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).
SIGINT (Control-C) that terminates the process 
with status 1.
When main/0 is called interactively it simply calls main/1 with the arguments. This allows for debugging scripts as follows:
$ swipl -l script.pl -- arg ... ?- gspy(suspect/1). % setup debugging ?- main. % run program
When guided, three predicates are called in the calling module. opt_type/3 must be defined, the others need not. Note that these three predicates may be defined as multifile to allow multiple modules contributing to the provided commandline options. Defining them as discontiguous allows for creating blocks that describe a group of related options.
-. 
A single character implies a short option, multiple a long option. Long 
options use _ as word separator, user options may 
use either _ or -. Type is one of:
| Bnonneg|boolean, for an option http handles --http 
as http(true), --no-http as http(false), --http=3000 
and --http 3000 as http(3000). With an 
optional boolean an option is considered boolean if it is the last or 
the next argument starts with a hyphen (-).
--opt=value notation. This explicit value 
specification converts true, True,
TRUE, on, On, ON, 1 
and the obvious false equivalents to Prolog true or false. 
If the option is specified, Default is used. If --no-opt or
--noopt is used, the inverse of Default is used.
integer. Requires value >= 0.
integer. Requires value >= 1.
float, 
else convert as integer. Then check the range.
atom, but requires the value to be a member of List 
(enum type).
file
file, and check access using access_file/2. 
A value - is not checked for access, assuming the 
application handles this as standard input or output.
directory, and check access. Access is one of read
write or create. In the latter case the parent 
directory must exist and have write access.
term, but passes Options to term_string/3. 
If the option
variable_names(Bindings) is given the option value is set 
to the pair Term-Bindings.
FILE in e.g. -f FILE.
By default, -h, -? and --help 
are bound to help. If
opt_type(Opt, help, boolean) is true for some Opt, 
the default help binding and help message are disabled and the normal 
user rules apply. In particular, the user should also provide a rule for
opt_help(help, String).
halt(Code), exit with Code. Other 
goals are currently not supported.
false (default true), stop parsing after 
the first positional argument, returning options that follow this 
argument as positional arguments. E.g, -x file -y results 
in positional arguments [file, '-y']
debug. Other meaningful 
options are informational or warning. The help 
page consists of four sections, two of which are optional:
opt_help(help(header), String). 
It is optional.
Usage: <command> is by default [options] 
and can be overruled using opt_help(help(usage), String).
opt_help(help(footer), String). 
It is optional.
The help provided by help(header), help(usage) 
and help(footer) are either a simple string or a list of 
elements as defined by
print_message_lines/3. 
In the latter case, the construct \Callable can be used to 
call a DCG rule in the module from which the user calls argv_options/3. 
For example, we can add a bold title using
opt_help(help(header), [ansi(bold, '~w', ['My title'])]).
--debug='http(_)'.
debug(Topic). See debug/1 
and debug/3.
opt_type(..., ..., ...).	% application types
opt_type(Flag, Opt, Type) :-
    cli_debug_opt_type(Flag, Opt, Type).
% similar for opt_help/2 and opt_meta/2
main(Argv) :-
    argv_options(Argv, Positional, Options0),
    cli_parse_debug_options(Options0, Options),
    ...
This predicate may be called from main/1 to enter the Prolog toplevel rather than terminating the application after main/1 completes.