Regular Expressions 101

Explanation

Pro

Negative Lookbehind(?<!\d)

\da Unicode decimal digit

Group 1(($)?\d+(?:[.-]\d+)?(?(2)$))

Group 2(\()?

?repeats the group contents below at most once:

\(the literal ( (40₁₀ / 50₈ / 28₁₆)

\d+a Unicode decimal digit, repeated at least once

Non-Capturing Group(?:[.-]\d+)?

?repeats the group contents below at most once:

Character Class[.-]

.the literal . (46₁₀ / 56₈ / 2E₁₆)

-the literal - (45₁₀ / 55₈ / 2D₁₆)

\d+a Unicode decimal digit, repeated at least once

Condition(?(2)\))

Uses the first branch if group 2 matched

If the condition is true, match this branch:\)

\)the literal ) (41₁₀ / 51₈ / 29₁₆)

\*the literal * (42₁₀ / 52₈ / 2A₁₆)

\1the text saved by group 1

Negative Lookahead(?!\d)

\da Unicode decimal digit

Global pattern flags

g modifier: global. Finds all matches instead of stopping after the first

m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string

Detailed match information will be displayed here automatically.

25 tokens

(?<!\d)((\()?\d+(?:[.-]\d+)?(?(2)\)))\*\1(?!\d)

New

5*5 --> 5  
3.14*4 --> no return  
(10-4)*(10-4) --> (10-4)
5.3*5.3
44*444

5*5 --> 5  
3.14*4 --> no return  
(10-4)*(10-4) --> (10-4)
5.3*5.3
44*444