Some PHP regular expression learning PHP regular expression basic syntax application learning.
^ Start
$ End
* Match zero or more
"AB *" matches strings a and 0 or more B ("a" "AB" abb "" abbbbbb "etc)
+ Match one or more
The difference between "AB +" matching string a and a string ("AB" abb "" abbbbbb "etc) consisting of one or more bits is that * must be followed by B.
? Matches zero or one
"AB? "Match 0 or a B (" a "," AB ")
.*? It is often used to match a large string, that is, a string that does not need to be matched, that is, to directly think about it.
Example:
"? B + $ "match one or zero a and add more than one string ending with B (" B "" AB "" bbbbb "" abbbbbbbbb ")
Of course, you can also add a limit on the number of characters in the braces.
"AB {2}" a must be followed by two B, that is, "abb"
"AB {2,}" B after matching a must be greater than or equal to two "abb" "abbb" "abbbbb"
"AB {}" matches B after a between 2 and 5 "abb" "abbb" "abbbb" "abbbbb"
But less than two bits cannot be like this. "AB {, 2}" must be like this. "AB }"
So
* It is equivalent to {0 ,}
+ Equivalent to {1 ,}
? Equivalent to {0, 1}
() Is to link some strings for matching
"A (bc) *" is to match a and then follow 0 bc or multiple bc "a" "abc" "abcbc" "abcbcbc" etc
| This character is equivalent to the OR operation.
"Hi | hello" matches strings that contain hi or hello
"(B | cd) ef" matches strings containing bef or cdef
"(A | c) * d" matches "d" ad "" cd "" aab "" ccd "" aaaaaaad "" cccccccccd"
. Can represent all single characters
"A. [0-9]" can match a and then end with a string with a number "aj9" "a <8". it can be any single character in the middle.
"^. {3} $" the "asd" that starts and ends with three single characters cannot be matched with any other three single characters, such as "kjl ."
[] This symbol contains only one character.
"[AB]" means that only matching a single a or a single B is equivalent to "a | B"
"[A-z]" matches 26 lower-case letters.
"^ [A-zA-Z]" matches a string starting with a letter
"[0-9] %" is to match a string containing x %.
", [A-zA-Z0-9] $" match a comma and then add a string ending with a number or letter ", 0" ", a" etc"
Some common replacement symbols in PHP
# Or // indicates the escape character for a single separator/
\ S indicates matching blank items
\ D matches a numeric character
\ W matches any word characters including underscores
The syntaxes summarized by the online experts are comprehensive.
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