dirname replacement about shellcheck

[koalaman]

The two are often interchangable, but in this case, for paths with trailing slashes, and in your unquoted case when the invoked name contains whitespace, the results are not identical. dirname and basename handle some edge cases well, even though it's slower and harder to use right. I'll keep it mind and see how helpful this suggestion actually is.

PS: dirname $0 is not a reliable way of getting the directory the script is in. In particular it fails when you invoke the script from $PATH.

[ptman]

I also think the checks on basename and dirname may be a bit aggressive