What does "matches x and remembers the match" means in regexp

Question

Pardon me if it seems to be trivial but just to understand regexps: As said here with character (x) :

(x)           matches x and remembers

First part "matches" I can understand but the second part "remembers" is a bit tedious for me to understand. Can someone please help in explaining it in much easier way?

The variable `$1` will contain the value remembered – nu11p01n73R Dec 31 '14 at 15:42 — nu11p01n73R, Dec 31 '14 at 15:42

falsetru · Accepted Answer · 2014-12-31T15:50:06.257

3

It's called capturing group. Using backreference ($1, $2, ...), you can reference it in the substitution string:

'R2D5'.replace(/(\d)/g, '$1$1')
// => "R22D55"

You can also use backreference (\1, \2, ...) in the pattern:

'ABBCCDEF'.match(/(.)\1/g)  // to match consecutive character
// => ["BB", "CC"]

And you will get additional parameters when you use replacement function:

'R2D5'.replace(/(\d)/g, function(fullMatch, capture1) {
    return (parseInt(capture1) + 1).toString();
})
// => "R3D6"

edited Dec 31 '14 at 15:50

answered Dec 31 '14 at 15:43

falsetru

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And when using a function with `replace`, capture groups are the second (and on) arguments: `'R2D5'.replace(/(\d)/g, function(fullMatch, capture1) { ... })` – T.J. Crowder Dec 31 '14 at 15:47
@T.J.Crowder, Thank you for your comment. I updated the answer to mention it. – falsetru Dec 31 '14 at 15:50
@T.J.Crowder Thanks! I did not know this :D – phatskat Dec 31 '14 at 15:50

score 0 · Answer 2 · answered Dec 31 '14 at 15:43

0

In most regex stuff you can specify a "capturing group" and recall them later:

"something".replace(/so(me)/, '$1 ')

Here, the capturing group is (me) - the result will be me thing

answered Dec 31 '14 at 15:43

phatskat

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What does "matches x and remembers the match" means in regexp

2 Answers2