| • File System Concepts | ||
Dictionary | ||
|---|---|---|
| • directory | ||
| • probe-file | ||
| • ensure-directories-exist | ||
| • truename | ||
| • file-author | ||
| • file-write-date | ||
| • rename-file | ||
| • delete-file | ||
| • file-error | ||
| • file-error-pathname | ||
This section describes the Common Lisp interface to file systems. The model used by this interface assumes that files are named by filenames, that a filename can be represented by a pathname object, and that given a pathname a stream can be constructed that connects to a file whose filename it represents.
For information about opening and closing files, and manipulating their contents, see Chapter 21 (Streams).
The next figure lists some operators that are applicable to files and directories.
|
Figure 20.1: File and Directory Operations
| • Coercion of Streams to Pathnames | ||
| • File Operations on Open and Closed Streams | ||
| • Truenames |
A stream associated with a file is either a file stream or a synonym stream whose target is a stream associated with a file. Such streams can be used as pathname designators.
Normally, when a stream associated with a file is used as a pathname designator, it denotes the pathname used to open the file; this may be, but is not required to be, the actual name of the file.
Some functions, such as truename and delete-file,
coerce streams to pathnames in a different way that
involves referring to the actual file that is open, which might
or might not be the file whose name was opened originally. Such special
situations are always notated specifically and are not the default.
Next: Truenames, Previous: Coercion of Streams to Pathnames, Up: File System Concepts [Contents][Index]
Many functions that perform file operations accept either open or closed streams as arguments; see Section 21.1.3 (Stream Arguments to Standardized Functions).
Of these, the functions in the next figure treat open and closed streams differently.
|
Figure 20.2: File Functions that Treat Open and Closed Streams Differently
Since treatment of open streams by the file system may vary considerably between implementations, however, a closed stream might be the most reliable kind of argument for some of these functions—in particular, those in the next figure. For example, in some file systems, open files are written under temporary names and not renamed until closed and/or are held invisible until closed. In general, any code that is intended to be portable should use such functions carefully.
|
Figure 20.3: File Functions where Closed Streams Might Work Best
Previous: File Operations on Open and Closed Streams, Up: File System Concepts [Contents][Index]
Many file systems permit more than one filename to designate a particular file.
Even where multiple names are possible, most file systems have a convention for generating a canonical filename in such situations. Such a canonical filename (or the pathname representing such a filename) is called a truename.
The truename of a file may differ from other filenames for the file because of symbolic links, version numbers, logical device translations in the file system, logical pathname translations within Common Lisp, or other artifacts of the file system.
The truename for a file is often, but not necessarily, unique for each file. For instance, a Unix file with multiple hard links could have several truenames.
For example, a DEC TOPS-20 system with files PS:<JOE>FOO.TXT.1
and PS:<JOE>FOO.TXT.2 might permit the second file to be referred
to as PS:<JOE>FOO.TXT.0, since the “.0” notation denotes “newest”
version of several files.
In the same file system, a “logical device” “JOE:” might be
taken to refer to PS:<JOE>” and so the names JOE:FOO.TXT.2 or
JOE:FOO.TXT.0 might refer to PS:<JOE>FOO.TXT.2.
In all of these cases, the truename of the file would probably be
PS:<JOE>FOO.TXT.2.
If a file is a symbolic link to another file (in a file system permitting such a thing), it is conventional for the truename to be the canonical name of the file after any symbolic links have been followed; that is, it is the canonical name of the file whose contents would become available if an input stream to that file were opened.
In the case of a file still being created (that is, of an output
stream open to such a file), the exact truename of the file
might not be known until the stream is closed. In this case,
the function truename might return different values for such a stream
before and after it was closed. In fact, before it is closed, the name returned
might not even be a valid name in the file system—for example, while a
file is being written, it might have version :newest and might only take on
a specific numeric value later when the file is closed even in a file system
where all files have numeric versions.
Next: probe-file, Previous: File System Concepts, Up: Files [Contents][Index]
pathspec—a pathname designator, which may contain wild components.
pathnames—a list of physical pathnames.
Determines which, if any, files that are present in the file system have names matching pathspec, and returns a fresh list of pathnames corresponding to the truenames of those files.
An implementation may be extended to accept
implementation-defined keyword arguments to directory.
The host computer’s file system.
If the attempt to obtain a directory listing is not successful,
an error of type file-error is signaled.
pathname (System Class), logical-pathname (System Class), ensure-directories-exist, Section 20.1 (File System Concepts), Section 21.1.1.1.2 (Open and Closed Streams), Section 19.1.2 (Pathnames as Filenames)
If the pathspec is not wild, the resulting list will contain either zero or one elements.
Common Lisp specifies “&key” in the argument list to directory
even though no standardized keyword arguments to directory are defined.
