Regex to match a string that contains substrings separated with dots

I need to get a value from an array using the dot notation. For example:

$arr = [
    'first' => [
        'second' => [
            'third' => 'hello'
        ]
    ]
];

$value = array_dot($arr, 'first.second.third'); // returns "hello"

So what I need to do is check if it’s a valid string by which we could get a value from array.

Constraints:

• non-whitespace characters only
• contains at least one dot
• cannot start or end with a dot
• every dot must have a non-dot substring before and after it

Cases:

`value.inside.array` valid
`val-2.of.array` valid
`.var2.in.arr` invalid
`dot.notation.` invalid
`value. dot` invalid
`consecutive....dots` invalid

Answer

Try this:

^[^.s]S*.S*[^.s]$

Explanation:

^[^.s]     Start with any non-dot and non-white character
S*             Any non space characters
.              Force at least one dot
S*             Any non space characters
[^.s]$    End with any non-dot and non-white character

Demo here.