In programming you quite often want to test a string for the occurrence of a character or group of characters.\u00a0 This is particularly true for such things as data validation on form input boxes.\u00a0 Regular expressions provide a pattern matching facility.<\/p>\n
This tutorial gives a brief overview of basic regular expression syntax and then considers the functions that PHP provides for
\nworking with regular expressions.<\/p>\n
The Basics
\nMatching Patterns
\nReplacing Patterns
\nArray Processing<\/p>\n
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.<\/p>\n
The Basics <\/strong><\/p>\n In a regular expression, most characters match only themselves. For instance, if you search for the regular expression “ball” in the string “John plays football,” you get a match because “ball” 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 (^) 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.<\/p>\n For example :<\/p>\n (Nant|b)ucket matches “Nantucket” or “bucket”. Using parentheses to group together characters for alternation is called grouping.<\/p>\n If you want to match a literal metacharacter in a pattern, you have to escape it with a backslash.<\/p>\n To specify a set of acceptable characters in your pattern, you can either build a character class yourself or use a predefined one.<\/p>\n 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 metacharacters +, *, ?, and {} affect the number of times a pattern should be matched. + means “Match one or more of the Now, have a look at the examples:<\/p>\n Regular Expression \u00a0\u00a0 \u00a0Will match… 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\/.<\/p>\n The PCRE functions can be divided in several classes: matching, replacing, splitting and filtering.<\/p>\n","protected":false},"excerpt":{"rendered":" In programming you quite often want to test a string for the occurrence of a character or group of characters.\u00a0 This is particularly true for such things as data validation on form input boxes.\u00a0 Regular expressions provide a pattern matching…<\/span><\/p>\n
\ncharacter at the beginning of a regular expression indicates that it must match the beginning of the string. The characters that
\nmatch themselves are called literals. The characters that have special meanings are called metacharacters.<\/p>\n
\nthe class. For example a character class [abc] matches a, b or c. To define a range of characters, just put the first and last
\ncharacters 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].<\/p>\n
\npreceding 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”.<\/p>\n
\nfoo \u00a0\u00a0 \u00a0The string “foo”
\n^foo \u00a0\u00a0 \u00a0“foo” at the start of a string
\nfoo$ \u00a0\u00a0 \u00a0“foo” at the end of a string
\n^foo$ \u00a0\u00a0 \u00a0“foo” when it is alone on a string
\n[abc] \u00a0\u00a0 \u00a0a, b, or c
\n[a-z] \u00a0\u00a0 \u00a0Any lowercase letter
\n[^A-Z] \u00a0\u00a0 \u00a0Any character that is not a uppercase letter
\n(gif|jpg) \u00a0\u00a0 \u00a0Matches either “gif” or “jpeg”
\n[a-z]+ \u00a0\u00a0 \u00a0One or more lowercase letters
\n[0-9\\.\\-] \u00a0\u00a0 \u00a0?ny number, dot, or minus sign
\n^[a-zA-Z0-9_]{1,}$ \u00a0\u00a0 \u00a0Any word of at least one letter, number or _
\n([wx])([yz]) \u00a0\u00a0 \u00a0wy, wz, xy, or xz
\n[^A-Za-z0-9] \u00a0\u00a0 \u00a0Any symbol (not a number or a letter)
\n([A-Z]{3}|[0-9]{4}) \u00a0\u00a0 \u00a0Matches three letters or four numbers<\/p>\n