Not compatible with OSX

[bryanrossUK]

Great work! Just one wee gotcha I hit that might be easy to fix...

grep on my mac throws an error if you try to use an empty input file. Critically, because this is used by docker-gc here and here, it means no containers or images are ever removed.

I think one potential work around would be to ensure that $EXCLUDE_IDS_FILE and $EXCLUDE_CONTAINERS_IDS_FILE have at least one line in them (perhaps something that will never match like '_FOO_'.

eg.

$ grep --version
grep (BSD grep) 2.5.1-FreeBSD

$ cat containers.reap.tmp
6bf92fe32e92765d85b381325e702349c8bd1edb44df1537addbc593b97c1942

$ cat exclude_container_ids

$ cat containers.reap.tmp | grep -v -f exclude_container_ids
Exit 1

$ echo '_FOO_' > exclude_container_ids

$ cat containers.reap.tmp | grep -v -f exclude_container_ids
6bf92fe32e92765d85b381325e702349c8bd1edb44df1537addbc593b97c1942

[rohansingh]

We don't really target OS X and I don't see that changing in the future due to the limited resources available for this project. If you'd like to use docker-gc on an OS X machine, I'd recommend running it as a Docker image (see README).