Some answers in Macaulay2 can be very wide, but many of them will be wrapped appropriately to fit in the width of a terminal window. Macaulay2 can successfully be used in a terminal window if care is taken not to display very wide objects, but most users will prefer to use the interface provided with emacs or with texmacs.
Macaulay2 uses the readline library and the history library to handle user input in a terminal window. The readline user interface documentation is available at http://tiswww.case.edu/php/chet/readline/rluserman.html. It can also be read with the command info readline. The history user interface documentation is available at http://tiswww.case.edu/php/chet/readline/history.html#SEC1. It can also be read with the command info history.
Name completion is implemented. Press the TAB key to automatically complete names of identifiers that have been only partially typed, if possible. Press TAB a second time to get a list of the possible completions when multiple choices exist.