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Re: GNU grep 2.5.1

From: Claudio Fontana
Subject: Re: GNU grep 2.5.1
Date: Fri, 1 Apr 2005 22:56:41 +0200 (CEST)


the correct place to speak about supposed grep bugs is
now address@hidden .

By the way, I think that Marvin is trying to avoid
using od and going directly for the bytes when he

> I have been doing
> od -x bigDataFile | grep -c "aa55 0000 0490"
> which gives me the answer 560912 when a file has not
> been
> corrupted. This is fine but quite slow.
> Today I decided that
> grep -c "\xaa\x55\x00\x00\x04\x90" bigDataFile
> should be faster.

The main problem is that the \xnn syntax is not a
posix regex, but a perl regex.

There is another (byte ordering) problem in the fact
that od -x shows bytes in pairs, interpreting them as
short integers.

I think the original poster would solve his problem

1) using 

$ od -t x1 BigDataFile

to extract the correct byte by byte sequence he wants
to use as validation

2) replacing 

grep -c "\xNN\xNN\xNN"


grep -P -c '\xNN\xNN\xNN'

This being said, there are lots of better solutions to
the 'validation' problem that do not involve grep.

Hope this helps.


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