get a part of a binary file using gnu-coreutils, bash

Question

I want to get a part of a binary file, from byte #480161397 to #480170447 (included, 9051 bytes in total)

I use cut -b, and I expected the size of trunk1.gz to be 9051 bytes, but I get a different result.

$ wget https://commoncrawl.s3.amazonaws.com/crawl-data/CC-MAIN-2016-07/segments/1454701152097.59/warc/CC-MAIN-20160205193912-00264-ip-10-236-182-209.ec2.internal.warc.gz

$ cut -b480161397-480170447 CC-MAIN-20160205193912-00264-ip-10-236-182-209.ec2.internal.warc.gz >trunk1.gz

$ echo $((480170447-480161397+1))
9051

$ ls -l trunk1.gz
-rw-r--r--  1 david  staff     3400324 Sep  8 10:28 trunk1.gz

What is wrong?

That means your cut is not doing what you thought it should. I tried cut -b with some .gz files that I had as well. I also got file sizes larger than the bbytes specified. In normal files this can be explained by the fact that there are columns in the files. So the command cut -b picks out the corresponding bytes from each line. Hence large file sizes. i.e. cut -b is probably not what you need here. — Chem-man17
– Chem-man17, Commented Sep 8, 2016 at 8:57

Leon · Accepted Answer · 2016-09-08 08:54:50Z

2

cut -bN-M copies the range N-M bytes from every line of the input.

Example:

$ cut -b4-7 <<END
0123456789
abcdefghij
ABCDEFGHIJ
END

Output:

3456
defg
DEFG

Consider using dd for your purposes.

answered Sep 8, 2016 at 8:54

Leon

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oliv · Accepted Answer · 2016-09-08 08:56:00Z

1

If you work with binary, I advise you to use dd command.

dd if=trunk1.gz bs=1 skip=480161397 count=9051 of=output.bin

bs is the block size and is set to 1 byte.

answered Sep 8, 2016 at 8:56

oliv

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1 Comment

David Portabella Over a year ago

dd if=CC-MAIN-20160205193912-00264-ip-10-236-182-209.ec2.internal.warc.gz bs=1 skip=$((480161397-1)) count=9051 of=trunk1.gz

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