by Prolog packs, in a user specific directory or in a system-wide directory. See section 2.11.1.5.

2.11.1.1 Using PrologScript

A Prolog source file can be used directly as a Unix program using the Unix #! magic start. The Unix #! magic is allowed because if the first letter of a Prolog file is #, the first line is treated as a comment.^{12The #-sign can be the legal start of a normal Prolog clause. In the unlikely case this is required, leave the first line blank or add a header comment.} To create a Prolog script, use one of the two alternatives below as first line. The first can be used to bind a script to a specific Prolog installation, while the latter uses the default prolog installed in $PATH.

#!/path/to/swipl
#!/usr/bin/env swipl