How to write regex to extract a string delimited by two periods even if the first periods is not pre-CodePudding

I'm trying to write a regex to extract a string delimited by two periods even if the first period is not present.

Example 1:
Source string: fwe4d.tobe-extracted.s4red
Output string: tobe-extracted

Example 2:
Source string: tobe-extracted.s4red
Output string: tobe-extracted

I wrote the following regex but it only works if two periods are present.

$pattern = "/\.([^\.] )\./";

CodePudding user response：

You can use a capture group and an anchor:

^(?:[^\s.] \.)?([^\s.] )\.

Explanation

^ Start of string
(?:[^\s.] \.)? Optionally match 1 non whitespace chars without a dot, and then match .
([^\s.] ) Capture group 1, match 1 non whitespace chars or a dot
\. Match the second dot

Regex demo