Renaming and Deleting Files

library(files) defines four predicates pertaining to deleting and renaming files. rename/2 and dec10_rename/2 are identical replacements for the DEC-10 Prolog/C-Prolog rename/2 command. They should only be used to convert old code to Quintus Prolog. New programs should use delete_file/1 and rename_file/2.

delete_file(+FileName)

FileName should be an atom naming a file that currently exists and can be deleted. If so, the file it names is deleted, and the command succeeds. If not, an error exception is raised. and the command fails. Examples:

          | ?- delete_file('ask.otl').
          
          yes
          
          | ?- delete_file('does_not_exist').
          ! Existence error in delete_file/1
          ! file nosuch does not exist
          ! O/S error : No such file or directory
          ! goal:  delete_file(does_not_exist)
          

          | ?- unix(system('cat </dev/null >search.d/tmp')),
               unix(system('chmod a-w search.d')),
               delete_file('search.d/tmp').
          ! O/S error : Permission denied
          ! goal:  delete_file('search.d/tmp')
          

          | ?- delete_file("tmp").
          ! Type error in argument 1 of delete_file/1
          ! symbol expected, but [116,109,112] found
          ! goal:  delete_file([116,109,112])
          
          | ?- unix(system('rm tmp')).
          rm: override protection 444 for tmp? n
          yes             % did NOT delete the file
          
          | ?- delete_file(tmp).
          
          yes             % **DID** delete the file
          

This last example is important: the rm command (see rm(1)) checks the permission bits of the file (see chmod(1)) and asks you whether you really want to delete a file that you do not have write permission for, even if you have permission to delete it. delete_file/1 does not do this.

rename_file(+OldName, +NewName)

OldName should be an atom naming a file that currently exists and can be renamed, and NewName should be a valid filename to which the file can be renamed. If so, the file will be renamed, and the command will succeed. If not, an error exception will be raised. Examples:

          | ?- rename_file(does_not_exist, imaginary).
          ! Existence error in rename_file/2
          ! file does_not_exist does not exist
          ! O/S error : No such file or directory
          ! goal:  rename_file(does_not_exist,imaginary)
          

rename_file/2 and delete_file/1 have no effect on currently open streams, whether opened by open/3, see/1, or tell/1.

What will happen if you continue to use streams that used to be connected to files affected by these commands is system-dependent. Under UNIX, input will continue to come from a file as if it had not been renamed, and output will continue to go to a file as if it had not been renamed. For example:

          % prolog
          | ?- compile(library(files)).
          <output of compile/1>
          yes
          
          | ?- open(fred, write, OutputStream),
               open(fred, read,  InputStream ),
               delete_file(fred),
               format(OutputStream, 'foo.~n', []),
               flush_output(OutputStream),
               read(InputStream, Term),
               close(OutputStream),
               close(InputStream).
          
          OutputStream = '$stream'(10,3),
          InputStream = '$stream'(11,4),
          Term = foo
          

rename(+OldName, +NewName)

This command is identical to dec10_rename/2 below.

dec10_rename(+OldName, +NewName)

This predicate is similar, but not identical, to the DEC-10 Prolog/C-Prolog command rename/2, and is provided solely for the sake of compatibility. If you are converting existing DEC-10 Prolog or C-Prolog code to Quintus Prolog, the fact that rename/2 does close the file and is sensitive to the fileerrors flag should be useful. In new programs we recommend the use of rename_file/2 and delete_file/1. OldName and NewName must be atoms, otherwise an error is reported and the command fails (this is not affected by the setting of the fileerrors flag). If NewName is [], the file named by OldName is deleted, otherwise it is renamed to NewName. If the rename cannot be performed, what happens next depends on the setting of the fileerrors flag (see the reference page for prolog_flag/3). If fileerrors is on, an error exception is raised. If fileerrors is off, the command fails quietly. Examples:

          | ?- prolog_flag(fileerrors, Setting).
          
          Setting = on
          
          | ?- dec10_rename(2, 1).
          ! Type error in argument 1 of dec10_rename/2
          ! symbol expected, but 2 found
          ! goal:  dec10_rename(2,1)
          

          | ?- dec10_rename(does_not_exist, []).
          ! Existence error in dec10_rename/2
          ! file does_not_exist does not exist
          ! O/S error : No such file or directory
          ! goal:  dec10_rename(does_not_exist,[])
          
          | ?- prolog_flag(fileerrors, _, off).
          
          yes
          

          | ?- dec10_rename("old", "new").
          ! Type error in argument 1 of dec10_rename/2
          ! symbol expected, but [111,108,100] found
          ! goal:  dec10_rename([111,108,100],[110,101,119])
          
          | ?- dec10_rename(does_not_exist, []).
          
          no