Perl Regular expression | how to exclude words from a file

Question

i searching to find some Perl Regular Expression Syntax about some requirements i have in a project. First i want to exclude strings from a txt file (dictionary).

For ex

Answer 1

To not match a word from a file you might check whether a string contains a substring or use a negative lookahead and an alternation:

^(?!.*(?:tree|car|ship)).*$

• ^ Assert start of string
• (?! negative lookahead, assert what is on the right is not
  • .*(?:tree|car|ship) Match 0+ times any char except a newline and match either tree car or ship
• ) Close negative lookahead
• .* Match any char except a newline
• $ Assert end of string

Regex demo

To not allow a string to have over 3 times a char repeat you could use:

\b(?!(?:\w*(\w)\1){3})\w+\b

• \b Word boundary
• (?! Negative lookahead, assert what is on the right is not
  • (?: NOn capturing group
  • \w*(\w)\1 Match 0+ times a word character followed by capturing a word char in a group followed by a backreference using \1 to that group
  • ){3} Close non capturing group and repeat 3 times
• ) close negative lookahead
• \w+ Match 1+ word characters
• \b word boundary

Regex demo

Update

According to this posted answer (which you might add to the question instead) you have 2 patterns that you want to combine but it does not work:

(?=^(?!(?:\w*(.)\1){3}).+$)(?=^(?:(.)(?!(?:.*?\1){4}))*$)

In those 2 patterns you use 2 capturing groups, so the second pattern has to point to the second capturing group \2.

(?=^(?!(?:\w*(.)\1){3}).+$)(?=^(?:(.)(?!(?:.*?\2){4}))*$)
                                               ^  

Pattern demo