PHP regular expression summary_PHP tutorial

can be used as a wildcard character to replace any character except the newline character (n). For example, the regular expression:
.at
can match "cat", "sat", "#at", "mat", etc. Mainly used when searching for files

can also specify a character set:
[a-z]at
in The content in square brackets ([]) is a character class---a set of characters to which the matched characters belong. But only matches one of the characters.

At the same time, we can also give a set.
[aeiou]
can be used to represent vowels.

can also be used to represent a range. It can also be a range set:
[a-zA-Z]
This range set represents any large or small letters.

In addition, sets can also be used to indicate that characters do not belong to a certain set. For example:
[^a-z]
can be used to match any character that is not between a and z. When the radical symbol (^) is included in square brackets, it means no.

Number of repetitions
"*" means that this pattern can be repeated 0 or more times, and the symbol "+" means that this pattern can be repeated 1 or more times.

[[:alnum:]]+
means at least one letter.

The subexpression
(very)*large
can match very large, large, very very large, etc.

Subexpression count
You can use a numeric expression within curly braces ({}) to specify the number of times content is allowed to be repeated. You can specify an exact number ({3} means repeat 3 times), or a range of repetitions

({2,4} means repeat 2~4 times), or An open-ended repeat range ({2,} means it must be repeated at least 2 times).
For example:
(very){1,3}
means matching "very", "very very", "very very very".

Position to the beginning or end of the string
The caret (^) is used at the beginning of the regular expression to indicate that the substring must appear before The character "$" is used at the end of the regular expression at the beginning of the search string. Indicates that the substring must

appear at the end of the string.

For example, the following is matching bob at the beginning of the string:
^bob

This pattern will Matches strings where com appears at the end of the string:
com$

Finally, this pattern will match only one character from a to z The string:
^[a-z]$

branch

can be used in regular expressions A vertical line represents a selection. For example, if you want to match com, edu or net, you can use the following expression:
com|edu|net

matches special characters

If you want to match special characters, such as ., { or $, you must add a backslash () in front of them. If you want to match a backslash, you must use two backslashes (\) to express it.

In PHP, the regular expression pattern must be enclosed in a single quote character In the string.

In POSIX regular expressions, a summary of the special characters outside the square brackets
character meaning
                                                                                                                                                                                                                                               . or more times
$ at the end of the string Matching +repeated or more
. Matching characters other than the change character (n) {minimum/maximum number of marks
| Select the branch of the branch Beginning (or) of min/max tokens } End of min/max tokens
( Beginning of subpattern ? ? Marking a subpattern as optional
In POSIX regular expressions, the special characters used in square brackets

characters meaning
escape characters
^ No, only used at the beginning position
- Used to specify the character range

http://www.bkjia.com/PHPjc/440420.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/440420.htmlTechArticleYou can use characters as a wildcard character to replace any character except the newline character (n). For example, the regular expression: .at can match "cat", "sat", "#at", "mat", etc. Mainly...