A.21 library(main): Provide entry point for scripts

See also

- library(optparse) for comprehensive option parsing.
- library(prolog_stack) to force backtraces in case of an uncaught exception.
- XPCE users should have a look at library(pce_main), which starts the GUI and processes events until all windows have gone.

This library is intended for supporting PrologScript on Unix using the #! magic sequence for scripts using commandline options. The entry point main/0 calls the user-supplied predicate main/1 passing a list of commandline options. Below is a simle echo implementation in Prolog.

#!/usr/bin/env swipl

:- initialization(main, main).

main(Argv) :-
    echo(Argv).

echo([]) :- nl.
echo([Last]) :- !,
    write(Last), nl.
echo([H|T]) :-
    write(H), write(' '),
    echo(T).

main

Call main/1 using the passed command-line arguments. Before calling main/1 this predicate installs a signal handler for SIGINT (Control-C) that terminates the process with status 1.

[det]argv_options(+Argv, -RestArgv, -Options)

Generic transformation of long commandline arguments to options. Each --Name=Value is mapped to Name(Value). Each plain name is mapped to Name(true), unless Name starts with no-, in which case the option is mapped to Name(false). Numeric option values are mapped to Prolog numbers.

See also

library(optparse) provides a more involved option library, providing both short and long options, help and error handling. This predicate is more for quick-and-dirty scripts.