one digit
from 0 to 9
file_ddfile_25
d.NET, Python 3: one Unicode digit in any scriptfile_ddfile_9੩
wMost engines: 'word character': ASCII letter, digit or underscorew-wwwA-b_1
w.Python 3: 'word character': Unicode letter, ideogram, digit, or underscorew-www字-ま_۳
w.NET: 'word character': Unicode letter, ideogram, digit, or connectorw-www字-ま‿۳
sMost engines: 'whitespace character': space, tab, newline, carriage return, vertical tabasbsca b
c
s.NET, Python 3, JavaScript: 'whitespace character': any Unicode separatorasbsca b
c
DOne character that is not a digit as defined by your engine's dDDDABC
WOne character that is not a word character as defined by your engine's wWWWWW*-+=)
SOne character that is not a whitespace character as defined by your engine's sSSSSYoyo

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Quantifiers

QuantifierLegendExampleSample Match
+One or moreVersion w-w+Version A-b1_1
{3}Exactly three timesD{3}ABC
{2,4}Two to four timesd{2,4}156
{3,}Three or more timesw{3,}regex_tutorial
*Zero or more timesA*B*C*AAACC
?Once or noneplurals?plural

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More Characters

CharacterLegendExampleSample Match
.Any character except line breaka.cabc
.Any character except line break.*whatever, man.
.A period (special character: needs to be escaped by a )a.ca.c
Escapes a special character.*+? $^/.*+? $^/
Escapes a special character[{()}][{()}]

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Logic

LogicLegendExampleSample Match
Alternation / OR operand22 3333
( … )Capturing groupA(nt pple)Apple (captures 'pple')
1Contents of Group 1r(w)g1xregex
2Contents of Group 2(dd)+(dd)=2+112+65=65+12
(?: … )Non-capturing groupA(?:nt pple)Apple

(direct link)Php Regular Expression Cheat Sheet

More White-Space

CharacterLegendExampleSample Match
tTabTtw{2}T ab
rCarriage return charactersee below
nLine feed charactersee below
rnLine separator on WindowsABrnCDAB
CD
NPerl, PCRE (C, PHP, R…): one character that is not a line breakN+ABC
hPerl, PCRE (C, PHP, R…), Java: one horizontal whitespace character: tab or Unicode space separator
HOne character that is not a horizontal whitespace
v.NET, JavaScript, Python, Ruby: vertical tab
vPerl, PCRE (C, PHP, R…), Java: one vertical whitespace character: line feed, carriage return, vertical tab, form feed, paragraph or line separator
VPerl, PCRE (C, PHP, R…), Java: any character that is not a vertical whitespace
RPerl, PCRE (C, PHP, R…), Java: one line break (carriage return + line feed pair, and all the characters matched by v)

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More Quantifiers

QuantifierLegendExampleSample Match
+The + (one or more) is 'greedy'd+12345
?Makes quantifiers 'lazy'd+?1 in 12345
*The * (zero or more) is 'greedy'A*AAA
?Makes quantifiers 'lazy'A*?empty in AAA
{2,4}Two to four times, 'greedy'w{2,4}abcd
?Makes quantifiers 'lazy'w{2,4}?ab in abcd

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Character Classes

CharacterLegendExampleSample Match
[ … ]One of the characters in the brackets[AEIOU]One uppercase vowel
[ … ]One of the characters in the bracketsT[ao]pTap or Top
-Range indicator[a-z]One lowercase letter
[x-y]One of the characters in the range from x to y[A-Z]+GREAT
[ … ]One of the characters in the brackets[AB1-5w-z]One of either: A,B,1,2,3,4,5,w,x,y,z
[x-y]One of the characters in the range from x to y[ -~]+Characters in the printable section of the ASCII table.
[^x]One character that is not x[^a-z]{3}A1!
[^x-y]One of the characters not in the range from x to y[^ -~]+Characters that are not in the printable section of the ASCII table.
[dD]One character that is a digit or a non-digit[dD]+Any characters, inc-
luding new lines, which the regular dot doesn't match
[x41]Matches the character at hexadecimal position 41 in the ASCII table, i.e. A[x41-x45]{3}ABE

