Re^2: pattern matching

I think liverpole is close, but he's ignoring one important factor: the data contains a space between the data the OP wants to capture, and thus, isn't part of it. So just making the patterns do optional matching, won't cut it.

Here's what I would do:

if (/(\w\w)(?: (\w\w)(?: (\w\w)(?: (\w\w))?)?)?/) {
     # Do something
}
[download]

I don't like the idea of making the parallel items optional, instead, I nest them, so $3 cannot match if $2 didn't match, as both are part of the same optional pattern. Ditto with $4, that can only match if both $3 and $2 matched.

Comment on Re^2: pattern matching Download Code

Replies are listed 'Best First'.
Re^3: pattern matching by vineet2004 (Initiate) on Dec 26, 2006 at 04:38 UTC
thanks guys....	[reply]
Re^3: pattern matching by vineet2004 (Initiate) on Dec 26, 2006 at 07:23 UTC
thanks bart for ur reply ur code is fine....but actually my problem of pattern matching includes 31(or less) instead of the 4(or less) pairs that as i mentioned in my post. i made the change so as to be able to give an example easily. if i follow ur code pattern then it might turn out to be a bit too long......any shorter version??? thanks again for ur help so far vineet	[reply]
Re^4: pattern matching by bart (Canon) on Dec 26, 2006 at 22:47 UTC
Hmm I see what you mean, extending the code with more matches soon gets really unwieldy. You need some kind of looping construct. Now I wish I could say you could handle this easily with a single pattern, but unfortunately, a repetition modifier around captures doesn't produce the desired results: `$_ = 'de ad be ef #junk'; /^(\w\w)(?: (\w\w))/;` [download] will only retain two captures: in the end, $1 will be 'de', the first capture, and $2 will be 'ef', the last one — the rest will simple have been forgotten about. There's no way around it, this requires a two step approach: Step 1) extract the whole of all the captures, Step 2), split it into parts. The first approach is to use split for step 2: `$_ = 'de ad be ef #junk'; /^(\w\w(?: \w\w))/; my @capture = split ' ', $1;` [download] Use //g, either in a loop, or in list context. //g in list context: `$_ = 'de ad be ef #junk'; my @capture = /\G(?:^\|\ )(\w\w)/g;` [download] A loop with //g in scalar context: `$_ = 'de ad be ef #junk'; my @capture; while(/\G(?:^\|\ )(\w\w)/g) { push @capture, $1; }` [download] Be extremely careful with the latter that you don't accidently cause an endless loop. I did, with `/(?:^\|\G\ )(\w\w)/g` [download] I'm still not sure why.	[reply] [d/l] [select]