“:allow-other-keys t”
may be used in conforming programs in order to quietly ignore any
additional keywords which are passed by the program but not supported
by the implementation.
Next: ensure-directories-exist, Previous: directory, Up: Files [Contents][Index]
pathspec—a pathname designator.
truename—a physical pathname or nil.
probe-file tests whether a file exists.
probe-file returns false if there is no file named pathspec,
and otherwise returns the truename of pathspec.
If the pathspec designator is an open stream,
then probe-file produces the truename of its associated file.
If pathspec is a stream, whether open or closed,
it is coerced to a pathname as if by the function pathname.
The host computer’s file system.
An error of type file-error is signaled if pathspec is wild.
An error of type file-error is signaled
if the file system cannot perform the requested operation.
truename, open, ensure-directories-exist, pathname (System Class), logical-pathname (System Class), Section 20.1 (File System Concepts), Section 21.1.1.1.2 (Open and Closed Streams), Section 19.1.2 (Pathnames as Filenames)
Next: truename, Previous: probe-file, Up: Files [Contents][Index]
pathspec—a pathname designator.
verbose—a generalized boolean.
created—a generalized boolean.
Tests whether the directories containing the specified file actually exist, and attempts to create them if they do not.
If the containing directories do not exist and if verbose is true, then the implementation is permitted (but not required) to perform output to standard output saying what directories were created. If the containing directories exist, or if verbose is false, this function performs no output.
The primary value is the given pathspec so that this operation can be straightforwardly composed with other file manipulation expressions. The secondary value, created, is true if any directories were created.
The host computer’s file system.
An error of type file-error is signaled if the host, device, or directory
part of pathspec is wild.
If the directory creation attempt is not successful,
an error of type file-error is signaled;
if this occurs,
it might be the case that none, some, or all
of the requested creations have actually occurred
within the file system.
probe-file, open, Section 19.1.2 (Pathnames as Filenames)
Next: file-author, Previous: ensure-directories-exist, Up: Files [Contents][Index]
filespec—a pathname designator.
truename—a physical pathname.
truename tries to find the file indicated by
filespec and returns its truename.
If the filespec designator is an open stream,
its associated file is used.
If filespec is a stream,
truename can be used whether the stream
is open or closed. It is permissible for truename
to return more specific information after the stream
is closed than when the stream was open.
If filespec is a pathname
it represents the name used to open the file. This may be, but is
not required to be, the actual name of the file.
;; An example involving version numbers. Note that the precise nature of
;; the truename is implementation-dependent while the file is still open.
(with-open-file (stream ">vistor>test.text.newest")
(values (pathname stream)
(truename stream)))
→ #P"S:>vistor>test.text.newest", #P"S:>vistor>test.text.1"
or→ #P"S:>vistor>test.text.newest", #P"S:>vistor>test.text.newest"
or→ #P"S:>vistor>test.text.newest", #P"S:>vistor>_temp_._temp_.1"
;; In this case, the file is closed when the truename is tried, so the
;; truename information is reliable.
(with-open-file (stream ">vistor>test.text.newest")
(close stream)
(values (pathname stream)
(truename stream)))
→ #P"S:>vistor>test.text.newest", #P"S:>vistor>test.text.1"
;; An example involving TOP-20's implementation-dependent concept
;; of logical devices -- in this case, "DOC:" is shorthand for
;; "PS:<DOCUMENTATION>" ...
(with-open-file (stream "CMUC::DOC:DUMPER.HLP")
(values (pathname stream)
(truename stream)))
→ #P"CMUC::DOC:DUMPER.HLP", #P"CMUC::PS:<DOCUMENTATION>DUMPER.HLP.13"
An error of type file-error is signaled if an appropriate file
cannot be located within the file system for the given filespec,
or if the file system cannot perform the requested operation.
An error of type file-error is signaled if pathname is wild.
pathname (System Class), logical-pathname (System Class), Section 20.1 (File System Concepts), Section 19.1.2 (Pathnames as Filenames)
truename may be used to account for any filename translations
performed by the file system.
Next: file-write-date, Previous: truename, Up: Files [Contents][Index]
pathspec—a pathname designator.
author—a string or nil.
Returns a string naming the author of the file specified by pathspec,
or nil if the author’s name cannot be determined.
(with-open-file (stream ">relativity>general.text")
(file-author s))
→ "albert"
The host computer’s file system.
Other users of the file named by pathspec.
An error of type file-error is signaled if pathspec is wild.
An error of type file-error is signaled
if the file system cannot perform the requested operation.
pathname (System Class), logical-pathname (System Class), Section 20.1 (File System Concepts), Section 19.1.2 (Pathnames as Filenames)
Next: rename-file, Previous: file-author, Up: Files [Contents][Index]
pathspec—a pathname designator.
date—a universal time or nil.
