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These functions test for permission to access a file in specific ways.
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
.
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 |
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.
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 |
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 or the file name of a
file which is a directory.
Example: after the following,
(file-accessible-directory-p "/foo") => nil |
we can deduce that any attempt to read a file in `/foo/' will give an error.
nil
. However, if the open fails, it signals an error
using string as the error message text.
t
if deleting the file filename and
then creating it anew would keep the file's owner unchanged.
t
if the file filename1 is
newer than file filename2. If filename1 does not
exist, it returns nil
. If filename2 does not exist,
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 |
You can use file-attributes
to get a file's last modification
time as a list of two numbers. See section 25.6.4 Other Information about Files.
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