Regex matches a string of unique characters

Question

Here is my regex:

((GO)( [AZ])+) 

I want each letter to appear no more than once, unfortunately, it does not work properly, because this input:

 GO ABCC 

returns true, but returns false.

Answer 1

You can use this regex:

 ^(GO(?: ([AZ])(?!.*\2))+)$ 

RegEx Demo

Answer 2

Your regex:

 GO(?:([AZ])(?!.*\1))+$ 

• Corresponds to the letter GO , and then:
• Any AZ character, from zero to infinite time
• the statement for each character encountered that the same character does not match any ( . ) subsequent character before the next line break ( $ ).

The key to this last step, which is all you were missing, is the negative back side of zero length : (?!.*\1)

Answer 3

You can use the following regular expression:

 ^GO (?:([AZ])(?!.*\1)\s*)*$ 

It will correspond to all that:

• starts with GO<space>
• contains only letters ( [AZ] ) which:
  • can be separated by any sequence of blank characters, but:
  • perhaps never seen before.

See working on regex101 !

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Matching examples:

 GO ABC GO ABC GO ABCGO 

Examples of inconsistencies:

 ABC GO AAA