Add ) at End of Lines Containing ( but Not )

I need help with a regular expression in Notepad++. I want to:

1. Find lines that contain a ( character but do not contain a ) character.
2. Add a ) at the end of those lines.

I tried using this regex to find the lines:

^(?=.*\()(?!.*\)).*$

Then, I used this in the Replace with field to add ) at the end:

\0)

I also tried using $0) and other methods, but it either deletes the line or doesn’t work at all.

for example following is my sample list:

5years

Strta(Nicaragua)

3years

Ismtrtttu(Turkey)

2years

Frrtto(Spain

Lyears

Fulrttsta(Cuba)

0years

Chutrtrtl(UnitedKingdom)

Can someone help me find the correct regex and replacement pattern for this in Notepad++? Thank you!

You don't need any lookarounds, you can make use of a negated character class.

Find what:

^[^\n()]*\(\K[^\n()]*$

The regex matches:

• ^ Start of string
• [^\n()]* Match 0+ times any character except ( ) or a newline
• \( Match (
• \K Forget what is matched so far
• [^\n()]* Match 0+ times any character except ( ) or a newline
• $ End of string

Replace with: the full match followed by a closing parenthesis:

$0\)

See a regex101 demo