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From: "Dave Korn" <dave DOT korn AT artimi DOT com>
To: <cygwin AT cygwin DOT com>
Subject: RE: grep weirdness - matching space character
Date: Tue, 26 Sep 2006 11:39:27 +0100
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On 26 September 2006 11:17, The Blog User wrote:

> I am really struggling to understand what I am doing wrong here.
> 
> I have a log file with a line that looks like this:
> 
> ++ 04:51:32 All 94 items succeeded
> 
> The binary data for that line is this:
> 
> 2B 2B 20 30 34 3A 35 31 3A 33 32 20 41 6C 6C 20 39 34 20 69 74 65 6D 73 20
> 73 75 63 63 65 65 64 65 64 0A
> 
> using grep and tail (versions below) I am failing to match that line
> 
> $ tail -1 /path/to/file/the.log | grep -a "All \d*.items succeeded"

  There's no such thing as \d.
 
> however if I insert 3 (why three?) dots (or a .*) between 'All' and '\d' I
> get a match, what is happening ?

  The dots are eating the '94' as well as the space.

> This seems wrong to me, since - from my knowledge of regex's - that is
> saying there must be three characters between the 'All' and the first
> digit, yet I can see there is only a single space character.

  Escaping a d just matches a literal 'd'.  So the expression '\d*' matches
zero or more of the letter d.  If you use the three dots to eat the two digits
as well as the space, the optional any-number-of-d's is matched by the zero
d's following, and then the trailing 'items succeeded' matches.

  Whereas with only the one dot, the dot matches the space, then there's
zero-optional-'d's, then the '9' fails to match against '.items succeeded'.



    cheers,
      DaveK
-- 
Can't think of a witty .sigline today....


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