Question

Conditions updated

There is often a situation where you want to extract a substring upto (immediately before) certain characters. For example, suppose you have a text that:

• Does not start with a semicolon or a period,
• Contains several sentences,
• Does not contain any “\n”, and
• Ends with a period,

and you want to extract the sequence from the start upto the closest semicolon or period. Two strategies come to mind:

1. /[^;.]*/
2. /.*?[;.]/

I do either of these quite randomly, with slight preference to the second strategy, and also see both ways in other people’s code. Which is the better way? Is there a clear reason to prefer one over the other, or are there better ways? I personally feel, efficiency aside, that negating something (as with [^]) is conceptually more complex than not doing it. But efficiency may also be a good reason to chose one over the other.

Answer 1

I came up with my answer. The two regexes in my question were actually not expressing the same thing. And the better approach depends on what you want.

1. If you want a match up to and including a certain character, then using

   /.*?[;.]/

is simpler.

1. If you want a match up to right before (excluding) a certain character, then you should use:

   /[^;.]*/