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These procedures allow querying and setting file system attributes (such as owner, permissions, sizes and types of files); deleting, copying, renaming and linking files; creating and removing directories and querying their contents; syncing the file system and creating special files.
Test accessibility of a file under the real UID and GID of the calling
process. The return is #t if path exists and the
permissions requested by how are all allowed, or #f if
not.
how is an integer which is one of the following values, or a
bitwise-OR (logior) of multiple values.
Test for read permission.
Test for write permission.
Test for execute permission.
Test for existence of the file. This is implied by each of the other tests, so there’s no need to combine it with them.
It’s important to note that access? does not simply indicate
what will happen on attempting to read or write a file. In normal
circumstances it does, but in a set-UID or set-GID program it doesn’t
because access? tests the real ID, whereas an open or execute
attempt uses the effective ID.
A program which will never run set-UID/GID can ignore the difference
between real and effective IDs, but for maximum generality, especially
in library functions, it’s best not to use access? to predict
the result of an open or execute, instead simply attempt that and
catch any exception.
The main use for access? is to let a set-UID/GID program
determine what the invoking user would have been allowed to do,
without the greater (or perhaps lesser) privileges afforded by the
effective ID. For more on this, see Testing File Access in The GNU C Library Reference Manual.
Return an object containing various information about the file
determined by object. object can be a string containing
a file name or a port or integer file descriptor which is open
on a file (in which case fstat is used as the underlying
system call).
If the optional exception_on_error argument is true, which
is the default, an exception will be raised if the underlying
system call returns an error, for example if the file is not
found or is not readable. Otherwise, an error will cause
stat to return #f.
The object returned by stat can be passed as a single
parameter to the following procedures, all of which return
integers:
The device number containing the file.
The file serial number, which distinguishes this file from all other files on the same device.
The mode of the file. This is an integer which incorporates file type
information and file permission bits. See also stat:type and
stat:perms below.
The number of hard links to the file.
The user ID of the file’s owner.
The group ID of the file.
Device ID; this entry is defined only for character or block special
files. On some systems this field is not available at all, in which
case stat:rdev returns #f.
The size of a regular file in bytes.
The last access time for the file, in seconds.
The last modification time for the file, in seconds.
The last modification time for the attributes of the file, in seconds.
The fractional part of a file’s access, modification, or attribute modification time, in nanoseconds. Nanosecond timestamps are only available on some operating systems and file systems. If Guile cannot retrieve nanosecond-level timestamps for a file, these fields will be set to 0.
The optimal block size for reading or writing the file, in bytes. On
some systems this field is not available, in which case
stat:blksize returns a sensible suggested block size.
The amount of disk space that the file occupies measured in units of
512 byte blocks. On some systems this field is not available, in
which case stat:blocks returns #f.
In addition, the following procedures return the information
from stat:mode in a more convenient form:
A symbol representing the type of file. Possible values are ‘regular’, ‘directory’, ‘symlink’, ‘block-special’, ‘char-special’, ‘fifo’, ‘socket’, and ‘unknown’.
An integer representing the access permission bits.
Similar to stat, but does not follow symbolic links, i.e.,
it will return information about a symbolic link itself, not the
file it points to. path must be a string.
Return the value of the symbolic link named by path (a string), i.e., the file that the link points to.
Change the ownership and group of the file referred to by object
to the integer values owner and group. object can
be a string containing a file name or, if the platform supports
fchown (see File Owner in The GNU C Library Reference
Manual), a port or integer file descriptor which is open on the file.
The return value is unspecified.
If object is a symbolic link, either the
ownership of the link or the ownership of the referenced file will be
changed depending on the operating system (lchown is
unsupported at present). If owner or group is specified
as -1, then that ID is not changed.
Changes the permissions of the file referred to by object.
object can be a string containing a file name or a port or integer file
descriptor which is open on a file (in which case fchmod is used
as the underlying system call).
mode specifies
the new permissions as a decimal number, e.g., (chmod "foo" #o755).
The return value is unspecified.
utime sets the access and modification times for the
file named by pathname. If actime or modtime is
not supplied, then the current time is used. actime and
modtime must be integer time values as returned by the
current-time procedure.
The optional actimens and modtimens are nanoseconds to add actime and modtime. Nanosecond precision is only supported on some combinations of file systems and operating systems.
(utime "foo" (- (current-time) 3600))
will set the access time to one hour in the past and the modification time to the current time.
Last, flags may be either 0 or the
AT_SYMLINK_NOFOLLOW constant, to set the time of
pathname even if it is a symbolic link.
Deletes (or “unlinks”) the file whose path is specified by str.
Copy the file specified by oldfile to newfile. The return value is unspecified.
Send count bytes from in to out, both of which must be either open file ports or file descriptors. When offset is omitted, start reading from in’s current position; otherwise, start reading at offset. Return the number of bytes actually sent.
When in is a port, it is often preferable to specify offset, because in’s offset as a port may be different from the offset of its underlying file descriptor.
