Regex find word in the string

Question

In general terms I want to find in the string some substring but only if it is contained there.

I had expression :

^.*(\\bpass\\b)?.*$

Answer 1

You're just missing a bit for it to work (plus that ? is at the wrong position).

If you want to match the frist occurance: ^(.*?)(\bpass\b)(.*)$. If you want to match the last occurance: ^(.*)(\bpass\b)(.*?)$.

This will result in 3 capture groups: Everything before, the exact match and everything following.

. will match (depending on your settings almost) anything, but only a single character. ? will make the preceding element optional, i.e. appearing not at all or exactly once. * will match the preceding element multiple times, i.e. not at all or an unlimited amount of times. This will match as many characters as possible. If you combine both to *? you'll get a ungreedy match, essentially matching as few characters as possible (down to 0).

Edit: As I read you only want pass and the complete string, depending on your implementation/language, the following should be enough: ^.*(\bpass\b).*?$ (again, the ungreedy match might be swapped with the greedy one). You'll get the whole expression/match as group 0 and the first defined match as group 1.

Answer 2

A period only matches a single character, so you're

^.(\bpass\b)?.$

is matching:

• Start of input
• A single character
• Optionally
  • Word boundary
  • "pass"
  • Word boundary
• Single char
• End of input

which I would not expect to match "high pass h3" at all.

The regular expression:

pass

(no metacharacters) will match any string containing "pass" (but then so would a "find string in string" function, and this would probably be quicker without the complexities of a regex).

Answer 3

Use this one:

^(.*?(\bpass\b)[^$]*)$

1. First capture for the entire line.
2. Second capture for the expected word.

Check the demo.

More explanation:

          ┌ first capture
          |
 ⧽------------------⧼
^(.*?(\bpass\b)[^$]*)$
  ⧽-⧼          ⧽---⧼
   | ⧽--------⧼  |
   |     |       └ all characters who are not the end of the string
   |     |
   |     └ second capture
   |
   └ optional begin characters