re: Regular Expression Utilities

Table of content


The re: module wraps Go’s regexp package. See the Go’s doc for supported regular expression syntax.

Function usages notations follow the same convention as the builtin module doc.

The following options are supported by multiple functions in this module:

  • &posix=$false: Use POSIX ERE syntax. See also doc in Go package.

  • &longest=$false: Prefer leftmost-longest match. See also doc in Go package.

  • &max=-1: If non-negative, limits the maximum number of results.



re:find &posix=$false &longest=$false &max=-1 $pattern $source

Find all matches of $pattern in $source.

Each match is represented by a map-like value $m; $m[text], $m[start] and $m[end] are the text, start and end positions (as byte indices into $source) of the match; $m[groups] is a list of submatches for capture groups in the pattern. A submatch has a similar structure to a match, except that it does not have a group key. The entire pattern is an implicit capture group, and it always appears first.


~> re:find . ab
▶ [&text=a &start=0 &end=1 &groups=[[&text=a &start=0 &end=1]]]
▶ [&text=b &start=1 &end=2 &groups=[[&text=b &start=1 &end=2]]]
~> re:find '[A-Z]([0-9])' 'A1 B2'
▶ [&text=A1 &start=0 &end=2 &groups=[[&text=A1 &start=0 &end=2] [&text=1 &start=1 &end=2]]]
▶ [&text=B2 &start=3 &end=5 &groups=[[&text=B2 &start=3 &end=5] [&text=2 &start=4 &end=5]]]


re:match &posix=$false $pattern $source

Determine whether $pattern matches $source. The pattern is not anchored. Examples:

~> re:match . xyz
▶ $true
~> re:match . ''
▶ $false
~> re:match '[a-z]' A
▶ $false


re:quote $string

Quote $string for use in a pattern. Examples:

~> re:quote a.txt
▶ a\.txt
~> re:quote '(*)'
▶ '\(\*\)'


re:replace &posix=$false &longest=$false &literal=$false $pattern $repl $source

Replace all occurrences of $pattern in $source with $repl.

The replacement $repl can be any of the following:

  • A string-typed replacement template. The template can use $name or ${name} patterns to refer to capture groups, where name consists of letters, digits and underscores. A purely numeric patterns like $1 refers to the capture group with the corresponding index; other names refer to capture groups named with the (?P<name>...)) syntax.

    In the $name form, the name is taken to be as long as possible; $1 is equivalent to ${1x}, not ${1}x; $10 is equivalent to ${10}, not ${1}0.

    To insert a literal $, use $$.

  • A function that takes a string argument and outputs a string. For each match, the function is called with the content of the match, and its output is used as the replacement.

If $literal is true, $repl must be a string and is treated literally instead of as a pattern.


~> re:replace '(ba|z)sh' '${1}SH' 'bash and zsh'
▶ 'baSH and zSH'
~> re:replace '(ba|z)sh' elvish 'bash and zsh rock'
▶ 'elvish and elvish rock'
~> re:replace '(ba|z)sh' {|x| put [&bash=BaSh &zsh=ZsH][$x] } 'bash and zsh'
▶ 'BaSh and ZsH'


re:split &posix=$false &longest=$false &max=-1 $pattern $source

Split $source, using $pattern as separators. Examples:

~> re:split : /usr/sbin:/usr/bin:/bin
▶ /usr/sbin
▶ /usr/bin
▶ /bin
~> re:split &max=2 : /usr/sbin:/usr/bin:/bin
▶ /usr/sbin
▶ /usr/bin:/bin