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SED Command Returning a Blank File

 
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# 1  
Old 02-25-2003
SED Command Returning a Blank File
I have a file called get_columns.sh that I would like to replace $2 with $3. I have the following sed command written that works

sed s/'$3'/'$2'/g get_columns.sh > output.txt

However, when I try the command below, the file is empty.

sed s/'$3'/'$2'/g get_columns.sh > get_columns.sh

Thanks for your assistance.

Dave
# 2  
Old 02-25-2003
You can't use the same file for input and output. The shell is destroying your input file by preparing to to write into it. This is done before the sed command even gets a chance to run.

Send the output to a tmpfile or something, then
mv tmpfile get_columns.sh
# 3  
Old 02-27-2003
Thanks for the info. The book I was using told me I could re-direct to the same file. Thanks again.
 
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