sed command with -i option failing on Mac, but works on Linux

I've successfully used the following sed command to search/replace text in Linux:

sed -i 's/old_link/new_link/g' *

However, when I try it on my Mac OS X, I get:

"command c expects \ followed by text"

I thought my Mac runs a normal BASH shell. What's up?

EDIT:

According to @High Performance, this is due to Mac sed being of a different (BSD) flavor, so my question would therefore be how do I replicate this command in BSD sed?

EDIT:

Here is an actual example that causes this:

sed -i 's/hello/gbye/g' *

Solution

The -i option (alternatively, --in-place) means that you want files edited in-place, rather than streaming the change to a new place.

Modifying a file in-place suggests a need for a backup file - and so a user-specified extension is expected after -i, but the parsing of the extension argument is handled differently under GNU sed & Mac (BSD) sed:

GNU : "If no extension is supplied, the original file is overwritten without making a backup." - effectively, you can omit specify a file extension altogether. The extension must be supplied immediately after the -i, with no intervening space.
Mac (BSD) : "If a zero-length extension is given, no backup will be saved." - you must supply an extension, but it can be the empty string '' if you want, to disable the backup.

So GNU & Mac will interpret this differently:

sed -i 's/hello/bye/g' jkl.txt

GNU : No extension is supplied immediately after the -i, so create no backup, use s/hello/bye/g as the text-editing command, and act on the file jkl.txt in-place.
Mac (BSD) : Use s/hello/bye/g is the backup file extension (!), use jkl.txt as the text-editing command, but uh-oh!: the command code given there is j (not, eg s, a valid command code for substitution), so error with invalid command code j.

Portable solution

To get a portable command, you can use this invocation, that works across both GNU sed and Mac (BSD) sed in Mac OS X Mavericks (v10.9, released June 2013) and above:

sed -i'' -e 's/hello/bye/g' jkl.txt

Placing the extension immediately after the -i (eg -i'' or -i'.bak', without a space) is what GNU sed expects, and is now accepted by Mac (BSD) sed too, though it wasn't tolerated by earlier versions (eg with Mac OS X v10.6, a space was required after -i, eg -i '.bak').

The -e parameter allows us to be explicit about where we're declaring the edit command.

Until Mac OS was updated in 2013, there wasn't any portable command across GNU and Mac (BSD), as these variants also failed:

sed -i -e ... - does not work on OS X as it creates -e backups
sed -i '' -e ... - fails on GNU

When there wasn't a sed command working on all platforms, you could have tried using another command to achieve the same result, e.g. perl -i -pe's/old_link/new_link/g' *.