Actually, the ending ? makes the match non-greedy, in detail:
Given:
SASI_Hs01_00205058 HUMAN NM_005762 857 MISSION® siRNA 2
140.00
if (/(SASI\w+)(.+?)\s(\d+)\s/) { print "$3\n"; }
Match starts looking for the literal SASI followed by one or more \w's, which
are upper or lower case letters or digits or underscores, the charcater class:
[a-zA-Z0-9_],
So SASI is followed by letters, underscores or digits till the pattern finds
whitespace, in .+?, '.' is any character except a newline,
plus means one or more characters that are not newlines, the '?' means to
match the minimal pattern/string possible,
the maximal greedy string might grab every character up to the newline
(if there is one) at the end of the line.
The minimal, non-greedy match has to allow the rest of the pattern to match
which is the one or more digits \d+ surronded by white space.
Sincerely,
David Kronheim
Production Support Tier II
Gateway Error Correction, VZ450 EDI, EDI Billing, & Metakey/LIA
484-213-1315
________________________________________
From: Chris Stinemetz [chrisstinem...@gmail.com]
Sent: Thursday, December 29, 2011 2:45 PM
To: Xi Chen
Cc: beginners@perl.org
Subject: Re: Hello a question about ".+?"
On Thu, Dec 29, 2011 at 1:17 PM, Xi Chen <cxde...@gmail.com> wrote:
> Hello everyone,
>
> I have a question about how to translate the meaning of ".+?". Please
> see the examples below:
> SASI_Hs01_00205058 HUMAN NM_005762 857 MISSION® siRNA 2
> 140.00
> I want to get number"857", I found the command below works:
> perl -ne 'if (/(SASI\w+)(.+?)\s(\d+)\s/) { print "$3\n"; }'
> but ".+" or ".*"doesn't work. I don't know why "?" is so important?
>
I believe it makes the grouping optional.
Match 1 or 0 times
HTH,
Chris
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