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Anchors and Boundaries

AnchorLegendExampleSample Match
^Start of string or start of line depending on multiline mode. (But when [^inside brackets], it means 'not')^abc .*abc (line start)
$End of string or end of line depending on multiline mode. Many engine-dependent subtleties..*? the end$this is the end
ABeginning of string
(all major engines except JS)
Aabc[dD]*abc (string...
...start)
zVery end of the string
Not available in Python and JS
the endzthis is...n...the end
ZEnd of string or (except Python) before final line break
Not available in JS
the endZthis is...n...the endn
GBeginning of String or End of Previous Match
.NET, Java, PCRE (C, PHP, R…), Perl, Ruby
bWord boundary
Most engines: position where one side only is an ASCII letter, digit or underscore
Bob.*bcatbBob ate the cat
bWord boundary
.NET, Java, Python 3, Ruby: position where one side only is a Unicode letter, digit or underscore
Bob.*bкошкаbBob ate the кошка
BNot a word boundaryc.*BcatB.*copycats

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POSIX Classes

CharacterLegendExampleSample Match
[:alpha:]PCRE (C, PHP, R…): ASCII letters A-Z and a-z[8[:alpha:]]+WellDone88
[:alpha:]Ruby 2: Unicode letter or ideogram[[:alpha:]d]+кошка99
[:alnum:]PCRE (C, PHP, R…): ASCII digits and letters A-Z and a-z[[:alnum:]]{10}ABCDE12345
[:alnum:]Ruby 2: Unicode digit, letter or ideogram[[:alnum:]]{10}кошка90210
[:punct:]PCRE (C, PHP, R…): ASCII punctuation mark[[:punct:]]+?!.,:;
[:punct:]Ruby: Unicode punctuation mark[[:punct:]]+‽,:〽⁆

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Inline Modifiers

None of these are supported in JavaScript. In Ruby, beware of (?s) and (?m).
ModifierLegendExampleSample Match
(?i)Case-insensitive mode
(except JavaScript)
(?i)MondaymonDAY
(?s)DOTALL mode (except JS and Ruby). The dot (.) matches new line characters (rn). Also known as 'single-line mode' because the dot treats the entire input as a single line(?s)From A.*to ZFrom A
to Z
(?m)Multiline mode
(except Ruby and JS) ^ and $ match at the beginning and end of every line
(?m)1rn^2$rn^3$1
2
3
(?m)In Ruby: the same as (?s) in other engines, i.e. DOTALL mode, i.e. dot matches line breaks(?m)From A.*to ZFrom A
to Z
(?x)Free-Spacing Mode mode
(except JavaScript). Also known as comment mode or whitespace mode
(?x) # this is a
# comment
abc # write on multiple
# lines
[ ]d # spaces must be
# in brackets
abc d
(?n).NET, PCRE 10.30+: named capture onlyTurns all (parentheses) into non-capture groups. To capture, use named groups.
(?d)Java: Unix linebreaks onlyThe dot and the ^ and $ anchors are only affected by n
(?^)PCRE 10.32+: unset modifiersUnsets ismnx modifiers

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Lookarounds

LookaroundLegendExampleSample Match
(?=…)Positive lookahead(?=d{10})d{5}01234 in 0123456789
(?<=…)Positive lookbehind(?<=d)catcat in 1cat
(?!…)Negative lookahead(?!theatre)thew+theme
(?<!…)Negative lookbehindw{3}(?<!mon)sterMunster

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Character Class Operations

Class OperationLegendExampleSample Match
[…-[…]].NET: character class subtraction. One character that is in those on the left, but not in the subtracted class.[a-z-[aeiou]]Any lowercase consonant
[…-[…]].NET: character class subtraction.[p{IsArabic}-[D]]An Arabic character that is not a non-digit, i.e., an Arabic digit
[…&&[…]]Java, Ruby 2+: character class intersection. One character that is both in those on the left and in the && class.[S&&[D]]An non-whitespace character that is a non-digit.
[…&&[…]]Java, Ruby 2+: character class intersection.[S&&[D]&&[^a-zA-Z]]An non-whitespace character that a non-digit and not a letter.
[…&&[^…]]Java, Ruby 2+: character class subtraction is obtained by intersecting a class with a negated class[a-z&&[^aeiou]]An English lowercase letter that is not a vowel.
[…&&[^…]]Java, Ruby 2+: character class subtraction[p{InArabic}&&[^p{L}p{N}]]An Arabic character that is not a letter or a number

