使用正则表达式提取值

Question

Say I have this string: fg_^"-kv:("value_i_want")frt . That string will stay constant except for value_i_want - which could change all the time. This little string is hidden within a huge string of data (constantly changing), I have saved in a PHP variable

Is there any I could do a Regular Expression on a string, let's say of 50000 characters to find that string (above) without knowing what the value_i_want is, and then saving the value in a variable - using PHP

Answer 1

You can just use strpos to find where the value you want is. You may need to tweak this a little, I haven't tested it. $long_string is the string you are searching for a match in.

$start = strpos($long_string, 'fg_^"-kv:("', 0);
$end = strpos($long_string, '")frt', $start);
$value_i_want = substr($long_string, $start+11, $end-$start-11);

Answer 2

Try this:

if (preg_match_all('/(?<=fg_\^\"\-kv:\(\")[a-z_]+(?=\"\)frt)/', $yourstring, $matches)) {
  echo "Match was found <br />";
  echo $matches[0];
}

Pattern: (?<=fg_\\^\\"\\-kv:\\(\\")[a-z_]+(?=\\"\\)frt)

(?<=fg_\\^\\"\\-kv:\\(\\") - positive lookbehind assertion, means that searched string should be after exactly this string: fg_^"-kv:("

(?=\\"\\)frt) - positive lookahead assertion, means the same, but before: ")frt

[a-z_]+ - the string you are looking for, may consist of one or more letter and underscores. Change it for your needs.

Demo: https://regex101.com/r/vS7dI0/1