Do I need to escape dash character in regex?

Question

I'm trying to understand dash character - needs to escape using backslash in regex?

Consider this:

var url     = '/user/1234-username';
var pattern = /\/(\d+)\-/;
var match   = pattern.exec(url);
var id      = match[1]; // 1234

As you see in the above regex, I'm trying to extract the number of id from the url. Also I escaped - character in my regex using backslash \. But when I remove that backslash, still all fine ....! In other word, both of these are fine:

Now I want to know, which one is correct (standard)? Do I need to escape dash character in regex?

I think that you only need to escape the dash when it is inside the `[]` not sure though. — Jorge Campos, Feb 21 '16 at 13:17
@jonrsharpe What do you mean exactly? If I know the answer, then why should I ask it? — Shafizadeh, Feb 21 '16 at 13:20
That's a good question! So why *have* you asked it, given that you've already demonstrated to yourself that you *don't* need to escape that dash? — jonrsharpe, Feb 21 '16 at 13:20
@JorgeCampos and even then, only when it's not the first or last character (eg. `[a-z0-9_-]` allows alphanumeric, underscore and hyphen) — Niet the Dark Absol, Feb 21 '16 at 13:21

score 58 · Accepted Answer · answered Feb 21 '16 at 13:21

You only need to escape the dash character if it could otherwise be interpreted as a range indicator (which can be the case inside a character class).

/-/        # matches "-"
/[a-z]/    # matches any letter in the range between ASCII a and ASCII z
/[a\-z]/   # matches "a", "-" or "z"
/[a-]/     # matches "a" or "-"
/[-z]/     # matches "-" or "z"

score 11 · Answer 2 · edited Jul 31 '22 at 20:34

11

- may have a meaning only inside a character class [], so when you're outside of it you don't need to escape -

edited Jul 31 '22 at 20:34

Nas Banov

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answered Feb 21 '16 at 13:21

Gavriel

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Do I need to escape dash character in regex?

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