which

Alias:

$ which ls
ls is an alias for ls -G`

Function:

$ which upgrade-deps
upgrade-deps () {
if [[ -n "$(git status --porcelain)" ]]
then
...

Type

$ type upgrade-deps
upgrade-deps is a shell function from /Users/mcurrin/.aliases`

$ type ls
ls is an alias for ls -G

ln

Check if a symlink is valid.

If valid:

$ ln -s abc def
$ ln def
ln: ./def: File exists

If not valid:

$ ln -s abc def
$ rm abc
$ ln def
ln: def: No such file or directory