Returns a universal time representing the time at which the file
specified by pathspec was last written (or created),
or returns nil if such a time cannot be determined.
(with-open-file (s "noel.text"
:direction :output :if-exists :error)
(format s "~&Dear Santa,~2%I was good this year. ~
Please leave lots of toys.~2%Love, Sue~
~2%attachments: milk, cookies~%")
(truename s))
→ #P"CUPID:/susan/noel.text"
(with-open-file (s "noel.text")
(file-write-date s))
→ 2902600800
The host computer’s file system.
An error of type file-error is signaled if pathspec is wild.
An error of type file-error is signaled
if the file system cannot perform the requested operation.
Section 25.1.4.2 (Universal Time), Section 19.1.2 (Pathnames as Filenames)
Next: delete-file, Previous: file-write-date, Up: Files [Contents][Index]
filespec—a pathname designator.
new-name—a pathname designator other than a stream.
defaulted-new-name—a pathname
old-truename—a physical pathname.
new-truename—a physical pathname.
rename-file modifies the file system in such a way
that the file indicated by filespec is renamed to
defaulted-new-name.
It is an error to specify a filename containing a wild component,
for filespec to contain a nil component where the file system does
not permit a nil component, or for the result of defaulting missing
components of new-name from filespec to contain a nil component
where the file system does not permit a nil component.
If new-name is a logical pathname,
rename-file returns a logical pathname as its primary value.
rename-file
returns three values if successful. The primary value, defaulted-new-name,
is the resulting name which is composed of
new-name with any missing components filled in by performing
a merge-pathnames operation using filespec as the defaults.
The secondary value, old-truename,
is the truename of the file before it was renamed.
The tertiary value, new-truename,
is the truename of the file after it was renamed.
If the filespec designator is an open stream, then the stream itself and the file associated with it are affected (if the file system permits).
;; An example involving logical pathnames.
(with-open-file (stream "sys:chemistry;lead.text"
:direction :output :if-exists :error)
(princ "eureka" stream)
(values (pathname stream) (truename stream)))
→ #P"SYS:CHEMISTRY;LEAD.TEXT.NEWEST", #P"Q:>sys>chem>lead.text.1"
(rename-file "sys:chemistry;lead.text" "gold.text")
→ #P"SYS:CHEMISTRY;GOLD.TEXT.NEWEST",
#P"Q:>sys>chem>lead.text.1",
#P"Q:>sys>chem>gold.text.1"
If the renaming operation is not successful, an error of type file-error is signaled.
An error of type file-error might be signaled if filespec is wild.
truename, pathname (System Class), logical-pathname (System Class), Section 20.1 (File System Concepts), Section 19.1.2 (Pathnames as Filenames)
Next: file-error, Previous: rename-file, Up: Files [Contents][Index]
tfilespec—a pathname designator.
Deletes the file specified by filespec.
If the filespec designator is an open stream, then filespec and the file associated with it are affected (if the file system permits), in which case filespec might be closed immediately, and the deletion might be immediate or delayed until filespec is explicitly closed, depending on the requirements of the file system.
It is implementation-dependent whether an attempt to delete a nonexistent file is considered to be successful.
delete-file returns true if it succeeds,
or signals an error of type file-error if it does not.
The consequences are undefined
if filespec has a wild component,
or if filespec has a nil component
and the file system does not permit a nil component.
(with-open-file (s "delete-me.text" :direction :output :if-exists :error)) → NIL (setq p (probe-file "delete-me.text")) → #P"R:>fred>delete-me.text.1" (delete-file p) → T (probe-file "delete-me.text") → false (with-open-file (s "delete-me.text" :direction :output :if-exists :error) (delete-file s)) → T (probe-file "delete-me.text") → false
If the deletion operation is not successful, an error of type file-error is signaled.
An error of type file-error might be signaled if filespec is wild.
pathname (System Class), logical-pathname (System Class), Section 20.1 (File System Concepts), Section 19.1.2 (Pathnames as Filenames)
Next: file-error-pathname, Previous: delete-file, Up: Files [Contents][Index]
file-error,
error,
serious-condition,
condition,
t
The type file-error consists of error conditions that occur during
an attempt to open or close a file, or during some low-level transactions
with a file system. The “offending pathname” is initialized by
the :pathname initialization argument to make-condition, and is accessed
by the function file-error-pathname.
file-error-pathname, open, probe-file, directory, ensure-directories-exist
Previous: file-error, Up: Files [Contents][Index]
condition—a condition of type file-error.
pathspec—a pathname designator.
Returns the “offending pathname” of a condition of type file-error.
file-error, Chapter 9 (Conditions)
Previous: file-error, Up: Files [Contents][Index]