Did you know ... Search Documentation:
Predicate file_name_extension/3
Availability:built-in
file_name_extension(?Base, ?Extension, ?Name)
This predicate is used to add, remove or test filename extensions. The main reason for its introduction is to deal with different filename properties in a portable manner. If the file system is case-insensitive, testing for an extension will also be done case-insensitive. Extension may be specified with or without a leading dot (.). If an Extension is generated, it will not have a leading dot.
Tags are associated to your profile if you are logged in
Tags:
LogicalCaptain said (2021-02-27T10:42:38):0 upvotes 0 0 downvotes
Picture of user LogicalCaptain.

Arg naming

"Base" should be called "Core"

As in: "Name = CoreName . Extension", and "Name" is probably the "Basename" of a "Path"

Examples

Standard usage: the extension is the tailing substring up to the rightmost dot

?- file_name_extension(Base,Extension,"random.html").
Base = random,
Extension = html.
?- file_name_extension(Base,Extension,"random.html.html").
Base = 'random.html',
Extension = html.
?- file_name_extension(Base,Extension,"random.1.3.4..html").
Base = 'random.1.3.4.', % second dot belongs to base
Extension = html.
?- file_name_extension(Base,Extension,"random").
Base = "random",
Extension = ''.

Not a predicate because:

Ambiguity here:

?- file_name_extension(Base,Extension,"random").
Base = "random", % no dot
Extension = ''.
?- file_name_extension(Base,Extension,"random.").
Base = random, % still no
Extension = ''.

But only one solution going the other way (it's an atom btw):

?- file_name_extension(random,'',Name).
Name = random.

Doesn't care about preceding path:

?- file_name_extension(Base,Extension,"/usr/local/foo.bar").
Base = '/usr/local/foo',
Extension = bar.
?- file_name_extension(Base,Extension,"/usr/local/foo").
Base = "/usr/local/foo",
Extension = ''.

Should probably throw a domain error here:

?- file_name_extension(Base,Extension,"/usr/local/foo.bar/").
Base = "/usr/local/foo.bar/",
Extension = ''.

Edgy:

?- file_name_extension(Base,Extension,".bar").
Base = '',
Extension = bar.

Correct use with file_base_name

?- file_base_name("/foo/bar/baz.gz",Basename),
   file_name_extension(Corename,Extension,Basename).
Basename = 'baz.gz',
Corename = baz,
Extension = gz.