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regex

Definition: include builtins\regex.e

sequence m = regex(sequence re, string target, integer strtndx=1)
Description: Applies the regular expression re (in string or pre-compiled format) to target and returns an array of group indexes or {} if no match could be found.

re: a regular expression such as "a(b*)" or the result of applying regex_compile() to such a string.
target: a string to be matched against the regular expression.
strtndx: obviously a non-1 value of n skips the first n-1 characters of target and can be significantly faster than repeatedly passing ever-decreasing slices of target and at the same time having to add an offset to any results.

Returns: an even-length sequence of group indexes, or {} if no match could be found.

The results, corresponding to \0, \1, \2, etc of regular expression afficionado parlance, are start/end pairs.
pwa/p2js: Supported.
Example 1: 
?regex(`(a)(bc)`,"abc") -- yields {1,3, 1,1, 2,3}

The result is 3 pairs of start/end indexes, which can be read as {target[1..3],target[1..1],target[2..3]} which in this case is {"abc","a","bc"}. The first element, aka `\0` is the entire match, the second aka `\1` from `(a)` is "a", and obviously the third aka `\2` from `(bc)` is "bc".
Example 2: 
string target = "abc"
sequence res = regex(`(a)(bc)`,target) -- res is {1,3, 1,1, 2,3}
if res!={} then
    sequence capture_groups = {}
    for i=1 to length(res) by 2 do
        integer {s,e} = res[i..i+1]
        capture_groups = append(capture_groups,target[s..e])
    end for
    -- capture_groups is now {"abc","a","bc"}
end if

Obviously, in most cases, only one capture group exists or only one is of any interest, and such a loop would be overkill.
See Also: regex syntax
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