How to run SWI-Prolog from the command line?

Question

Is there a way to just create a prolog script called hello.pl like this:

#!/usr/local/bin/swipl -q -s -t main

main:-
  write('Hello World\n').

And be able to run it from the terminal like this?

$ hello.pl
Hello World
$

When I do that it gives me this:

hello.pl: line 3: main:-: command not found
hello.pl: line 4: syntax error near unexpected token `'Hello World\n''
hello.pl: line 4: `  write('Hello World\n').'

I am able to get it working by writing this on the command line:

$ swipl -q -f hello.pl -t main
Hello World
$

But is there a way to just run the straight script as an executable instead?

Edit

Haven't yet been able to get this to work. Here is the output from the commands @Boris asked in the comments in his answer:

$ ls -l
total 8
-rwxr-xr-x  1 viatropos  staff  235 Aug 26 20:28 example.pl
$ cat example.pl
#!/usr/local/bin/swipl

:- set_prolog_flag(verbose, silent).

:- initialization main.

main :-
    format('Example script~n'),
    current_prolog_flag(argv, Argv),
    format('Called with ~q~n', [Argv]),
    halt.
main :-
    halt(1).
$ which swipl
/usr/local/bin/swipl
$ swipl --version
SWI-Prolog version 6.6.6 for x86_64-darwin13.1.0
$ ./example.pl
./example.pl: line 3: syntax error near unexpected token `('
./example.pl: line 3: `:- set_prolog_flag(verbose, silent).'
$

I am on Mac OSX 10.9.2, and installed swipl with homebrew via brew install swi-prolog --with-libarchive

Answer 1

ISO directive: initialization. This should work.

:- initialization main.

main :-
  write('Hello World\n').

edit sorry, I skipped over most interesting details. Here is a sample script, let's say saved in ~/test/main.pl

#!/home/carlo/bin/swipl -f -q

:- initialization main.

main :-
  current_prolog_flag(argv, Argv),
  format('Hello World, argv:~w\n', [Argv]),
  halt(0).

and made executable with

chmod +x ~/test/main.pl

then I get

~$ ~/test/main.pl
Hello World, argv:[]

~$ ~/test/main.pl as,dnj asdl
Hello World, argv:[as,dnj,asdl]

In script main.pl, I used the swipl path that results from building from source without admin privileges. The SWI-Prolog build process put bin and lib under ~/bin and ~/lib

Note: the -f flag disables loading the initialization ~/.plrc, and this could be necessary to get more 'strict control' over execution...

I'm currently unsure if the documentation page is up-to-date with current SW status. From some mailing list message, and my own efforts to reuse thea, seems that command line flags changed recently...

Answer 2

The other answer is more or less correct, however, how it works might depend on your OS. The most portable way to do it is, appartently:

$ cat example.pl
#!/path/to/your/swipl

:- set_prolog_flag(verbose, silent).

:- initialization main.

main :-
    format('Example script~n'),
    current_prolog_flag(argv, Argv),
    format('Called with ~q~n', [Argv]),
    halt.
main :-
    halt(1).

The difference here is that there is nothing on the shebang line apart from the path to swipl. Everything else is done using directives. On my OS, only that worked!

$ chmod u+x example.pl
$ example.pl foo bar baz
Example script
Called with [foo,bar,baz]

EDIT

It is probably cleaner to remove the shebang line altogether, and instead run from the command line:

$ swipl -s example.pl -- foo bar baz
Example script
Called with [foo,bar,baz]

Again, using a directive to set main/0 as the initialization goal saves you from having to explicitly do this on the command line. Calling swipl from the command line, on the other hand, lets your OS find where the executable is, instead of hard-coding this information in the script.

Answer 3

You can use initialization/2.

#!/path/to/swipl -q

:- initialization(main, program).

main :-
    write("Hello"), nl,
    halt.

Rationale:

• -q (--quiet) is used to suppress all informational messages, including informational messages that originate from the SWI-Prolog initialization file (~/.swiplrc). :- set_prolog_flag(verbose, silent). could be used instead, but it does not suppress informational messages that come from the initialization file.

• :- initialization(main, program). - program causes Prolog to exit with an error code on failure of main or on encountering an exception, rather than staying in the REPL.

• halt - Stops the program with exit code 0.

The above assumes that you wish to load the initialization file (~/.swipl) before running the program. If you do not want to load the initialization file, use #!/path/to/swipl -f -q as the shebang. This makes the script start up faster.

(Also, be sure to set the executable bit (chmod +x hello.pl) before running the script (./hello.pl))