On systems that support it, such as GNU/Linux, this procedure uses the
sendfile libc function, which usually corresponds to a system
call. This is faster than doing a series of read and
write system calls. A typical application is to send a file over
a socket.
In some cases, the sendfile libc function may return
EINVAL or ENOSYS. In that case, Guile’s sendfile
procedure automatically falls back to doing a series of read and
write calls.
In other cases, the libc function may send fewer bytes than
count—for instance because out is a slow or limited
device, such as a pipe. When that happens, Guile’s sendfile
automatically retries until exactly count bytes were sent or an
error occurs.
Renames the file specified by oldname to newname. The return value is unspecified.
Creates a new name newpath in the file system for the file named by oldpath. If oldpath is a symbolic link, the link may or may not be followed depending on the system.
Create a symbolic link named newpath with the value (i.e., pointing to) oldpath. The return value is unspecified.
Create a new directory named by path. If mode is omitted
then the permissions of the directory are set to #o777
masked with the current umask (see umask).
Otherwise they are set to the value specified with mode.
The return value is unspecified.
Remove the existing directory named by path. The directory must be empty for this to succeed. The return value is unspecified.
Open the directory specified by dirname and return a directory stream.
Before using this and the procedures below, make sure to see the higher-level procedures for directory traversal that are available (see File Tree Walk).
Return a boolean indicating whether object is a directory
stream as returned by opendir.
Return (as a string) the next directory entry from the directory stream stream. If there is no remaining entry to be read then the end of file object is returned.
Reset the directory port stream so that the next call to
readdir will return the first directory entry.
Close the directory stream stream. The return value is unspecified.
Here is an example showing how to display all the entries in a directory:
(define dir (opendir "/usr/lib"))
(do ((entry (readdir dir) (readdir dir)))
((eof-object? entry))
(display entry)(newline))
(closedir dir)
Flush the operating system disk buffers. The return value is unspecified.
Creates a new special file, such as a file corresponding to a device. path specifies the name of the file. type should be one of the following symbols: ‘regular’, ‘directory’, ‘symlink’, ‘block-special’, ‘char-special’, ‘fifo’, or ‘socket’. perms (an integer) specifies the file permissions. dev (an integer) specifies which device the special file refers to. Its exact interpretation depends on the kind of special file being created.
E.g.,
(mknod "/dev/fd0" 'block-special #o660 (+ (* 2 256) 2))
The return value is unspecified.
Return an auto-generated name of a temporary file, a file which doesn’t already exist. The name includes a path, it’s usually in /tmp but that’s system dependent.
Care must be taken when using tmpnam. In between choosing the
name and creating the file another program might use that name, or an
attacker might even make it a symlink pointing at something important
and causing you to overwrite that.
The safe way is to create the file using open with
O_EXCL to avoid any overwriting. A loop can try again with
another name if the file exists (error EEXIST).
mkstemp! below does that.
Create a new unique file in the file system and return a new buffered port open for reading and writing to the file.
tmpl is a string specifying where the file should be created: it
must end with ‘XXXXXX’ and those ‘X’s will be changed in the
string to return the name of the file. (port-filename on the
port also gives the name.)
POSIX doesn’t specify the permissions mode of the file, on GNU and
most systems it’s #o600. An application can use chmod
to relax that if desired. For example #o666 less umask,
which is usual for ordinary file creation,
(let ((port (mkstemp! (string-copy "/tmp/myfile-XXXXXX")))) (chmod port (logand #o666 (lognot (umask)))) ...)
The optional mode argument specifies a mode with which to open the
new file, as a string in the same format that open-file takes.
It defaults to "w+".
Return an input/output port to a unique temporary file
named using the path prefix P_tmpdir defined in
stdio.h.
The file is automatically deleted when the port is closed
or the program terminates.
Return the directory name component of the file name
filename. If filename does not contain a directory
component, . is returned.
Return the base name of the file name filename. The base name is the file name without any directory components. If suffix is provided, and is equal to the end of basename, it is removed also.
(basename "/tmp/test.xml" ".xml") ⇒ "test"
Return #t if the file named filename exists, #f if
not.
Many operating systems, such as GNU, use / (forward slash) to
separate the components of a file name; any file name starting with
/ is considered an absolute file name. These conventions
are specified by the POSIX Base Definitions, which refer to conforming
file names as “pathnames”. Some operating systems use a different
convention; in particular, Windows uses \ (backslash) as the file
name separator, and also has the notion of volume names like
C:\ for absolute file names. The following procedures and
variables provide support for portable file name manipulations.
Return either posix or windows, depending on
what kind of system this Guile is running on.
Return true if character c is a file name separator on the host platform.
Return true if file-name denotes an absolute file name on the host platform.
The preferred file name separator.
Note that on MinGW builds for Windows, both / and \ are
valid separators. Thus, programs should not assume that
file-name-separator-string is the only file name
separator—e.g., when extracting the components of a file name.
Next: User Information, Previous: Ports and File Descriptors, Up: POSIX [Contents][Index]