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jsosic
Guru
Joined: 02 Aug 2004
Posts: 510
Location: Split (Croatia)
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 Posted: Thu Jan 29, 2009 10:12 pm Post subject: edit file with dd ?!?! |
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Hi guys!
How to just edit portion of file with a 'dd' command? I mean, look at this: | Code: | % dd if=/dev/urandom of=file bs=512 count=10240
% ls -alh file
-rw-r--r-- 1 jsosic users 5.0M 2009-01-29 23:06 file
% dd if=/dev/urandom of=file bs=512 count=1024 seek=1024
1024+0 records in
1024+0 records out
524288 bytes (524 kB) copied, 0.309451 s, 1.7 MB/s
% ls -alh file
-rw-r--r-- 1 jsosic users 1.0M 2009-01-29 23:06 file |
Why is dd simply overwriting file? I know it operates on raw data, but how can I trick it into overwriting just a part of my file...
_________________
I avenge with darkness, the blood is the life
The Order of the Dragon, I feed on human life |
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Akkara
Bodhisattva
Joined: 28 Mar 2006
Posts: 6702
Location: &akkara
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| Posted: Thu Jan 29, 2009 11:14 pm Post subject: |
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You need to use the conv=notrunc option (see man dd).
Note that for that to work, dd itself must open the output file, using of=..., as you have done. Shell I/O redirection woun't work since the shell opens those files. |
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paulbiz
Guru
Joined: 01 Feb 2004
Posts: 508
Location: St. Louis, Missouri, USA
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| Posted: Thu Jan 29, 2009 11:21 pm Post subject: |
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try "conv=notrunc"
edit: you beat me  I had reply typed before you, but then someone came to me and had a conversation before i clicked "submit"  |
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jsosic
Guru
Joined: 02 Aug 2004
Posts: 510
Location: Split (Croatia)
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| Posted: Thu Jan 29, 2009 11:30 pm Post subject: |
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Thanks to you both!
_________________
I avenge with darkness, the blood is the life
The Order of the Dragon, I feed on human life |
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