Regular expressions
Last updated: 5 Aug 2020 ·
Posted in wiki#notes
Character classes
| Character | Meaning |
|---|---|
. | Any character except newline |
\d | One digit |
\D | One non-digit |
\s | One whitespace |
\S | One non-whitespace |
\w | One word character |
\W | One non-word character |
\t | Horizontal tab |
\v | Vertical tab |
\r | Carriage return |
\n | Newline/Linefeed |
\f | Form-feed |
[\b] | Backspace character |
\0 | NUL character |
\ | Escape a special character |
Assertions
| Character | Meaning |
|---|---|
^ | Start of string |
$ | End of string |
\b | Word boundary |
\B | Non-word boundary |
x(?=y) | Positive lookahead (Matches "x" only if "x" is followed by "y") |
x(?!y) | Negative lookahead (Matches "x" only if "x" is not followed by "y") |
(?<=y)x | Positive lookbehind (Matches "x" only if "x" is preceded by "y") |
(?<!y)x | Negative lookbehind (Matches "x" only if "x" is not preceded by "y") |
Groups and ranges
| Character | Meaning |
|---|---|
x|y | Either "x" or "y" |
[xyz] [a-c] | Any one of the enclosed characters |
[^xyz] [^a-c] | Anything that is not enclosed in the brackets |
(x) | Capturing group (matches "x" and remembers the match) |
(?<Name>x) | Named capturing group (matches "x" and stores it as "Name") |
(?:x) | Non-capturing group (matches "x" but does not remember the match) |
\N | Match the Nth captured group |
\k<Name> | Back reference to the last substring matching the named capturing group specified by "Name" |
Quantifiers
| Character | Meaning |
|---|---|
* | 0 or more |
+ | 1 or more |
? | 0 or 1 |
x{n} | Exactly n occurences of x |
x{n, m} | Between n and m occurences of x |
x{n,} | n or more occurences of x |
? | Make the quantifier non-greedy (stop as soon as it finds a match) |
POSIX classes
| Character | Meaning |
|---|---|
[:alnum:] | Letters and digits |
[:alpha:] | Letters |
[:ascii:] | Ascii codes 0 - 127 |
[:blank:] | Space or tab only |
[:cntrl:] | Control characters |
[:digit:] | Decimal digits |
[:graph:] | Visible characters, except space |
[:upper:] | Uppercase letters |
[:lower:] | Lowercase letters |
[:word:] | Word characters |
[:print:] | Visible characters |
[:punct:] | Visible punctuation characters |
[:space:] | Whitespace |
[:xdigit:] | Hexadecimal digits |