bug#71682: sed -i '' returns error but still modify target file

[Renato Botelho]

I'm writing a script that needs to run with both GNU and BSD sed 
implementations.  I know GNU sed accepts -i without any parameter while 
in BSD implementation it's mandatory.  I also know that if I use -i'' 
without spaces between -i and '' it works on both implementations and my 
problem is solved.

But I believe the behavior of GNU sed when there is a space between -i 
and '' is not correct.  It prints an error message and returns code 2 
but it still modifies the file.  Here is an example:

$ echo abcd > /tmp/f
$ sed -i '' -e 's/abcd/dcba/' /tmp/f
sed: can't read : No such file or directory
$ echo $?
2
$ cat /tmp/f
dcba

--
Renato Botelho