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Using grep output as input for sed command

 
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# 1  
Old 04-07-2010
Data Using grep output as input for sed command
Hi,

I would like to know if this is possible, and if so what can i do to make this work.

I would like to grep a line X from fileA and then use the output to replace a word Y in fileB.

Code:
grep "line X" fileA | sed -e 's/Y/X/g' > outfile

this statement does not work, as i do not know how to get the sed command to recognize the grep output.

Any suggestions?

edit by bakunin: please use code-tags for posting code, commands or file contents
Last edited by bakunin; 04-07-2010 at 01:07 PM..
# 2  
Old 04-07-2010
Hi,

The below command is working for Korn shell:

HTML Code:
grep "AAA" file1.txt | sed 's/A/Z/g' > output.txt
Following is the output of the command:

HTML Code:
$ cat file1.txt
AAA
BBB
CCC
DD
EE
$ grep "AAA" file1.txt | sed 's/A/Z/g' > output.txt
$ cat output.txt
ZZZ
Hope this will help you. Smilie
Thanks!
# 3  
Old 04-07-2010
Using grep output as input for sed command
Hi,

Thanks much, unfortunatly, its not quite what i need. I need to be able to go into my FileB and using the grep output from FileA do a replace command on one of my words in file A with the grep output.

I forgot to add in the fileB in my last line of code, but heres what i was going for
Code:
grep "line X" fileA | sed -e fileB 's/Y/X/g' > outfile

again not sure if there is a way to be able to use the grep output in the sed command.

Best,
Claire
Last edited by bakunin; 04-07-2010 at 01:07 PM..
# 4  
Old 04-07-2010
you haven't supplied an example, but i suppose the output of grep can be multiple lines, yes? If so:

Code:
#! /bin/ksh

grep "Expr" /path/to/file | while read source ; do
     print - "now replacing \"$source\" with \"target\""
     sed 's/'"$source"'/target/' /path/to/file2 > /path/to/file2.tmp
     mv /path/to/file2.tmp /path/to/file2
done

This will grep the file "/path/to/file" for lines containing the expression "Expr" and feed every line found this way into the variable "$source", which in turn is successively searched for in file /path/to/file2 and replaced by "target". Notice the quoting of the variable inside the sed-line, which is necessary to make sure the resulting command is a continuous string. The print command is only meant as an explanatory device and not necessary.

I hope this helps.

bakunin
# 5  
Old 04-07-2010
Bug Using grep output as input for sed command
Thank you so much, this has made my day.

Just had one adjustment, and that was to switch the 'target' and the 'source' for the find and replace to work correctly (",)

Code:
#! /bin/ksh

grep "Expr" /path/to/file | while read source ; do
       print - "now replacing \"$source\" with \"target\""
       sed 's/target/'"$source"'/' /path/to/file2 > /path/to/file2.tmp
       mv /path/to/file2.tmp /path/to/file2
done


Really appreciate your help, thanks again

edit by bakunin: please use the code-tags i supplied in your post yourself henceforth. Thank you.
Last edited by cavanac2; 04-08-2010 at 06:50 AM.. Reason: to keep original code supplied by previous reply
# 6  
Old 04-08-2010
Ahem, ...

As much as i appreciate your appreciation i have a feeling that the reasoning behind your script is somewhat flawed: When you first run the loop the sed-statement will change all occurrences of "target" to whatever the grep gave as first hit. When the loop is executed for the second (or any subsequent) time it would try to change "target" to whatever grep provided as secod hit, but there will be no more instances of "target", because they all have been changed in the first run, yes?

This will only work if any subsequent expression will hit a subset of the previous one, which has just got changed. In this case i suppose there would be more efficient (and more elegant) ways to achieve the same result. How about you state your complete problem here and we have a review?

I hope this helps.

bakunin
# 7  
Old 04-08-2010
Using grep output as input for sed command
you will have to forgive me, i am still very much in the beginning learning stages here

Basically i have a file1 which has one line of information which i need to place into a specific position in file2, lets call this line XXX
I wanted to 'grep' the XXX line from file1 and then pipe it to file2. In file 2 i had a specific location that i wanted XXX to go into, this location i labeled in my file as YYY.
Where source = 'XXX' and Target='YYY'

Code:
#! /bin/ksh

grep "XXX" /path/to/file | while read source ; do
       print - "now replacing \"$source\" with \"target\""
       sed 's/YYY/'"$source"'/' /path/to/file2 > /path/to/file2.tmp
       mv /path/to/file2.tmp /path/to/file2
done

This seems to work quite well, as it goes into my file2 and replaces 'YYY' with 'XXX' from the original file1.

i hope that is ok?

Best
 
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