Exact string coldfusion regular expression

Question

I am using a regular expression to replace all characters that are not equal to the exact word "NULL" and also keep all digits. I did a first step, by replacing all "NULL" words from my string with this :

<cfset data = ReReplaceNoCase("123NjyfjUghfLL|NULL|NULL|NULL","\bNULL\b","","ALL")>

It removes all instances of the exact "NULL" word, that means it does not remove letters "N", "U" and "L" from the substring "123NjyfjUghfLL". And this is correct. But now, I want to reverse that. I want to keep only "NULL" word, meaning that it removes single "L", "U" and "L". So I tried that :

<cfset data = ReReplaceNoCase("123NjyfjUghfLL|NULL|NULL|NULL","[^\bNULL\b]","","ALL")>

But now this keeps all "N", "U" and "L" letters, so it outputs "NULLNULLNULLNULL". There should be only 3 times "NULL".

Can someone help me with this please? And where to add the extra code to keep digits? Thank you.

I've come up with this: `writeOutput(RereplaceNoCase(variables.a,"^((?!NULL).)*","","ALL"));` based on http://stackoverflow.com/questions/406230/regular-expression-to-match-text-that-doesnt-contain-a-word but it's still not quite what you want. a good starting point perhaps @adamcameron can suggest something. — Jarede, Apr 30 '15 at 23:20

Regular Jo · Accepted Answer · 2015-05-01T20:42:58.470

You can do this

<cfset data = ReReplaceNoCase("123NjyfjUghfLL|NULL|NULL|NULL","(^|\|)(?!NULL(?:$|\|))([^|]*)(?=$|\|)","\1","ALL")>

(^|\|)(?!NULL(?:$|\|))([^|]*)(?=$|\|)

Explanation:

 (                   # Opens Capture Group 1
     ^               # Anchors to the beginning to the string.
 |                   # Alternation (CG1)
     \|              # Literal |
 )                   # Closes CG1
 (?!                 # Opens Negative Lookahead
     NULL            # Literal NULL
     (?:             # Opens Non-Capturing group
         $           # Anchors to the end to the string.
     |               # Alternation (NCG)
         \|          # Literal |
     )               # Closes NCG
 )                   # Closes NLA
 (                   # Opens Capture Group 2
     [^|]*           # Negated Character class (excludes the characters within)
                       # None of: |
                       # * repeats zero or more times
 )                   # Closes CG2
 (?=                 # Opens LA
     $               # Anchors to the end to the string.
 |                   # Alternation (LA)
     \|              # Literal |
 )                   # Closes LA

Regex101.com demo

Lastly, some insight about character classes (content between square brackets)

What [^\bNULL\b] means is

 [^\bNULL\b]     # Negated Character class (excludes the characters within)
                   # None of: \b,N,U,L
                   # When \b is inside a character class, it matches a backspace character.
                   # Outside of a character class, \b matches a word boundary as you use it in your first code.

Character classes are not designed for matching or ignoring words, they're designed for permitting or excluding characters or ranges of characters.

Edit:

Ok so it works well. But what if I would like to keep also the digits? I am a kind of lost in this line of code and I cannot find where to put extra code... I think the extra code would be [^0-9] right?

This regex (demo) works to also permit numbers of any length where the number is the entire value

(^|\|)(?!(?:NULL|[0-9]+)(?:$|\|))([^|]*)(?=$|\|)

You can also use this regex (demo) to permit numbers with a decimal value.

(^|\|)(?!(?:NULL|[0-9]+(?:\.[0-9]+)?)(?:$|\|))([^|]*)(?=$|\|)

Ok so it works well. But what if I would like to keep also the digits? I am a kind of lost in this line of code and I cannot find where to put extra code... I think the extra code would be `[^0-9]` right? — J-P-Dude, May 01 '15 at 19:55
Edit your original question with examples, but this might be what you want `(^|\|)(?!(?:NULL|[0-9]+)(?:$|\|))([^|]*)(?=$|\|)`. — Regular Jo, May 01 '15 at 20:10
Unfortunately, it does not work for me, it output the same result as the first answer given. — J-P-Dude, May 01 '15 at 20:20
@J-P-Dude I meant to add examples, but I posted some possible regexes as an edit, with examples. I hope it helps you. — Regular Jo, May 01 '15 at 20:44

Exact string coldfusion regular expression

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