linux - sed: -i may not be used with stdin on Mac OS X

Question

I am using a bison parser in my project. When I run the following command:

sed -i y.tab.c -e "s/  __attribute__ ((__unused__))$/# ifndef __cplusplus
  __attribute__ ((__unused__));
# endif/"

I get this error sed: -i may not be used with stdin

The command works fine in linux machines. I am using Mac OS X 10.9. It throws an error only on mac os x. I am not sure why. Can anyone help?

Thanks

Answer 1

The problem is that Mac OS X uses the BSD version of sed, which treats the -i option slightly differently. The GNU version used in Linux takes an optional argument with -i: if present, sed makes a backup file whose name consists of the input file plus the argument. Without an argument, sed simply modifies the input file without saving a backup of the original.

In BSD sed, the argument to -i is required. To avoid making a backup, you need to provide a zero-length argument, e.g. sed -i '' y.tab.c ....

Your command, which simply edits y.tab.c with no backup in Linux, would attempt to save a backup file using 'y.tab.c' as an extension. But now, with no other file in the command line, sed thinks you want to edit standard input in-place, something that is not allowed.