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Using the command SED

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# 1  
Old 01-06-2012
Using the command SED
I am trying to use sed with substitute to replace a section of text in a fileA.

Question 1:
If I want to want replace the "search" string with "replace" string inside fileA. I understand that I can use
Code:
sed 's/search/replace' < fileA >fileB

I also tried to do <fileA >fileA, but it doesn't work. Why is that? I don't want an extra file, fileB.

Question 2:
My main question. Inside the comand sed 's/search/replace' < fileA >fileB, the string "search" and "replaced" are actually inside fileC and fileD. How do I write the command? Thanks!

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Mod Comment How to use code tags when posting data and code samples.
Last edited by Franklin52; 01-06-2012 at 06:08 PM.. Reason: Please use code tags for data and code samples, thank you
# 2  
Old 01-06-2012
This is one way of doing it:
Code:
sed 's/Search/Replace/' Input > Output

# 3  
Old 01-06-2012
Which system are you using? UNIX tool behave differently between systems
Quote:
Originally Posted by jyang72211
Question 1:
If I want to want replace the "search" string with "replace" string inside fileA. I understand that I can use

sed 's/search/replace' < fileA >fileB
I think you're missing the last slash. And if your sed takes files as argument, the `<` is useless:
Code:
sed 's/search/replace/' fileA >fileB

Quote:
Originally Posted by jyang72211
I also tried to do <fileA >fileA, but it doesn't work. Why is that? I don't want an extra file, fileB.
Try -i option:
Code:
sed -i 's/search/replace/' fileA

Quote:
Originally Posted by jyang72211
Question 2:
My main question. Inside the comand sed 's/search/replace' < fileA >fileB, the string "search" and "replaced" are actually inside fileC and fileD. How do I write the command? Thanks!
If fileC and fileD contain multiple search & replace patterns, you need to write a script that read each line in fileC and fileD to variables and use them in your sed command:
Code:
sed 's/'"$search"'/'"$replace"'/' fileA

This User Gave Thanks to tukuyomi For This Post:
jyang72211
# 4  
Old 01-06-2012
1)
Code:
sed -i s/search/replace/' fileA

2) Assume that fileC, fileD contains just one string.
try this:
TO_GREP=`cat fileC`
TO_REP=`cat fileD`
Code:
sed "s/$TO_GREP/$TO_REP/" fileA

This User Gave Thanks to greet_sed For This Post:
jyang72211
# 5  
Old 01-07-2012
I am working on a xp machine, and I am telneting to a linux system.
# 6  
Old 01-07-2012
Code:
root@bt> cat fileA
Linux Unix Solaris Windows
root@bt> cat fileC
Windows
root@bt> cat fileD
Oops

root@bt> sed "s/$(<fileC)/$(<fileD)/g" fileA
Linux Unix Solaris Oops

Storing it in fileB
Code:
root@bt> sed "s/$(<fileC)/$(<fileD)/g" fileA > fileB
root@bt> cat fileB
Oopsx Unix Solaris Oops

Modifying the fileA inline using -i option in sed
Code:
root@bt> sed -i "s/$(<fileC)/$(<fileD)/g" fileA 
root@bt> cat fileA
Oopsx Unix Solaris Oops

HTH
--ahamed
This User Gave Thanks to ahamed101 For This Post:
jyang72211
# 7  
Old 01-07-2012
Quote:
Originally Posted by greet_sed
1)
Code:
sed -i s/search/replace/' fileA

2) Assume that fileC, fileD contains just one string.
try this:
TO_GREP=`cat fileC`
TO_REP=`cat fileD`
Code:
sed "s/$TO_GREP/$TO_REP/" fileA


When I do 2), can I execute the 3 lines one at a time?
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