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Other Syntax

SyntaxLegendExampleSample Match
KKeep Out
Perl, PCRE (C, PHP, R…), Python's alternate regex engine, Ruby 2+: drop everything that was matched so far from the overall match to be returned
prefixKd+12
Q…EPerl, PCRE (C, PHP, R…), Java: treat anything between the delimiters as a literal string. Useful to escape metacharacters.Q(C++ ?)E(C++ ?)

Don't Miss The Regex Style Guide
and The Best Regex Trick Ever!!!

The 1001 ways to use Regex

1-10 of 17 Threads
Subject: Very thoughtful and useful cheat sheet

Unlike lots of other cheat sheets or regex web sites, I was able (without much persistent regex knowledge) to apply the rules and to solve my problem. THANK YOU :)
Subject: Thanks a lot

Thanks a lot for the quick guide. It's really helpful.
Subject: Very useful site

Thank you soooooo much for this site. I'm using python regex for natural language processing in sentiment analysis and this helped me a lot.
Subject: Thank you! Excellent resource for any student

Thank you so much for this incredible cheatsheet! It is facilitating a lot my regex learning! God bless you and your passion!
Subject: Thank you for doing such a geat work.

I am now learning regex and for finding such a well organized site is a blessing! You are a good soul! Thank you for everything and stay inspired!
Subject: Simple = perfect

Subject: Congratulations

Well done, very useful page. Thank you for your effort. T
Subject: Thank you very much

Hi Rex,
Thankyou very much for compiling these. I am new to text analytics and is struggling a lot with regex. This is helping me a lot pick up. Great work

Php Regular Expression Cheat Sheet

Subject: Nice summary
Php Regular Expression Cheat Sheet
Nice summary of regex. I was trying to remember how to group and I found the example above. Thanks.
Subject: Best Regex site ever

This is the best regex site ever on the internet. Regular Expressions are like any other language, they require time and effort to learn. RexEgg makes it an easy journey. Great work Author. Kudos to you.



Regular expressions are a powerful tool for examining and modifying text. Regular expressions themselves, with a general pattern notation almost like a mini programming language, allow you to describe and parse text. They enable you to search for patterns within a string, extracting matches flexibly and precisely. However, you should note that because regular expressions are more powerful, they are also slower than the more basic string functions. You should only use regular expressions if you have a particular need.

This tutorial gives a brief overview of basic regular expression syntax and then considers the functions that PHP provides for working with regular expressions.

PHP supports two different types of regular expressions: POSIX-extended and Perl-Compatible Regular Expressions (PCRE). The PCRE functions are more powerful than the POSIX ones, and faster too, so we will concentrate on them.

The Basics

In a regular expression, most characters match only themselves. For instance, if you search for the regular expression 'foo' in the string 'John plays football,' you get a match because 'foo' occurs in that string. Some characters have special meanings in regular expressions. For instance, a dollar sign ($) is used to match strings that end with the given pattern. Similarly, a caret (^) character at the beginning of a regular expression indicates that it must match the beginning of the string. The characters that match themselves are called literals. The characters that have special meanings are called metacharacters.

The dot (.) metacharacter matches any single character except newline (). So, the pattern h.t matches hat, hothit, hut, h7t, etc. The vertical pipe ( ) metacharacter is used for alternatives in a regular expression. It behaves much like a logical OR operator and you should use it if you want to construct a pattern that matches more than one set of characters. For instance, the pattern Utah Idaho Nevada matches strings that contain 'Utah' or 'Idaho' or 'Nevada'. Parentheses give us a way to group sequences. For example, (Nant b)ucket matches 'Nantucket' or 'bucket'. Using parentheses to group together characters for alternation is called grouping.

If you want to match a literal metacharacter in a pattern, you have to escape it with a backslash.

