Getting Started With Php Regular Expressions, Php Preg_Match()

In this tutorial you will learn how regular expressions work, as well as how to lớn use them lớn perform pattern matching in an efficient way in PHP.

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What is Regular Expression

Regular Expressions, commonly known as "regex" or "RegExp", are a specially formatted text strings used khổng lồ find patterns in text. Regular expressions are one of the most powerful tools available today for effective & efficient text processing and manipulations. For example, it can be used to lớn verify whether the format of data i.e. Name, email, phone number, etc. Entered by the user was correct or not, find or replace matching string within text content, và so on.

PHP (version 5.3 and above) supports Perl style regular expressions via its preg_ family of functions. Why Perl style regular expressions? Because Perl (Practical Extraction và Report Language) was the first mainstream programming language that provided integrated tư vấn for regular expressions và it is well known for its strong support of regular expressions và its extraordinary text processing và manipulation capabilities.

Let"s begin with a brief overview of the commonly used PHP"s built-in pattern-matching functions before delving deep into the world of regular expressions.


FunctionWhat it Does
preg_match()Perform a regular expression match.
preg_match_all()Perform a global regular expression match.
preg_replace()Perform a regular expression search and replace.
preg_grep()Returns the elements of the input array that matched the pattern.
preg_split()Splits up a string into substrings using a regular expression.
preg_quote()Quote regular expression characters found within a string.

Note: The PHP preg_match() function stops searching after it finds the first match, whereas the preg_match_all() function continues searching until the end of the string and find all possible matches instead of stopping at the first match.


Regular Expression Syntax

Regular expression syntax includes the use of special characters (do not confuse with the HTML special characters). The characters that are given special meaning within a regular expression, are: . * ? + < > ( ) ^ $ | . You will need lớn backslash these characters whenever you want to lớn use them literally. For example, if you want khổng lồ match ".", you"d have khổng lồ write .. All other characters automatically assume their literal meanings.

The following sections describe the various options available for formulating patterns:

Character Classes

Square brackets surrounding a pattern of characters are called a character class e.g. . A character class always matches a single character out of a danh sách of specified characters that means the expression matches only a, b or c character.

Negated character classes can also be defined that match any character except those contained within the brackets. A negated character class is defined by placing a caret (^) symbol immediately after the opening bracket, like this <^abc>.

You can also define a range of characters by using the hyphen (-) character inside a character class, like <0-9>. Let"s look at some examples of character classes:


RegExpWhat it Does
Matches any one of the characters a, b, or c.
<^abc>Matches any one character other than a, b, or c.
Matches any one character from lowercase a lớn lowercase z.
Matches any one character from uppercase a to uppercase z.
Matches any one character from lowercase a to uppercase Z.
<0-9>Matches a single digit between 0 & 9.
Matches a single character between a and z or between 0 & 9.

The following example will show you how lớn find whether a pattern exists in a string or not using the regular expression and PHP preg_match() function:


ExampleRun this code »
Similarly, you can use the preg_match_all() function to find all matches within a string:


ExampleRun this code »
Tip: Regular expressions aren"t exclusive to PHP. Languages such as Java, Perl, Python, etc. Use the same notation for finding patterns in text.


Predefined Character Classes

Some character classes such as digits, letters, và whitespaces are used so frequently that there are shortcut names for them. The following table lists those predefined character classes:


ShortcutWhat it Does
.Matches any single character except newline .

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dmatches any digit character. Same as <0-9>
DMatches any non-digit character. Same as <^0-9>
sMatches any whitespace character (space, tab, newline or carriage return character). Same as < >
SMatches any non-whitespace character. Same as <^ >
wMatches any word character (definned as a to z, A to Z,0 to 9, & the underscore). Same as
WMatches any non-word character. Same as <^a-zA-Z_0-9>

The following example will show you how khổng lồ find và replace space with a hyphen character in a string using regular expression & PHP preg_replace() function:


Repetition Quantifiers

In the previous section we"ve learnt how to lớn match a single character in a variety of fashions. But what if you want to match on more than one character? For example, let"s say you want to lớn find out words containing one or more instances of the letter p, or words containing at least two p"s, và so on. This is where quantifiers come into play. With quantifiers you can specify how many times a character in a regular expression should match.

The following table lists the various ways to lớn quantify a particular pattern:


RegExpWhat it Doesp2,
p+Matches one or more occurrences of the letter p.
p*Matches zero or more occurrences of the letter p.
p?Matches zero or one occurrences of the letter p.
p2Matches exactly two occurrences of the letter p.
p2,3Matches at least two occurrences of the letter p, but not more than three occurrences of the letter p.
Matches two or more occurrences of the letter p.
p,3Matches at most three occurrences of the letter p

The regular expression in the following example will splits the string at comma, sequence of commas, whitespace, or combination thereof using the PHP preg_split() function:


Position Anchors

There are certain situations where you want to lớn match at the beginning or kết thúc of a line, word, or string. To vị this you can use anchors. Two common anchors are caret (^) which represent the start of the string, và the dollar ($) sign which represent the kết thúc of the string.


RegExpWhat it Does
^pMatches the letter p at the beginning of a line.
p$Matches the letter p. At the over of a line.

The regular expression in the following example will display only those names from the names array which start with the letter "J" using the PHP preg_grep() function:


Pattern Modifiers

A pattern modifier allows you lớn control the way a pattern match is handled. Pattern modifiers are placed directly after the regular expression, for example, if you want to search for a pattern in a case-insensitive manner, you can use the i modifier, lượt thích this: /pattern/i. The following table lists some of the most commonly used pattern modifiers.


ModifierWhat it Does
iMakes the match case-insensitive manner.
mChanges the behavior of ^ and $ to match against a newline boundary (i.e. Start or kết thúc of each line within a multiline string), instead of a string boundary.
gPerform a global match i.e. Finds all occurrences.
oEvaluates the expression only once.
sChanges the behavior of . (dot) to match all characters, including newlines.
xAllows you khổng lồ use whitespace and comments within a regular expression for clarity.

The following example will show you how lớn perform a global case-insensitive search using the i modifier và the PHP preg_match_all() function.


Similarly, the following example shows how khổng lồ match at the beginning of every line in a multi-line string using ^ anchor và m modifier with PHP preg_match_all() function.


Word Boundaries

A word boundary character ( ) helps you tìm kiếm for the words that begins and/or ends with a pattern. For example, the regexp /car/ matches the words beginning with the pattern car, và would match cart, carrot, or cartoon, but would not match oscar.

Similarly, the regexp /car/ matches the words ending with the pattern car, và would match scar, oscar, or supercar, but would not match cart. Likewise, the /car/ matches the words beginning & ending with the pattern car, and would match only the word car.

The following example will highlight the words beginning with oto in bold:


$0";$text = "Words begining with car: cart, carrot, cartoon. Words ending with car: scar, oscar, supercar.";echo preg_replace($pattern, $replacement, $text);?>
We hope you have understood the basics of regular expression. Lớn learn how to validate size data using regular expression, please kiểm tra out the tutorial on PHP size Validation.


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