Need explanation of REGEX code

[Howard]

Can someone explain how the REGEX code below works? 

(.)(?![^(]*\))

I know it looks for digits, including two-digit numbers in parentheses, and extracts them and inserts a space after each one, but I do not know how the code starting with (? works.

Here is sample data for it:

010000000

(10)1140006x

002200010

00000(11)01x

311200

Here is output:

0 1 0 0 0 0 0 0 0 

(10) 1 1 4 0 0 0 6 x 

0 0 2 2 0 0 0 1 0 

0 0 0 0 0 (11) 0 1 x 

3 1 1 2 0 0 

[TJ Luoma]

Try pasting it into https://regexr.com

That's what I usually use to translate regex into English :-)

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[jj]

Hi Howard,

Here is a commented version of your regular expression.

(?x)        (?# Allow whitespace and comments.                              )

(           (?# Opening of capture 1.                                       )

    .       (?# Any single character.                                       )

)           (?# Closing of capture  1.                                      )

(?!         (?# Opening negative lookahead assertion.                       )

    [^(]*   (?# Zero or more characters that are not a opening parenthesis. )

    \)      (?# A closing parenthesis.                                      )

)           (?# Closing negative lookahead assertion.                       )

(?!...) is a Negative lookahead assertion.

It basically says: find occurrences of 'this' that are not followed by 'that' but don't include the 'not that' in the match –– hence the 'lookahead'.

For a detailed explanation check the excellent grep documentation in menu Help > BBEdit Help > Grep Reference link.

So that says:

"Any single character that is not followed by zero or more characters that are not the opening parenthesis, followed by a closing parenthesis."

The double negation makes it difficult to fathom.

The negative lookahead assertion says: skip any match that is followed by '...)' where ... are zero of more not '('.

The digits of the first line are not followed by '...)' -> match.

The first character of the second line '(' is followed by '10)' -> skip

The second character of the second line '1' is followed by '0)' -> skip

The third character of the second line '0' is followed by ')' -> skip

The fourth character of the second line ')' is not followed by '...)' -> match

...

A simpler regular expression that will give the same result (and probably be more performant) is:

(\([^\)]*\)|\d)

"Match any parentheses block or any single digits outside of parentheses blocks."

HTH

Jean Jourdain

[jj]

Just seen there are some non digits in your input.

Then use:

(\([^\)]*\)|.)

[Howard]

Thanks. I just tried it for the first time. It is good to know about.

Howard

[Howard]

Thanks Jean for the comprehensive explanation. It is very helpful.