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sed find and replace multiple lines

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# 1  
Old 04-03-2009
sed find and replace multiple lines
I am new to linux and would like to modify the contents of a file preferably using a one line. The situation is as follows

<start>
some lines
"I am the string"
"replace string"
more lines here
<end>

In the above example,On encountering "I am the string", the "replace string "should be modified to say "string replaced"

i tried doing the following

sed -e 's/"I am the string"\n"replace string"/"I am the string"\n"string replaced"' myfile.txt

Also how do I make the modifications reflect in the file. its only diplaying at the terminal
# 2  
Old 04-03-2009
i have a file say file.txt having following contents

Code:
<tags>match the string</tags>
<tags>match</tags>

later the file should be(preferably with the same file name"file.txt")

Code:
<tags>match the string</tags>
<tags>replaced</tags>

The replace must be done if it encounters the first line only.
Can you give me a single line command for this?

This seemed more precise

Thank you
Last edited by Yogesh Sawant; 04-03-2009 at 04:25 PM.. Reason: added code tags
# 3  
Old 04-03-2009
what have you done so far?
# 4  
Old 04-03-2009
sed only operates on the line contained in its buffer, so to work on multiple lines you need to read more lines into the buffer. Depending on what all you want to do there are flags for read ahead buffer and read behind buffers. Also sed just outputs to screen so you have to redirect the output to a new file, then copy or move the new file to the original file name. I would always make a backup of the original file prior to modifications.
Code:
#sed -e 's/"I am the string"\n"replace string"/"I am the string"\n"string replaced"' 
sed -e '/"I am the string"/N;s/"replace string"/"string replaced"/' myfile.txt > myfile_new.txt

# 5  
Old 04-03-2009
Quote:
Originally Posted by supersimha
I am new to linux and would like to modify the contents of a file preferably using a one line. The situation is as follows

<start>
some lines
"I am the string"
"replace string"
more lines here
<end>

In the above example,On encountering "I am the string", the "replace string "should be modified to say "string replaced"

i tried doing the following

sed -e 's/"I am the string"\n"replace string"/"I am the string"\n"string replaced"' myfile.txt

Also how do I make the modifications reflect in the file. its only diplaying at the terminal

Check this
Code:
nawk '$0 ~/findstring/ {print $0;getline;gsub(/replace string/,"replaced string");print}' datafile > datafile1

# 6  
Old 04-03-2009
Quote:
Originally Posted by siquadri
Check this
Code:
nawk '$0 ~/findstring/ {print $0;getline;gsub(/replace string/,"replaced string");print}' datafile > datafile1


In place of findstring use I am the String
# 7  
Old 04-04-2009
Try this:

Quote:
perl -i -ne 's/I am the string/replace string /; print; ' file
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