Regex to match for statement

Question

For a university task I need to match for loops from input with regex so I want to write a regex to recognize it.

I tried following regex but it doesn't match anything:

for\((\w*\s+\w+\s*\=\s*\d+\s*)?\;(\s*\w+\s*\W+\d+\s*)\;(\s*\w+\W+)\)\{ . \}

this is the regex I used.

for(int i=1;i<=10;i++){  
System.out.println(i);  
}

and this is something like what I want to match.

In which language are you trying to achieve this? You might better use a parser here. — Jan, Apr 05 '19 at 09:29
Replace `\{ . \}` with `\{[\S\s]+\}`. However, be aware that this won't match any kind of a for loop. — 41686d6564 stands w. Palestine, Apr 05 '19 at 09:32
Please don't use a regex to parse a complex language such as Java, especially when tons of parsers already exist for the language. — Aaron, Apr 05 '19 at 09:34
@AhmedAbdelhameed tank you very much. this is a university task and I should implement it with regex. I think it is better to send your comment as an answer so I can accept it. — Amir Sasani, Apr 05 '19 at 17:23

score 1 · Accepted Answer · answered Apr 05 '19 at 19:53

As others have suggested, this is not a suitable task for regex; you should use a parser.

That being said, if you must use regex and you only care about matching a for loop in the exact format you provided, you may replace the \{ . \} part with something like \{[\S\s]+\} in order to match the body successfully.

Here's the full pattern:

for\s*\((\w*\s+\w+\s*\=\s*\d+\s*)?\;(\s*\w+\s*\W+\d+\s*)?\;(\s*\w+\W+)?\)\s*\{[\S\s]+?\}

Regex101 demo.

I made some additional changes to it. For example, allowed more whitespaces where appropriate and made the 2nd and 3rd groups optional, since each of the initialization, the condition and the update (increment/decrement) are indeed optional in Java and to match an infinite loop as well. Feel free to keep or disregard these changes based on your requirements.

However, as I said above, this focuses only on the format of the for loop provided in the question and it will not match every possible way to write a for loop as I previously mentioned in the comments. Some examples of those cases:

// The update/increment may use a different operator.
for (int i = 1; i <= 10; i += 1) { }

// The condition can be any expression that evaluates to boolean.
for (int i = 1; i * 2 <= 10; i++) { }

// A for loop can have no braces.
for (int i = 1; i <= 10; i++)           
    System.out.println(i);

// Etc.

Regex to match for statement

1 Answers1