PHP正規表現関数
PHP正規表現の紹介
正規表現を使用すると、文字列内のパターンを検索して置き換えることができます。
インストール
PHPの正規表現関数は、PHPコアの一部です。これらの機能を使用するためにインストールは必要ありません。
ランタイム構成
php.iniのこれらの設定を使用して、正規表現を評価するときに使用する時間またはリソースを制限できます。
| Name | Default | Description | Changeable |
|---|---|---|---|
| pcre.backtrack_limit | "1000000" | The maximum number of backtracks that the regular expression engine is allowed to do while evaluating an expression. (available since PHP 5.2) | PHP_INI_ALL |
| pcre.recursion_limit | "100000" | The maximum recursion depth that the regular expression engine is permitted to reach while evaluating an expression. (available since PHP 5.2) | PHP_INI_ALL |
| pcre.jit | "1" | When set to "1" this enables PCRE's (Perl-Compatible Regular Expressions) just-in-time compilation. (available since PHP 7.0) | PHP_INI_ALL |
PHP正規表現関数
| Function | Description |
|---|---|
| preg_filter() | Returns a string or an array with pattern matches replaced, but only if matches were found |
| preg_grep() | Returns an array consisting only of elements from the input array which matched the pattern |
| preg_last_error() | Returns an error code indicating the reason that the most recent regular expression call failed |
| preg_match() | Finds the first match of a pattern in a string |
| preg_match_all() | Finds all matches of a pattern in a string |
| preg_replace() | Returns a string where matches of a pattern (or an array of patterns) are replaced with a substring (or an array of substrings) in a given string |
| preg_replace_callback() | Given an expression and a callback, returns a string where all matches of the expression are replaced with the substring returned by the callback |
| preg_replace_callback_array() | Given an array associating expressions with callbacks, returns a string where all matches of each expression are replaced with the substring returned by the callback |
| preg_split() | Breaks a string into an array using matches of a regular expression as separators |
| preg_quote() | Escapes characters that have a special meaning in regular expressions by putting a backslash in front of them |
正規表現修飾子
修飾子は、検索の実行方法を変更できます。
| Modifier | Description |
|---|---|
| i | Performs a case-insensitive search |
| m | Performs a multiline search (patterns that search for the beginning or end of a string will match the beginning or end of each line) |
| u | Enables correct matching of UTF-8 encoded patterns |
正規表現パターン
角かっこは、文字の範囲を見つけるために使用されます。
| Expression | Description |
|---|---|
| [abc] | Find one character from the options between the brackets |
| [^abc] | Find any character NOT between the brackets |
| [0-9] | Find one character from the range 0 to 9 |
メタ文字
メタ文字は、特別な意味を持つ文字です。
| Metacharacter | Description |
|---|---|
| | | Find a match for any one of the patterns separated by | as in: cat|dog|fish |
| . | Find just one instance of any character |
| ^ | Finds a match as the beginning of a string as in: ^Hello |
| $ | Finds a match at the end of the string as in: World$ |
| \d | Find a digit |
| \s | Find a whitespace character |
| \b | Find a match at the beginning of a word like this: \bWORD, or at the end of a word like this: WORD\b |
| \uxxxx | Find the Unicode character specified by the hexadecimal number xxxx |
量指定子
数量詞は数量を定義します。
| Quantifier | Description |
|---|---|
| n+ | Matches any string that contains at least one n |
| n* | Matches any string that contains zero or more occurrences of n |
| n? | Matches any string that contains zero or one occurrences of n |
| n{x} | Matches any string that contains a sequence of X n's |
| n{x,y} | Matches any string that contains a sequence of X to Y n's |
| n{x,} | Matches any string that contains a sequence of at least X n's |
注：式で特殊文字の1つを検索する必要がある場合は、円記号（\）を使用してそれらをエスケープできます。たとえば、1つ以上の疑問符を検索するには、次の式を使用できます。$ pattern = '/ \？+ /';