trying to understand capture groups/repetition (regex)

[Marcio Humpris <ma...@gmail.com>]

Can someone kindly explain a regex?

Lose .{0,2}.{0,1}(KG|Quilos|Kilos|Pounds|Lb)

It matches fine lose 22 pounds, lose 5 pounds. Now 3 digits such as lose
100 pounds it doesnt which is ok.

I was trying to understand those capture groups .{0,2}.{0,1}

. is any character and the 0,2 seems to be repetitions, but i really dont
understand it.

Thanks

Re: trying to understand capture groups/repetition (regex)

[John Hardin <jh...@impsec.org>]

On Thu, 31 Oct 2013, Marcio Humpris wrote:

> Can someone kindly explain a regex?
>
> Lose .{0,2}.{0,1}(KG|Quilos|Kilos|Pounds|Lb)
>
> It matches fine lose 22 pounds, lose 5 pounds. Now 3 digits such as lose
> 100 pounds it doesnt which is ok.
>
> I was trying to understand those capture groups .{0,2}.{0,1}
>
> . is any character and the 0,2 seems to be repetitions, but i really dont
> understand it.

{0,2} means "from zero to 2 repetitions".

Three digits should match that RE because it matches up to three of 
anything before the explicit text. However, if it was three digits *plus a 
space* it would not match because the space has to be matched too - 
that's *four* characters there.

That's an ugly and inefficient RE. If you're trying to match an optional 
number there, here's a much better way to do it:

 	/Lose (?:\d+\s)?(?:KG|Quilos|Kilos|Pounds|Lb)/

Breakdown:
 	"Lose ", followed by
 	(one or more digits followed by a space) maybe?, followed by
 	(one of the specified strings)


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