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dd skip_bytes=x count_bytes=x
From: |
Pádraig Brady |
Subject: |
dd skip_bytes=x count_bytes=x |
Date: |
Wed, 07 Oct 2009 12:12:17 +0100 |
User-agent: |
Thunderbird 2.0.0.6 (X11/20071008) |
Pádraig Brady wrote:
> On 16th June 2008, Paul Eggert wrote:
>> Pádraig Brady <address@hidden> writes:
>>
>>> 5. I think it would be nice for dd to support reading portions of
>>> a file efficiently. As far as I can see it can only do it by reading
>>> 1 byte at a time. Perhaps skip_bytes=x and count_bytes=x would
>>> be useful additions?
>> These also sound like good suggestions.
>
> I just noticed in the info docs for dd that there
> is a method to achieve skip_bytes at least:
>
> (dd bs=1 skip=123456 count=0 && dd bs=8192) < file
For my reference one could also efficiently
achieve count_bytes using the following:
bs=8192
skip_bytes=$1
count_bytes=$2
(
dd bs=1 skip=$skip_bytes count=0
dd bs=$bs count=$(($count_bytes / $bs))
dd bs=$(($count_bytes % $bs)) count=1
) < file
Still, supporting those internal to dd would
be simpler, more portable and robust.
cheers,
Pádraig.
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