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:awk &sep='[ \t]+' &sep-posix=$false &sep-longest=$false $f $inputs?

For each value input, calls $f with the input followed by all its fields.

The &sep option is a regular expression for the field separator. For the &sep-posix and &sep-longest options, see the introduction; the sep- prefix is added for clarity.

Calling break in $f exits both $f and re:awk, and can be used to stop processing inputs early. Calling continue exits $f but not re:awk, and can be used to stop $f early but continue processing inputs.

This command allows you to write code resembling AWK scripts, using an anonymous function instead of a string containing AWK code. A simple example:

~> echo " lorem ipsum\n1 2" | awk '{ print $1 }'
~> echo " lorem ipsum\n1 2" | re:awk {|line a b| put $a }
▶ lorem
▶ 1

Note: Since Elvish allows variable names consisting solely of digits, you can do something like this to emulate AWK even more closely:

~> echo " lorem ipsum\n1 2" | re:awk {|0 1 2| put $1 }
▶ lorem
▶ 1

If the number of fields differ between lines, use a rest argument:

~> echo "a b\nc d e" | re:awk {|@a| echo (- (count $a) 1)' fields' }
2 fields
3 fields

This command is roughly equivalent to the following Elvish function:

fn my-awk {|&sep='[ \t]+' &sep-posix=$false &sep-longest=$false f @rest|
  each {|line|
    var @fields = (re:split $sep &posix=$sep-posix &longest=$sep-longest (str:trim $line " \t"))
    $f $line $@fields
  } $@rest


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


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