Before you start casting, you will want a report of all the characters you've written into your movie so that you know what casting slots you must fill.
Screenplay-character searches for all the CAPITALIZED character names with dialogue. It will also catch transitions, although it uses grep to eliminate those false positives before it finishes. Still, you should review the output just to make sure you're not doing a casting call for a character named DISSOLVE TO or AND THEN HE FLOORS IT.
By default, this list is formatted for printing with appropriate headers and page breaks as needed. If, however, you prefer to keep the reports digital, you can specify an output file with the .org extension, such as characters.org and you will end up with a document without enforced page breaks or headers, formatted for use in org-mode's outline view.
Using screenplay-character is the same as screenplay-location:
$ screenplay-character myGreatMove.screenplay character.report
Of course, if you ever need help with any of the screenplay-tool commands, simply type in screenplay-help or view the man page for the command you are using.