Regex - At least one occurence of 'F' in a 14 character string but not at 7th position

user_18080670 0
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I have to check many strings which are 14 characters long. There should be at least one occurrence of 'F' in a 14 character string but not at 7th position.

Currently, I'm doing this in 2 steps.

First, check if 'F' is not present at position 7 and save them.

^.{6}[^F].{7}$

Then check if there is at least one occurrence of 'F' in the saved strings.

^[F]+$

Is there a better way to do this?

regex
2 Answers

If supported, you can make use of lookarounds asserting an F and not match it on the 7th position:

^(?=[^F\n]*F)(?:.{6}[^F].{7})$

Regex demo

user_54249880

Just as an alternative:

^(?!.{6}F|[^F]+$).{14}$

See an online demo

  • ^ - Start-line anchor;
  • (?!.{6}F|[^F]+$) - Negative lookahead with alternation to avoid a line with an 'F' at index 7 or a line with no 'F' at all;
  • .{14}$ - 14 Characters other than newline upto end-line anchor.
user_97581940
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