To specify a set of acceptable characters in your pattern, you can either build a character class yourself or use a predefined one. A character class lets you represent a bunch of characters as a single item in a regular expression. You can build your own character class by enclosing the acceptable characters in square brackets. A character class matches any one of the characters in the class. For example a character class [abc] matches a, b or c. To define a range of characters, just put the first and last characters in, separated by hyphen. For example, to match all alphanumeric characters: [a-zA-Z0-9]. You can also create a negated character class, which matches any character that is not in the class. To create a negated character class, begin the character class with ^: [^0-9].

The metacharacters +, *, ?, and {} affect the number of times a pattern should be matched. + means 'Match one or more of the preceding expression', * means 'Match zero or more of the preceding expression', and ? means 'Match zero or one of the preceding expression'. Curly braces {} can be used differently. With a single integer, {n} means 'match exactly n occurrences of the preceding expression', with one integer and a comma, {n,} means 'match n or more occurrences of the preceding expression', and with two comma-separated integers {n,m} means 'match the previous character if it occurs at least n times, but no more than m times'.

Now, have a look at the examples:

Regular ExpressionWill match...
fooThe string 'foo'
^foo'foo' at the start of a string
foo$'foo' at the end of a string
^foo$'foo' when it is alone on a string
[abc]a, b, or c
[a-z]Any lowercase letter
[^A-Z]Any character that is not a uppercase letter
(gif jpg)Matches either 'gif' or 'jpeg'
[a-z]+One or more lowercase letters
[0-9.-]Аny number, dot, or minus sign
^[a-zA-Z0-9_]{1,}$Any word of at least one letter, number or _
([wx])([yz])wy, wz, xy, or xz
[^A-Za-z0-9]Any symbol (not a number or a letter)
([A-Z]{3} [0-9]{4})Matches three letters or four numbers

Perl-Compatible Regular Expressions emulate the Perl syntax for patterns, which means that each pattern must be enclosed in a pair of delimiters. Usually, the slash (/) character is used. For instance, /pattern/.

The PCRE functions can be divided in several classes: matching, replacing, splitting and filtering.

Matching Patterns

The preg_match() function performs Perl-style pattern matching on a string. preg_match() takes two basic and three optional parameters. These parameters are, in order, a regular expression string, a source string, an array variable which stores matches, a flag argument and an offset parameter that can be used to specify the alternate place from which to start the search:

preg_match ( pattern, subject [, matches [, flags [, offset]]])

The preg_match() function returns 1 if a match is found and 0 otherwise. Let's search the string 'Hello World!' for the letters 'll':

<?php
if (preg_match('/ell/', 'Hello World!', $matches)) {
echo 'Match was found <br />';
echo $matches[0];
}
?>

The letters 'll' exist in 'Hello', so preg_match() returns 1 and the first element of the $matches variable is filled with the string that matched the pattern. The regular expression in the next example is looking for the letters 'ell', but looking for them with following characters:

<?php
if (preg_match('/ll.*/', 'The History of Halloween', $matches)) {
echo 'Match was found <br />';
echo $matches[0];
}
?>

Now let's consider more complicated example. The most popular use of regular expressions is validation. The example below checks if the password is 'strong', i.e. the password must be at least 8 characters and must contain at least one lower case letter, one upper case letter and one digit:

<?php
$password = 'Fyfjk34sdfjfsjq7';
if (preg_match('/^.*(?=.{8,})(?=.*d)(?=.*[a-z])(?=.*[A-Z]).*$/', $password)) {
echo 'Your passwords is strong.';
} else {
echo 'Your password is weak.';
}
?>

The ^ and $ are looking for something at the start and the end of the string. The '.*' combination is used at both the start and the end. As mentioned above, the .(dot) metacharacter means any alphanumeric character, and * metacharacter means 'zero or more'. Between are groupings in parentheses. The '?=' combination means 'the next text must be like this'. This construct doesn't capture the text. In this example, instead of specifying the order that things should appear, it's saying that it must appear but we're not worried about the order.

The first grouping is (?=.*{8,}). This checks if there are at least 8 characters in the string. The next grouping (?=.*[0-9]) means 'any alphanumeric character can happen zero or more times, then any digit can happen'. So this checks if there is at least one number in the string. But since the string isn't captured, that one digit can appear anywhere in the string. The next groupings (?=.*[a-z]) and (?=.*[A-Z]) are looking for the lower case and upper case letter accordingly anywhere in the string.

