Selection of the variation is accomplished via command-line options:

• options are introduced by a - ("minus" or "dash")
• options have a "short" form, - followed by a single letter   (e.g. -v)
• options have a "long" form, -- followed by a word   (e.g. --verbose)
• short form options can usually be combined   (e.g. -av  vs  -a -v)
• --help (or -?) often gives a list of all command-line options