Regex string doesn't contain 2 dots in a row

Question

I'd like to know if this regex expression is correct for checking that a string doesn't start with a dot, doesn't end with a dot and contains at least one dot anywhere but not the start or end:

My issue is that I can't figure on how to check if there's 2 dots in a row.

/^([^.])+([.])+.*([^.])$/

which programming language do you use? there could be easier solution.. — Kent
– Kent, Commented Dec 15, 2016 at 12:38
"I'd like to know if this regex expression is correct" -- there is only one way to know if it is correct or not (given that you didn't mention the program or language you want to use it with): pass it to the target program and see if it does what you want. — axiac
– axiac, Commented Dec 15, 2016 at 12:38
I'm using PHP sorry! But I want to know how to make so a string cannot have 2 dots in a row, so for example "test..test" wouldn't be acceptable but test.test would be acceptable. — tempestor
– tempestor, Commented Dec 15, 2016 at 13:29
@tempestor: See my answer for a solution that works exactly as you need. Use if (preg_match('~^[^.]+(?:\.[^.]+)+$~', $s, $matches)) { /* VALID! */ }. The 3rd $matches argument is actually not necessary. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Dec 15, 2016 at 13:35

Wiktor Stribiżew · Accepted Answer · 2016-12-15 12:38:24Z

4

It seems you need to use

^[^.]+(?:\.[^.]+)+$

See the regex demo

Details:

^ - start of string
[^.]+ - 1+ chars other than a . (so, the first char cannot be .)
(?:\.[^.]+)+ - 1 or more (thus, the dot inside a string is obligatory to appear at least once) sequences of:
- \. - a dot
- [^.]+ - 1+ chars other than . (the + quantifier makes a char other than . appear at least once after a dot, thus, making it impossible to match the string with 2 dots on end)
$ - end of string.

answered Dec 15, 2016 at 12:38

Wiktor Stribiżew

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3 Comments

user3012759 Over a year ago

would ^[^.]+(?:\.{0,x}[^.]+)+$ that not fix the 'must have .' problem? where x is max consecutive dots?

Wiktor Stribiżew Over a year ago

@user3012759: the limiting quantifier is redundant here because we need to match . once between 2 non-. symbols.

user3012759 Over a year ago

Ah, yes you're right OP asked about at least one, so yes your solution is perfectly fine.

Toto · Accepted Answer · 2016-12-15 12:44:03Z

2

You're close, have a try with:

^[^.]+(?:\.[^.]+){2,}$

It maches strings that have 2 or more dot, but not at the begining or at the end.

If you want one or more dot:

^[^.]+(?:\.[^.]+)+$

If you want one or two dots:

^[^.]+(?:\.[^.]+){1,2}$

edited Dec 15, 2016 at 12:44

answered Dec 15, 2016 at 12:38

Toto

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