How regex match exact 3 numbers

Question

I want true for these cases:

.123
.000
.999

And want false for these cases:

123
a123
.123a
.1234
a.123

This is my current regex:

match, _ := regexp.MatchString("[.]{1}[0-9]{3}", ".123a")
fmt.Println(match)

But this pattern doesn't return false for:

.123a
.1234
a.123

What is the correct regex?

Answer 1

The pattern is as simple as:

^\.\d{3}$

Same as:

^\.[0-9]{3}$

Which is:

^     // from the beginning
\.    // a single dot
\d{3} // a digit (exactly 3 times)
$     // until the end of the string

You have to escape the \ symbol though so: ^\\.\\d{3}$

Regexp Demo. Go Demo.

Answer 2

You are close, try restricting the match with ^[.]{1}[0-9]{3}$

See online demo