如何从Unix / Linux上的文件抓取任意块 [英] How to grab an arbitrary chunk from a file on unix/linux

问题描述

我想一大块从一个二进制文件复制到一个新文件。我已经字节偏移和块长度我要抢。

I'm trying to copy a chunk from one binary file into a new file. I have the byte offset and length of the chunk I want to grab.

我已经使用 DD 工具试过，不过这似乎读取和丢弃数据高达偏移，而不仅仅是追求（我猜是因为dd是复制/变换数据的块）。这使得它很慢（速度较慢的抵消较高这是我试过的命令：

I have tried using the dd utility, but this seems to read and discard the data up to the offset, rather than just seeking (I guess because dd is for copying/converting blocks of data). This makes it quite slow (and slower the higher the offset. This is the command I tried:

dd if=inputfile ibs=1 skip=$offset count=$datalength of=outputfile

我想我可以写一个小的Perl / Python的/不管脚本打开该文件，寻求补偿，那么读写块所需的数据量。

I guess I could write a small perl/python/whatever script to open the file, seek to the offset, then read and write the required amount of data in chunks.

有没有支持这样的一个工具？

Is there a utility that supports something like this?

推荐答案

是的，它是尴尬今天做这与日。我们正在考虑增加skip_bytes和count_bytes PARAMS中的coreutils以帮助DD。以下应工作，虽然：

Yes it's awkward to do this with dd today. We're considering adding skip_bytes and count_bytes params to dd in coreutils to help. The following should work though:

#!/bin/sh

bs=100000
infile=$1
skip=$2
length=$3

(
  dd bs=1 skip=$skip count=0
  dd bs=$bs count=$(($length / $bs))
  dd bs=$(($length % $bs)) count=1
) < "$infile"

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