How does Mac's command line compare to Linux?

Mac OS X is a Unix OS and its command line is 99.9% the same as any Linux distribution. bash is your default shell and you can compile all of the same programs and utilities. There's no notable difference. You can also find various projects like MacPorts which provide package management for Mac.

Bash is bash so the shell and its built-ins are the same. But be aware that the behavior of some tools like ps or head can differ in the details thus your scripts might fail.

It's very similar, but if you know of any BSD v. Linux differences, expect the Mac to have the BSD behavior.