4 Example: accessing the Unix passwd file

The Unix passwd file is a file with records spanning a single line each. The fields are separated by a single‘:’character. Here is an example of a line:

joe:hgdu3r3bce:53:100:Joe Johnson:/users/joe:/bin/bash

The following call defines a table for it:

?- new_table('/etc/passwd',
             [ user(atom),
               passwd(code_list),
               uid(integer),
               gid(integer),
               gecos(code_list),
               homedir(atom),
               shell(atom)
             ],
             [ field_separator(0':)
             ],
             H).

To find all people of group 100, use:

?- findall(User, in_table(H, [user(User), gid(100)], _), Users).