PHP regular modifier usage example analysis

This article mainly introduces the usage of PHP regular modifiers, and analyzes the functions, usage methods and related precautions of PHP regular modifiers in detail in the form of examples. Friends in need can refer to the following

Examples of this article Learned the usage of php regular modifiers. Share it with everyone for your reference, the details are as follows:

Modifier:

POSIXCompatible regular expressions have no modifiers.

Perl compatible modifiers that may be used in regular expressions (spaces and newlines in the modifiers are ignored, other characters will cause errors):

i (PCRE_CASELESS):
Ignore case when matching.

m (PCRE_MULTILINE):
When this modifier is set, the start of line (^) and the end of line ($) match the beginning and end of the entire string. Also matches after and before the newline character (\n).

s (PCRE_DOTALL):
If this modifier is set, the dot metacharacter (.) in the pattern matches all characters, including newlines. Without this setting, newline characters are not included.

x (PCRE_EXTENDED):
If this modifier is set, whitespace characters in the pattern are completely ignored except those that are escaped or within a character class.

e :
If this modifier is set, preg_replace() performs the normal replacement of the backreference in the replacement string, evaluates it as PHP code, and uses The result is used to replace the searched string. Only preg_replace() uses this modifier, other PCRE functions ignore it.

A (PCRE_ANCHORED):
If this modifier is set, the pattern is forced to be "anchored", that is, it is forced to match only from the beginning of the target string.

D (PCRE_DOLLAR_ENDONLY):
If this modifier is set, the end of line ($) in the pattern only matches the end of the target string. Without this option, if the last character is a newline character, it will also be matched. This option is ignored if the m modifier is set.

S ​​:
When a pattern will be used several times, it is worth analyzing it first in order to speed up matching. If this modifier is set additional analysis will be performed. Currently, analyzing a pattern is only useful for non-anchored patterns that do not have a single fixed starting character.

U (PCRE_UNGREEDY):
Make the default matching of "?" greedy.

X (PCRE_EXTRA): Any backslash in the
pattern followed by a letter with no special meaning results in an error, thus preserving this combination for future extensions. By default, a backslash followed by a letter with no special meaning is treated as the letter itself.

u (PCRE_UTF8):
The pattern string is treated as UTF-8.

Note:

## Pattern Modifiers

i ——Can match both uppercase and lowercase letters
M ——Treat the string as multiple lines
S ​​ ——Treat the string as a single line, and use newline characters as ordinary characters Treat, making "." match any character
X - Blanks in the pattern are ignored
U - Match the nearest string
e -Use the replaced string as an expression

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