Regular expression to find number in parentheses, but only at beginning of string

Question

Disclaimer: I'm new to writing regular expressions, so the only problem may be my lack of experience.

I'm trying to write a regular expression that will find numbers inside of parentheses, and I want both the numbers and the parentheses to be included in the selection. However, I only want it to match if it's at the beginning of a string. So in the text below, I would want it to get (10), but not (2) or (Figure 50).

(10) Joystick Switch - Contains control switches (Figure 50)
Two (2) heavy lifting straps

So far, I have (\(\d+\)) which gets (10) but also (2). I know ^ is supposed to match the beginning of a string (or line), but I haven't been able to get it to work. I've looked at a lot of similar questions, both here and on other sites, but have only found parts of solutions (finding things inside of parentheses, finding just numbers at the beginning for a string, etc.) and haven't quite been able to put them together to work.

I'm using this to create a filter in a CAT tool (for those of you in translation) which means that there's no other coding languages involved; essentially, I've been using RegExr to test all of the other expressions I've written, and that's worked fine.

Answer 1

The regex should be

^\(\d+\)

• ^ Anchors the regex at the start of the string.

• \( Matches (. Should be escaped as it has got special meaning in regex

• \d+ Matches one or more digits

• \) Matches the )

• Capturing brackets like (\(\d+\)) are not necessary as there are no other characters matched from the pattern. It is required only when you require to extract parts from a matched pattern

  For example if you like to match (50) but to extract digits, 50 from the pattern then you can use

  \((\d+)\)
  

  here the \d+ part comes within the captured group 1, That is the captured group 1 will be 50 where as the entire string matched is (50)

Regex Demo

Answer 2

Like so:

^\(\d+\)

^ anchor

Each of ( and ) are regex meta character, so they need to be escaped with \

So \( and \) match literal parenthesis.

( and ) captures.

\d+ match 1 or more digits

Demo