Redirect output from sed 's/c/d/' myFile to myFile

Question

I am using sed in a script to do a replace and I want to have the replaced file overwrite the file. Normally I think that you would use this:

% sed -i \'s/c         


        

Answer 1

Kernighan and Pike in The Art of Unix Programming discuss this issue. Their solution is to write a script called overwrite, which allows one to do such things.

The usage is: overwrite file cmd file.

# overwrite: copy standard input to output after EOF

opath=$PATH
PATH=/bin:/usr/bin

case $# in
0|1)   echo 'Usage: overwrite file cmd [args]' 1>&2; exit 2
esac

file=$1; shift
new=/tmp/overwr1.$$; old=/tmp/overwr2.$$
trap 'rm -f $new $old; exit 1' 1 2 15  # clean up

if PATH=$opath "$@" >$new
then
       cp $file $old           # save original
       trap '' 1 2 15          # wr are commmitted
       cp $new $file
else
       echo "overwrite: $1 failed, $file unchanged" 1>&2
       exit 1
fi
rm -f $new $old

Once you have the above script in your $PATH, you can do:

overwrite manipulate sed 's/cat/dog/' manipulate

To make your life easier, you can use replace script from the same book:

# replace: replace  str1 in files with str2 in place
PATH=/bin:/usr/bin

case $# in
    0|2) echo 'Usage: replace str1 str2 files' 1>&2; exit 1
esac

left="$1"; right="$2"; shift; shift

for i
do
    overwrite $i sed "s@$left@$right@g" $i
done

Having replace in your $PATH too will allow you to say:

replace cat dog manipulate