Finally, we will consider regular expression that validates an email address:

<?php
$email = [email protected];
$regexp = '/^[^0-9][A-z0-9_]+([.][A-z0-9_]+)*[@][A-z0-9_]+([.][A-z0-9_]+)*[.][A-z]{2,4}$/';
if (preg_match($regexp, $email)) {
echo 'Email address is valid.';
} else {
echo 'Email address is <u>not</u> valid.';
}
?>

This regular expression checks for the number at the beginning and also checks for multiple periods in the user name and domain name in the email address. Let's try to investigate this regular expression yourself.

For the speed reasons, the preg_match() function matches only the first pattern it finds in a string. This means it is very quick to check whether a pattern exists in a string. An alternative function, preg_match_all(), matches a pattern against a string as many times as the pattern allows, and returns the number of times it matched.

Replacing Patterns

In the above examples, we have searched for patterns in a string, leaving the search string untouched. The preg_replace() function looks for substrings that match a pattern and then replaces them with new text. preg_replace() takes three basic parameters and an additional one. These parameters are, in order, a regular expression, the text with which to replace a found pattern, the string to modify, and the last optional argument which specifies how many matches will be replaced.

preg_replace( pattern, replacement, subject [, limit ])

The function returns the changed string if a match was found or an unchanged copy of the original string otherwise. In the following example we search for the copyright phrase and replace the year with the current.

<?php
echo preg_replace('/([Cc]opyright) 200(3 4 5 6)/', '$1 2007', 'Copyright 2005');
?>

In the above example we use back references in the replacement string. Back references make it possible for you to use part of a matched pattern in the replacement string. To use this feature, you should use parentheses to wrap any elements of your regular expression that you might want to use. You can refer to the text matched by subpattern with a dollar sign ($) and the number of the subpattern. For instance, if you are using subpatterns, $0 is set to the whole match, then $1, $2, and so on are set to the individual matches for each subpattern.

In the following example we will change the date format from 'yyyy-mm-dd' to 'mm/dd/yyy':

<?php
echo preg_replace('/(d+)-(d+)-(d+)/', '$2/$3/$1', '2007-01-25');
?>

We also can pass an array of strings as subject to make the substitution on all of them. To perform multiple substitutions on the same string or array of strings with one call to preg_replace(), we should pass arrays of patterns and replacements. Have a look at the example:

<?php
$search = array ( '/(w{6}s(w{2})s(w+)/e',
'/(d{4})-(d{2})-(d{2})s(d{2}:d{2}:d{2})/');
$replace = array ('$1 '.strtoupper('$2')',
'$3/$2/$1 $4');
$string = 'Posted by John 2007-02-15 02:43:41';
echo preg_replace($search, $replace, $string);?>

In the above example we use the other interesting functionality - you can say to PHP that the match text should be executed as PHP code once the replacement has taken place. Since we have appended an 'e' to the end of the regular expression, PHP will execute the replacement it makes. That is, it will take strtoupper(name) and replace it with the result of the strtoupper() function, which is NAME.

Array Processing

PHP's preg_split() function enables you to break a string apart basing on something more complicated than a literal sequence of characters. When it's necessary to split a string with a dynamic expression rather than a fixed one, this function comes to the rescue. The basic idea is the same as preg_match_all() except that, instead of returning matched pieces of the subject string, it returns an array of pieces that didn't match the specified pattern. The following example uses a regular expression to split the string by any number of commas or space characters:

Php Regular Expression Cheat Sheet

<?php
$keywords = preg_split('/[s,]+/', 'php, regular expressions');
print_r( $keywords );
?>

Another useful PHP function is the preg_grep() function which returns those elements of an array that match a given pattern. This function traverses the input array, testing all elements against the supplied pattern. If a match is found, the matching element is returned as part of the array containing all matches. The following example searches through an array and all the names starting with letters A-J:

C# Regular Expressions Cheat Sheet

<?php
$names = array('Andrew','John','Peter','Nastin','Bill');
$output = preg_grep('/^[a-m]/i', $names);
print_r( $output );
?>