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use awk to edit a file..pls help

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# 1  
Old 07-18-2010
use awk to edit a file..pls help
hey i want to over write the fourth field of a ':' delimited file by first finding the required row by using grep.
i have done the following
Code:
cat file | grep no. | awk -F ':' { $4=count; print $1:$2:$3:$4;}


the correct values are being printed but nothin is bein added to the file..please help.What is wrong ?
Last edited by Scott; 07-18-2010 at 07:56 AM.. Reason: Please use code tags
# 2  
Old 07-18-2010
Hi
awk does not change your files in place. You have to take care of changing it by re-direction and etc..

Guru.
# 3  
Old 07-18-2010
Hi.

awk writes to standard output (the screen), not back to the file.

With awk, you can do this:

Code:
awk -F ":" -v OFS=: ' /no./ $4="new value" ' file > new_file && cp new_file file && rm new_file

# 4  
Old 07-18-2010
hey thanx for the replies
@scottn
Will this keep my other rows of the file intact and not affect them. when i use the cp command will it copy to the same row location?
# 5  
Old 07-18-2010
Oops. There was an error in my script!

Code:
awk -F ":" -v OFS=: ' /no./ { $4="new value" } 1' file > new_file && cp new_file file && rm new_file

To answer your questions:
  • Only rows matching what your previous grep did are changed
  • This writes to a temporary file with the new values, then replaces the original file with the new file (with the new values)
# 6  
Old 07-18-2010
hey man!! thanx for the help...correct results now....thanx a lot...
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