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Sed command to replace 3rd and 4th instance in a file

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dynacade
 PostPosted: Fri Nov 11, 2011 2:55 pm   

Joined: Tue Jun 28, 2011 4:38 pm
Posts: 7
Hey all you bashing gurus..

I have a files that have 6 instances of the string

&> /dev/null

I need to remove the 3rd and 4th instance in the file (not on the line)

I tried to use sed to do this:

Code:
sed -i 's/\&> \/dev\/null//3' go_ams_pop


but that did not work..

Any ideas?

thanks

~Dynacade
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choroba
 PostPosted: Sat Nov 12, 2011 4:36 am   
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Joined: Tue Apr 27, 2010 2:28 pm
Posts: 172
Location: Czech Republic
Code:
grep -n ^ $file |
    grep '&>/dev/null' |
    cut -f1 -d: |
    head -n4 | tail -n2 |
    sed 's,$,s=&>/dev/null==,' |
    sed -f- $file

How does it work? It numbers lines in the file, selects only those lines containing the string, takes their line numbers, selects the 3rd and 4th, and then does the replacement only at the given lines.
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jsz
 PostPosted: Sun Nov 13, 2011 11:17 am   
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Joined: Wed Jun 08, 2011 8:27 am
Posts: 159
Location: outer Shpongolia
Using a counter in awk(1).

Code:
awk '/&> \/dev\/null/ { o++; if (o ~ /(3|4)/) sub(/&> \/dev\/null/, _) } 1' file > file_tmp
mv file_tmp file


Using ed(1) (so no temporary file creation needed, but less understandable and modifiable):
Code:
ed -s file <<< $'/&> \/dev\/null/\n//\n//s,&> /dev/null,,\n//s\nw'
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crouse
 PostPosted: Mon Nov 14, 2011 10:31 pm   
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Joined: Sun May 15, 2005 9:36 pm
Posts: 644
Location: Des Moines, Iowa
jsz wrote:
Using ed(1) (so no temporary file creation needed, but less understandable and modifiable):
Code:
ed -s file <<< $'/&> \/dev\/null/\n//\n//s,&> /dev/null,,\n//s\nw'


Very nice :D
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jsz
 PostPosted: Tue Nov 15, 2011 10:58 am   
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Joined: Wed Jun 08, 2011 8:27 am
Posts: 159
Location: outer Shpongolia
crouse wrote:
jsz wrote:
Using ed(1) (so no temporary file creation needed, but less understandable and modifiable):
Code:
ed -s file <<< $'/&> \/dev\/null/\n//\n//s,&> /dev/null,,\n//s\nw'



Very nice :D


Thank you. : -)
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jsz
 PostPosted: Sun Apr 01, 2012 6:44 pm   
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Joined: Wed Jun 08, 2011 8:27 am
Posts: 159
Location: outer Shpongolia
Reading this and thinking differently.

Code:
ed -s file <<< $'/&> \/dev\/null/\n\n\ns///\n//s\nw'


It's actually shorter.
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