How to use special characters in Perl pattern matching
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Special characters in Perl pattern matching
1.1 "+"
+ is used to match the preceding character with the following character at least once, or any time. Similar to windows * for example, dog,dogg,dooooog/ab+/ that / d+g/ can match will match abb, not ab, in the string abbc.
1.2 [] and [^]
[] means to match one of a set of characters
^ represents all characters except them
For example, / w [abcd] s / was,wbs,wcs,wds that can match
/ w [^ ab] s / mismatched was,wbs
It can also be written in the following form
/ w [a-z0-9A-Z] s /
1.3 characters * and?
They are similar to + except that * matches 0, 1 or more of the same characters,? Matches 0 or 1 of the character.
For example, / de*f/ matches df, def, deeeef, and so on; / de?f/ matches df or def.
1.4 position wildcard (anchor mode)
^ or\ An only matches the string head.
$or\ Z only matches the tail
\ b match word boundaries
\ B word internal matching
For example: / ^ def/ only matches strings that start with def, / $def/ only matches strings that end in def, and the combined / ^ def$/ matches only the string def (?). \ An and\ Z are different from ^ and $when multiple lines match.
\ b match at word boundaries: /\ bdef/ matches words such as def and defghi that start with def, but does not match abcdef. / def\ b / matches words that end in def, such as def and abcdef, but does not match defghi,/\ bdef\ b / matches only the string def. Note: /\ bdef/ matches $defghi because $is not considered part of the word.
\ B match inside the words: /\ Bdef/ matches abcdef, etc., but does not match def;/def\ B / match defghi, etc.; /\ Bdef\ B / matches cdefg, abcdefghi, etc., but does not match def,defghi,abcdef.
Character escape class in 1.5Perl pattern matching
\ d any number [0-9]
\ d any character except a number [^ 0-9]
\ w any word character [_ 0-9a-zA-Z]
\ W any non-word character [^ _ 0-9a-zA-Z]
\ s blank [\ r\ t\ n\ f]
\ s is not blank [^\ r\ t\ n\ f]
1.6 "."
Character "." Matches all characters except line breaks, usually in conjunction with *.
Matches a specified number of characters in 1.7Perl pattern matching
Character pair {} specifies the number of occurrences of matched characters.
For example: / de {1pr 3} f / match def,deef and deeef
/ de {3} f / match deeef
/ de {3,} f / match no less than 3 e between d and f
/ de {0Pert 3} f / matches no more than 3 e between d and f.
1.8 specify options
The character "|" specifies two or more selections to match the pattern. For example, / def | ghi/ matches def or ghi.
These escape characters have a certain order of operation:
() Mode memory
+ *? {} occurrence times
^ $\ b\ B anchor
| | options |
Pattern order variables in 1.9Perl pattern matching
The result of calling the reuse part after Perl pattern matching is available with the variable $n, and all results with the variable $&.
$string= "Thisstringcontainsthenumber25.11."
$string=~/-? (\ d +)\.? (\ d +) /; # matching result is 25.11
$integerpart=$1;#now$integerpart=25
$decimalpart=$2;#now$decimalpart=11
$totalpart=$&;#nowtotalpart=25.11
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