Quick note about sed’s edit in place option
From the sed manpage:
-i extension
Edit files in-place, saving backups with the specified extension.
If a zero-length extension is given, no backup will be saved. It
is not recommended to give a zero-length extension when in-place
editing files, as you risk corruption or partial content in situ-
ations where disk space is exhausted, etc.This doesn’t work:
sed -i -e's/apples/oranges/' file.txt
The key thing here is that the extension after the -i flag is not optional. If you leave it off, sed assumes you’ll be entering it via stdin, which isn’t allowed and yields this error:
sed: -i may not be used with stdin
The solution is to send a zero-length extension like this:
sed -i '' -e's/apples/oranges/' file.txt
Careful with this, it could be really dangerous with poorly crafted commands.
Thanks for the tip. I was having trouble getting the edit-in-place option to work.
Thanks for your excellent tip. Has saved me from weird backup files that caused alot of headaches
It seems that some versions of sed require the argument after -i and others do not.
With GNU sed version 4.1.x, it seems that the -i does not require an argument and specifying an empty argument after it actually fails:
sed -i ” -e’s/apples/oranges/’ file.txt
sed: can’t read : No such file or directory
sed -i -e’s/apples/oranges/’ file.txt
(works)
Thanks for clarifying that!
Was recently fiddling and ran into the -i issue… -i ” failed, but -i” worked. Fedora Core 11 x86_64.
Thanks Joe – it is a really helpful tip!
As for me, those versions of sed which require user to specify the argument for the -i option demonstrate the more secure way in processing potentially destructive commands. In other words such versions of sed stimulate user to read the documentation carefully.
Thanks for that. I was struggling!
Thanks, I was excited to find this, but I couldn’t get -i to work in FreeBSD 8.0 period; that is with or without extension. Always get the same error (‘sed: -i may not be used with stdin’) with all the example lines below:
sed -i ‘tmp’ -e ‘s/apples/oranges/’ <test.txt
sed -i '' -e 's/apples/oranges/' <test.txt
sed -i'' -e 's/apples/oranges/' <test.txt
sed -i' ' -e 's/apples/oranges/' <test.txt
and so forth.
These work:
sed 's/apples/oranges/' testnew.txt
sed -e’s/apples/oranges/’ testnew.txt
sed -e ‘s/apples/oranges/’ testnew.txt