Question

I work in an environment where I am only allowed to use Regex for string manipulation, and I need to consume a string from start until a certain keyword appears in that string. But sometimes that keyword might not appear at all – the regex needs to take this into account, meaning the keyword appearance is optional and if it doesn’t appear I want to consume the full string to the end.

The keyword is dontconsumeafterthis

Example with the keyword:

this is a string containing the keyword dontconsumeafterthis this part
should not be consumed

Required output:

this is a string containing the keyword

Example without the keyword:

this is another string without the keyword whatever etc. pp.

Required output:

this is another string without the keyword whatever etc. pp.

Answer 1

The following regex should solve it (works for me in Expresso):

(.*?)(?=dontconsumeafterthis)|(.*)

Explanation: There are 2 options, the last one takes the entire string if the first does not match, but the first matches only if it hits dontconsumeafterthis and then excludes that from the capture by using the ?= operator – also, please note the *? (lazy evaluation), which takes multiple occurrences of the dontconsumeafterthis into account).