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These functions test for permission to access a file in specific ways. Unless explicitly stated otherwise, they recursively follow symbolic links for their file name arguments, at all levels (at the level of the file itself and at all levels of parent directories).
This function returns t if a file named filename appears to
exist. This does not mean you can necessarily read the file, only that you
can find out its attributes. (On Unix and GNU/Linux, this is true if the
file exists and you have execute permission on the containing directories,
regardless of the protection of the file itself.)
If the file does not exist, or if fascist access control policies prevent
you from finding the attributes of the file, this function returns
nil.
Directories are files, so file-exists-p returns t when given a
directory name. However, symbolic links are treated specially;
file-exists-p returns t for a symbolic link name only if the
target file exists.
This function returns t if a file named filename exists and you
can read it. It returns nil otherwise.
(file-readable-p "files.texi")
⇒ t
(file-exists-p "/usr/spool/mqueue")
⇒ t
(file-readable-p "/usr/spool/mqueue")
⇒ nil
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This function returns t if a file named filename exists and you
can execute it. It returns nil otherwise. On Unix and GNU/Linux, if
the file is a directory, execute permission means you can check the
existence and attributes of files inside the directory, and open those files
if their modes permit.
This function returns t if the file filename can be written or
created by you, and nil otherwise. A file is writable if the file
exists and you can write it. It is creatable if it does not exist, but the
specified directory does exist and you can write in that directory.
In the third example below, ‘foo’ is not writable because the parent directory does not exist, even though the user could create such a directory.
(file-writable-p "~/foo")
⇒ t
(file-writable-p "/foo")
⇒ nil
(file-writable-p "~/no-such-dir/foo")
⇒ nil
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This function returns t if you have permission to open existing files
in the directory whose name as a file is dirname; otherwise (or if
there is no such directory), it returns nil. The value of
dirname may be either a directory name (such as ‘/foo/’) or the
file name of a file which is a directory (such as ‘/foo’, without the
final slash).
Example: after the following,
(file-accessible-directory-p "/foo")
⇒ nil
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we can deduce that any attempt to read a file in ‘/foo/’ will give an error.
This function opens file filename for reading, then closes it and
returns nil. However, if the open fails, it signals an error using
string as the error message text.
This function returns t if deleting the file filename and then
creating it anew would keep the file's owner unchanged. It also returns
t for nonexistent files.
If filename is a symbolic link, then, unlike the other functions
discussed here, file-ownership-preserved-p does not replace
filename with its target. However, it does recursively follow
symbolic links at all levels of parent directories.
This function returns t if the file filename1 is newer than
file filename2. If filename1 does not exist, it returns
nil. If filename1 does exist, but filename2 does not, it
returns t.
In the following example, assume that the file ‘aug-19’ was written on the 19th, ‘aug-20’ was written on the 20th, and the file ‘no-file’ doesn't exist at all.
(file-newer-than-file-p "aug-19" "aug-20")
⇒ nil
(file-newer-than-file-p "aug-20" "aug-19")
⇒ t
(file-newer-than-file-p "aug-19" "no-file")
⇒ t
(file-newer-than-file-p "no-file" "aug-19")
⇒ nil
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You can use file-attributes to get a file's last modification time as
a list of two numbers. Voir la section Other Information about Files.
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Ce document a été généré par Eric Reinbold le 13 Octobre 2007 en utilisant texi2html 1.78.