What is the purpose of [.] in regular expressions?

Question

I found [.] in a regular expression on manpage of notmuch:

notmuch search 'from:"/bob@.*[.]example[.]com/"'

It seemed to be useless because brackets are for list but have only one character, but finally I learned it matches a literal dot.

Then, why they use it rather than \.? Are there any advantages on this expression?

The only thing I can imagine is in contexts where the backslash requires its own escaping, e.g. string literals. — Bergi, Jul 25 '19 at 09:19
`\.` and `[.]` is the same. However, `[.]` is preferable when you do not know escaping rules (how many backslashes to use to escape the dot in some weird environment). `\.` is correct and preferable *regex string*. — Wiktor Stribiżew, Jul 25 '19 at 09:43

score 0 · Accepted Answer · answered Jul 25 '19 at 09:28

At first I thought that this is to avoid double escaping but on further consideration I think this is because a dot in a character set ([]) is treated differently than normal. It makes sense that in a character set a dot only matches a literal dot, the whole point is to match a specific set of characters so having a wildcard in the set doesn't make sense.

So [.,;:] may be used to match punctuation marks.

Once you take that into account it's obvious that [.] just matches dot.

Whether to use \. or [.] is left as an aesthetic decision.

It's not just aesthetic, it's as @WiktorStribiżew commented on the question. — Jani, Aug 02 '19 at 12:50

What is the purpose of [.] in regular expressions?

1 Answers1