Find and replace in file and overwrite file doesn't work, it empties the file

shell unix sed io-redirection
BBales picture BBales · Mar 2, 2011 · Viewed 720.2k times · Source

I would like to run a find and replace on an HTML file through the command line.

My command looks something like this:

sed -e s/STRING_TO_REPLACE/STRING_TO_REPLACE_IT/g index.html > index.html

When I run this and look at the file afterward, it is empty. It deleted the contents of my file.

When I run this after restoring the file again:

sed -e s/STRING_TO_REPLACE/STRING_TO_REPLACE_IT/g index.html

The stdout is the contents of the file, and the find and replace has been executed.

Why is this happening?

Answer

codaddict picture codaddict · Mar 2, 2011

When the shell sees > index.html in the command line it opens the file index.html for writing, wiping off all its previous contents.

To fix this you need to pass the -i option to sed to make the changes inline and create a backup of the original file before it does the changes in-place:

sed -i.bak s/STRING_TO_REPLACE/STRING_TO_REPLACE_IT/g index.html

Without the .bak the command will fail on some platforms, such as Mac OSX.

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