Difference between revisions of "Regexp"
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Revision as of 09:53, 28 March 2012
Syntax
The following characters are special : . * + ? ^ $ \ [
Between brackets [], the following are special : ] - ^
Many characters are special when they follow a backslash – see below.
. any character (but newline) * previous character or group, repeated 0 or more time + previous character or group, repeated 1 or more time ? previous character or group, repeated 0 or 1 time ^ start of line $ end of line [...] any character between brackets [^..] any character not in the brackets [a-z] any character between a and z \ prevents interpretation of following special char \| or \w word constituent \b word boundary \sc character with c syntax (e.g. \s- for whitespace char) \( \) start\end of group \< \> start\end of word \` \' start\end of buffer \1 string matched by the first group \n string matched by the nth group \{3\} previous character or group, repeated 3 times \{3,\} previous character or group, repeated 3 or more times \{3,6\} previous character or group, repeated 3 to 6 times
.?, +?, and ?? are non-greedy versions of ., +, and ? \W, \B, and \Sc match any character that does not match \w, \b, and \sc
Character category
\ca ascii character \Ca non-ascii character (newline included) \cl latin character \cg greek character
POSIX character classes
[:digit:] a digit, same as [0-9] [:upper:] a letter in uppercase [:space:] a whitespace character, as defined by the syntax table [:xdigit:] an hexadecimal digit [:cntrl:] a control character [:ascii:] an ascii character
Syntax classes
\s- whitespace character \s/ character quote character \sw word constituent \s$ paired delimiter \s_ symbol constituent \s' expression prefix \s. punctuation character \s< comment starter \s( open delimiter character \s> comment ender \s) close delimiter character \s! generic comment delimiter \s" string quote character \s| generic string delimiter \s\ escape character
Regexp Examples
[-+[:digit:]] digit or + or - sign \(\+\|-\)?[0-9]+\(\.[0-9]+\)? decimal number (-2 or 1.5 but not .2 or 1.) \(\w+\) +\1\> two consecutive, identical words \<upper:\w* word starting with an uppercase letter +$ trailing whitespaces (note the starting SPC) \w\{20,\} word with 20 letters or more \w+phony\> word ending by phony \(19\|20\)[0-9]\{2\} year 1900-2099 ^.\{6,\} at least 6 symbols ^[a-zA-Z0-9_]\{3,16\}$ decent string for a user name <tag[^> C-q C-j ]*>\(.*?\)</tag> html tag
Emacs Commands that Use Regular Expressions
C-M-s incremental forward search matching regexp C-M-r incremental backward search matching regexp replace-regexp replace string matching regexp query-replace-regexp same, but query before each replacement align-regexp align, using strings matching regexp as delimiters highlight-regexp highlight strings matching regexp occur show lines containing a match multi-occur show lines in all buffers containing a match how-many count the number of strings matching regexp keep-lines delete all lines except those containing matches flush-lines delete lines containing matches grep call unix grep command and put result in a buffer lgrep user-friendly interface to the grep command rgrep recursive grep dired-do-copy-regexp copy files with names matching regexp dired-do-rename-regexp rename files matching regexp find-grep-dired display files containing matches for regexp with Dired
See Also
Re-builder build regexp interactively in buffer