Regular expressions: find string without substring

Question

I have a big text:

\"Big piece of text. This sentence includes \'regexp\' word. And this
sentence doesn\'t include that word\"

I need to fi

Answer 1

Use lookahead asseterions.

When you want to check if a string does not contain another substring, you can write:

/^(?!.*substring)/

You must check also the beginning and the end of line for this and word:

/^this(?!.*substring).*word$/

Another problem here is that you don't work find strings, you want find sentences (if I understand your task right).

So the solution looks like this:

perl -e '
  local $/;
  $_=<>;
  while($_ =~ /(.*?[.])/g) { 
    $s=$1;
    print $s if $s =~ /^this(?!.*substring).*word[.]$/
  };'

Example of usage:

$ cat 1.pl
local $/;
$_=<>;
while($_ =~ /(.*?[.])/g) {
    $s=$1;
    print $s if $s =~ /^\s*this(?!.*regexp).*word[.]/i;
};

$ cat 1.txt
This sentence has the "regexp" word. This sentence doesn't have the word. This sentence does have the "regexp" word again.

$ cat 1.txt | perl 1.pl 
 This sentence doesn't have the word.