PHP regex/I,/s,/x,/u,/u,/A,/D,/s, etc. pattern modifiers

I (pcre_caseless)

If this modifier is set , the letters in the pattern are case insensitive and match .

m (pcre_multiline)

By default, pcre that the target string is made up of one-line characters(However, it may actually contain multiple lines), "beginning "meta character (^) matches only the starting position of the string ,  and " end "meta-character ($) matches only the end of the string ,  or the last newline character is set d Modifier perl the same .  when this modifier is set " and "end " will match any newline character in the target string before or after the Span lang= "en-US" >,  in addition ,  also match the first and last position of the target string .  this equates to perl /m modifier .  if the target string   does not have ,  or mode does not appear ^ or $,  settings this modifier has no effect

s (pcre_dotall)

If this modifier is set , the dot character in the pattern matches all characters , including line breaks . If you do not have this modifier , the dot number does not match the line break . This modifier is equivalent to the/ s modifier in Perl . An inverse character class such as [^a] always matches a newline character , and does not depend on the modifier's settings .

x (pcre_extended)

If this modifier is set , the non-escaped or blank data characters in the pattern are always ignored and are located outside of an escaped character class #字符和下一个换行符之间的字符也被忽略. This modifier is equivalent to The /x modifier in Perl , which allows comments to be included in the compiled mode . Note : This is used only for data characters . Whitespace characters cannot appear in a special sequence of characters in a pattern , such as a sequence (? A conditional subgroup was introduced ( This syntax defines a special character sequence in which a white-space character causes a compilation error .) such as (? ( will cause errors .).

e (preg_replace_eval)

If this modifier is set , Preg_replace () is replaced with a back reference to the replacement string , evaluates the replacement string as a PHP code (eval function ), and uses the execution result As a string that actually participates in the substitution . Single quotes , double quotes , backslashes (\), and null characters are escaped with a backslash when the back reference is replaced .

Tip

Make sure that the replacement parameter is made up of a valid PHP code string , otherwise PHP will generate an explanatory error on the line called Preg_replace () .

Note : Only preg_replace () uses this modifier , and the other pcre function ignores this modifier .

A (pcre_anchored)

If this modifier is set , the pattern is coerced to "anchored " mode, which means that the constraint matches the search only from the beginning of the target string . This effect can also be constructed using the appropriate pattern , and this is the only way for Perl to implement this pattern .

D (pcre_dollar_endonly)

If this modifier is set , the meta-character dollar sign in the pattern matches only the end of the target string . If this modifier is not set , the dollar sign also matches the newline character if the string ends with a newline character (but does not match any previous line break ). If the modifier mis set, this modifier is ignored . There is no modifier equivalent to this modifier in Perl .

S

When a pattern needs to be used more than once, it is worth taking some time to perform some additional analysis in order to get a match speed boost. If this modifier is set , this additional analysis will be performed . Currently , This analysis of a pattern only applies to non-anchored pattern matching (that is, there is no separate fixed-start character ).

U (pcre_ungreedy)

This modifier reverses the "greedy " pattern of quantifiers . Make quantifiers default to non-greedy , followed by quantifiers ? Way to make it greedy . This is incompatible with Perl . It can also be set using the pattern modifier (? U) , or mark its non-greed with a question mark after the quantifier (e.g. . *? ).

Note :

In non-greedy mode , characters that exceed pcre.backtrack_limit are usually not matched.

X (Pcre_extra)

This modifier opens the pcre and perl incompatible attachments feature . After any backslash in the pattern, ingen a character with no special meaning causes an error that preserves these characters for backward compatibility . By default , in Perl , a backslash followed by a character with no special meaning is considered to be the original of the character . No other feature is currently controlled by this modifier .

J (pcre_info_jchanged)

Internal option settings (? J) Modify the local pcre_dupnames option. Allows the name of the child group . ( Note: The external/j setting generates an error only through the internal option setting .)

u (PCRE8)

This modifier opens an additional feature that is incompatible with Perl . The pattern string is considered utf-8 . This modifier is from the Unix version of php 4.1.0 or higher , and the Win32 version of PHP 4.2.3 begins to be available . PHP 4.3.5 starts checking the utf-8 legitimacy of the pattern. This modifier turns on additional functionality of PCRE, that's incompatible with Perl. Pattern strings is treated as UTF-8. This modifier was available from PHP 4.1.0 or greater on Unix and from PHP 4.2.3 on Win32. UTF-8 validity of the pattern is checked since PHP 4.3.5.

Transferred from: http://blog.csdn.net/cjsyr_cjsyr/article/details/53688984

PHP regex/I,/s,/x,/u,/u,/A,/D,/s, etc. pattern modifiers