For Textmate there is a command line tool, mate, that can be installed. Once installed you just use `mate <file>` to open that file in text mate.

For application that don't have a command line tool, you can use the `open` command with the `-a` flag and the name of the application. i.e.

`open -a iTunes`

This also works for TextMate:

`open -a "TextMate 2"`

The executable file is located in the app's Contents/MacOS subfolder, so for TextMate 2, it would be:

`/Applications/TextMate\ 2.app/Contents/MacOS/TextMate`

But if you run it from the command line like that, it will hang the shell until the application is quit.