Use the terminal's autocomplete path feature for input to a shell script

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http://unix.stackexchange.com – I want to make a script that: (1) Gets a path giving the user the ability to use tab to autocomplete, then (2) gets a filename from the user, and then (3) creates a file at that path with extension .txt. My question is: How do I do 1.? How do I tell bash to ask for input that is an "autocompletable" path, preferably with part of the path (say ~/x/) already filled out by default? Note: the paths will almost always include spaces. (HowTos)