By default, SWI-Prolog is installed as `swipl'. The command line arguments of SWI-Prolog itself and its utility programs are documented using standard Unix man pages. SWI-Prolog is normally operated as an interactive application simply by starting the program:
machine% swipl Welcome to SWI-Prolog ... ... 1 ?-
After starting Prolog, one normally loads a program into it using
consult/1, 
which may be abbreviated by putting the name of the program file between 
square brackets. The following goal loads the file
likes.pl containing clauses for the predicates likes/2 :
?- [likes]. % likes compiled, 0.00 sec, 17 clauses true. ?-
After this point, Unix and Windows users unite, so if you are using Unix please continue at section 2.1.2.
After SWI-Prolog has been installed on a Windows system, the following important new things are available to the user:
swipl containing the executables, 
libraries, etc., of the system. No files are installed outside this 
directory.
.pl is associated with the program
swipl-win.exe. Opening a .pl file will cause
swipl-win.exe to start, change directory to the directory in 
which the file to open resides, and load this file.
The normal way to start the likes.pl file mentioned in
section 2.1.1.1 is 
by simply double-clicking this file in the Windows explorer.
After loading a program, one can ask Prolog queries about the 
program. The query below asks Prolog what food `sam' likes. The system 
responds with X = <value> if it can prove 
the goal for a certain
X. The user can type the semi-colon (;) or spacebar6On 
most installations, single-character commands are executed without 
waiting for the RETURN key. 
if (s)he wants another solution. Use the return 
key if you do not want to see the more answers. Prolog completes the 
output with a full stop (.) if the user uses the return 
key or Prolog
knows there are no more answers. If Prolog cannot find (more) 
answers, it writes false. Finally, Prolog answers using an error 
message to indicate the query or program contains an error.
?- likes(sam, X). X = dahl ; X = tandoori ; ... X = chips. ?-
Note that the answer written by Prolog is a valid Prolog program that, when executed, produces the same set of answers as the original program.7The SWI-Prolog top level differs in several ways from traditional Prolog top level. The current top level was designed in cooperation with Ulrich Neumerkel.