Delete the first 20k from 76k file

dave043 · #1 (**permalink**) 02-28-2007

I'm a bit new at unix yet but I'm trying to write a script that will help me to delete the first 20k from a 76k file. So the end result will be a 56k file. I'm using sh. Please help

D

radoulov · #2 (**permalink**) 02-28-2007

Code:

$ du -k f
76      f
$ dd if=f of=f_ bs=1k skip=20
56+0 records in
56+0 records out
$ du -k f_
56      f_

dave043 · #3 (**permalink**) 02-28-2007

maybe I said this wrong on my post. I need to delete the FIRST 20k (size) from a file (lets say I don't know the file size) and the name of the file is test.log. How do go about deleting the first 20k from a file size that I do not know.

D

sb008 · #4 (**permalink**) 02-28-2007

Quote:

Originally Posted by dave043

maybe I said this wrong on my post. I need to delete the FIRST 20k (size) from a file (lets say I don't know the file size) and the name of the file is test.log. How do go about deleting the first 20k from a file size that I do not know.

D

radoulov gave you the correct answer.

The block size is defined in k.
It says to skip the first 20 blocks, so 20 k.
The rest (all after the first 20k) is copied.

dave043 · #5 (**permalink**) 02-28-2007

can I run this in a shell script? if so how do I do this?

D

sb008 · #6 (**permalink**) 02-28-2007

Quote:

Originally Posted by dave043

can I run this in a shell script? if so how do I do this?

D

Depends on what you exactly want, you could make a script with 1 or 2 arguments.

With 1 argument you can specify the name of the file from which you want to cut of the first 20k, the new file will have the same name with ".new" added.

Code:

#!/usr/bin/ksh

dd if=${1} of=${1}.new bs=1k skip=20

Suppose we name this script "cut20k-v1.sh"
You would run it like "./cut20k-v1.sh <file>"

E.g.

Code:

./cut20k-v1.sh testfile

It would cut the first 20k from the file "testfile" and the resullt would be in the file "testfile.new"

You could create a script which takes 2 arguments. The first argument would be the name of the file from which you would like to cut off the first 20k and the second argument would be the name of the file with the first 20k missing.

Code:

#!/usr/bin/ksh

dd if=${1} of=${2} bs=1k skip=20

Suppose we name this script "cut20k-v2.sh"
You would run it like "./cut20k-v2.sh <infile> <outfile>"

E.g.

Code:

./cut20k-v2.sh testfile resultfile

It would cut the first 20k from the file "testfile" and the resullt would be in the file "tesiultfile"

jankar · #7 (**permalink**) 02-13-2008

I am new to scripting and am trying to do a similar thing;

I would like to take the first 20k out of a file, leave the rest of the file intact then output that 20k to a new file.

I am not sure how to do this.. Thanks for the help!

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