Match regex expression Regex sketchengine (doesn't match substring)

user_12176694 0
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I am learning about regular expressions and I'm trying to solve this question: https://regex.sketchengine.co.uk/cgi/ex1.cgi

So far, I've come up with:

^[psr][^ta|?!ea].*$

But instead of checking if it doesn't match 'ea' as a substring, it tries to not match 'e' and 'a' as a second character. What is my error in this?

regex
2 Answers

Your regex is wrong, see its description:

NODE EXPLANATION
^ the beginning of the string
[psr] any character of: 'p', 's', 'r'
[^ta|?!ea] any character except: 't', 'a', '
.* any character except \n (0 or more times (matching the most amount possible))
$ before an optional \n, and the end of the string

Use

.*p[ioa ]t.*

See proof

EXPLANATION

--------------------------------------------------------------------------------
  .*                       any character except \n (0 or more times
                           (matching the most amount possible))
--------------------------------------------------------------------------------
  p                        'p'
--------------------------------------------------------------------------------
  [ioa ]                   any character of: 'i', 'o', 'a', ' '
--------------------------------------------------------------------------------
  t                        't'
--------------------------------------------------------------------------------
  .*                       any character except \n (0 or more times
                           (matching the most amount possible))
user_113298900

In your pattern you do not allow matching pe se and re ruling out respite, but you only don't want to allow pe.

You could use a negative lookahead to rule out a p directly followed by one of your characters in the character class.

^(?!p[tea])[psr].*

The pattern matches:

  • ^ Start of the string
  • (?!p[tea]) Negative lookahead, assert not pt or pe or pa directly to the right
  • [psr].* Match either p s r followed by 0+ times any character

Regex demo

Note that there are no | ? or ! in the example data.

user_54249880
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