Regex for comparison expression

Question

I need to match strings like the following:

( anything >= anything )

and there can by only these comparison operators: >= <= == != < > And they can be there only once. What I have is:

^\(.+(>=|<=|>|<|==|!=).+\)$

But it matches stuff like >=!= and so forth. I did look through the stackoverflow questions and googled but couldn't find the right solution.

Clould you please help me with that?

Answer 1

A regex like ^\(\s*[a-zA-Z0-9_+\-\/* ]+\s*(>=|<=|>|<|==|!=)\s*[a-zA-Z0-9_+\-\/* ]+\s*\)$ should do the trick, right?

A Regex101 with it in action can be found here.

Answer 2

If you are also planning to also capture strings like (myName == "Денис"), you need to use the following regex:

^\((?>(?![<>=]=|!=|[<>]).)*?(?:[<>=]=|!=|[<>])(?>(?![<>=]=|!=|[<>]).)*?\)$

See demo on Regexstorm (supporting .NET regex flavor, unlike regex101.com)

It is much faster than Karthik Manchala's suggestion as per testing results at http://regexhero.net, due to the use of atomic grouping ((?> ... )), character classes ([<>=]), and and lazy matching (*?). Also, in case a space is missing before or after == operator, my regex will still capture the expression.

With (?m)^\((?>(?![<>=]=|!=|[<>]).)*?(?:[<>=]=|!=|[<>])(?>(?![<>=]=|!=|[<>]).)*?\)$ my regex yields 15,783 iterations per second, and Karthik's (?m)^\(((?!(>=|<=|>|<|==|!=)).)+\s+(>=|<=|>|<|==|!=)\s+((?!(>=|<=|>|<|==|!=)).)+\)$ yields 9,204 iterations per second speed.

Answer 3

You can use the following :

^\(((?!(>=|<=|>|<|==|!=)).)+\s+(>=|<=|>|<|==|!=)\s+((?!(>=|<=|>|<|==|!=)).)+\)$

Explanation:

• ((?!(>=|<=|>|<|==|!=)).)+ any character other than (>=|<=|>|<|==|!=)
• \s+(>=|<=|>|<|==|!=)\s+ one of the operators followed by
• ((?!(>=|<=|>|<|==|!=)).)+ any character other than (>=|<=|>|<|==|!=)