SWI-Prolog -- The user's initialisation file

2.2 The user's initialisation file

After the system initialisation, the system consults (see consult/1) the user's init file. This file is searched using absolute_file_name/3 using the path alias (see file_search_path/2) app_config. This is a directory named swi-prolog below the OS default name for placing application configuration data:

On Windows, the CSIDL folder CSIDL_APPDATA, typically C:\Documents and Settings\username\Application Data.

If the environment variable XDG_DATA_HOME is set, use this. This follows the free desktop standard.

The expansion of /.config.

The directory can be found using this call:

?- absolute_file_name(app_config(.), Dir, [file_type(directory)]). Dir = '/home/jan/.config/swi-prolog'.

After the first startup file is found it is loaded and Prolog stops looking for further startup files. The name of the startup file can be changed with the‘-f file’option. If File denotes an absolute path, this file is loaded, otherwise the file is searched for using the same conventions as for the default startup file. Finally, if file is none, no file is loaded.

The installation provides a file customize/init.pl with (commented) commands that are often used to customize the behaviour of Prolog, such as interfacing to the editor, color selection or history parameters. Many of the development tools provide menu entries for editing the startup file and starting a fresh startup file from the system skeleton.

See also the -s (script) and -F (system-wide initialisation) in section 2.4 and section 2.3.

Pasi Xyy said (2022-08-25T20:29:41):

If your installation can run XPCE, then it is possible to automatically set up user and xpce defaults with module swi_preferences.

Also manpce opens up tiny XPCE window in top left where you can select items from menu

These will open up a confirmation window if preferences files does not exist, else they will open up files in PCemacs

prolog_edit_preferences(prolog).
prolog_edit_preferences(xpce).

Harald Störrle said (2021-11-08T11:13:35):

Same on W10/W11, but it worked by saying

absolute_file_name('.', Dir, [file_type(directory)]).

However, a "init.pl" placed there is not being called on startup (using SWIPL 8.0.3). Chaning ...\boot\init.pl didn't make a change, either. Giving up. :_(

LogicalCaptain said (2020-07-26T11:33:39):

The example customize/init.pl file is in lib/swipl/customize/init.pl in the SWI-Prolog installation directory.

The text does not say so explicitly, but the initialization Prolog file must apparently actually be called init.pl.

In the home directory on Linux it is

$HOME/.config/swi-prolog/init.pl

Find it with

$ find "$HOME" -name init.pl 2>/dev/null

Jon Millen said (2020-05-23T14:43:08):

The absolute_file_name call failed on MacOS (Catalina) with "source_sink `app_config('.')' does not exist." Also, init.pl in my home directory is ignored. What else can I try? I cannot create .swipl or other dot-files on MacOS, even as admin. I don't see a preferences plist file in any standard library location with a relevant entry.

[edit] Never mind, I downloaded 8.1.32 and put init.pl in ~/.config/swi-prolog. My suggestion, for the benefit of non-powerusers who don't want to deal with dot-files, is to add a prolog goal: set_init_file or set_default_working_directory, that has a persistent effect, so that it will not have to be invoked on subsequent sessions.

C. M. Sperberg-McQueen said (2019-12-21T02:41:01):

The FAQ says that the user initialization file is .plrc (not init.pl, as the documentation for -f says). A comment on that FAQ page says (accurately, as far as I can tell) that the individual initialization file is .swiplrc.

I see that this has changed recently; it might be helpful to mention that behavior is (or may be) version dependent.

C. M. Sperberg-McQueen said (2019-12-21T02:29:36):

The OS default configuration directory will, the text says, under some circumstances be " The expansion of /.config." Missing tilde?

The text also says "The installation provides a file customize/init.pl with (commented) commands that are often used to customize the behaviour of Prolog, such as ..."

For what it's worth, I cannot find any customize/init.pl in the MacOS application package. And app_config appears to be unknown as an alias (perhaps because I did not in fact have a ~/.config/swi-prolog directory when I started trying to figure out why SWI Prolog was not starting in my home directory).