4.34 Terminal Control

The following predicates form a simple access mechanism to the Unix termcap library to provide terminal-independent I/O for screen terminals. These predicates are only available on Unix machines. The SWI-Prolog Windows console accepts the ANSI escape sequences.

tty_get_capability(+Name, +Type, -Result)

Get the capability named Name from the termcap library. See termcap(5) for the capability names. Type specifies the type of the expected result, and is one of string, number or bool. String results are returned as an atom, number results as an integer, and bool results as the atom on or off. If an option cannot be found, this predicate fails silently. The results are only computed once. Successive queries on the same capability are fast. This predicate can raise several exceptions if the terminal environment is incomplete, notably if the environment variable TERM does not exist or there is no matching entry in the termcap database.

tty_goto(+X, +Y)

Goto position (X, Y) on the screen. Note that the predicates line_count/2 and line_position/2 will not have a well-defined behaviour while using this predicate.

tty_put(+Atom, +Lines)

Put an atom via the termcap library function tputs(). This function decodes padding information in the strings returned by tty_get_capability/3 and should be used to output these strings. Lines is the number of lines affected by the operation, or 1 if not applicable (as in almost all cases).

tty_size(-Rows, -Columns)

Determine the size of the terminal. Platforms:

Unix

If the system provides ioctl calls for this, these are used and tty_size/2 properly reflects the actual size after a user resize of the window. The ioctl is issued on the file descriptor associated with the user_input stream. As a fallback, the system uses tty_get_capability/3 using li and co capabilities. In this case the reported size reflects the size at the first call and is not updated after a user-initiated resize of the terminal.

Windows

Getting the size of the terminal is provided for swipl-win.exe. The requested value reflects the current size. For the multithreaded version the console that is associated with the user_input stream is used.