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38.3 File System

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.

Scheme Procedure: access? path how
C Function: scm_access (path, how)
Return #t if path corresponds to an existing file and the current process has the type of access specified by how, otherwise #f. how should be specified using the values of the variables listed below. Multiple values can be combined using a bitwise or, in which case #t will only be returned if all accesses are granted.

Permissions are checked using the real id of the current process, not the effective id, although it's the effective id which determines whether the access would actually be granted.

Variable: R_OK
test for read permission.
Variable: W_OK
test for write permission.
Variable: X_OK
test for execute permission.
Variable: F_OK
test for existence of the file.

Scheme Procedure: stat object
C Function: scm_stat (object)
Return an object containing various information about the file determined by obj. obj 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).

The object returned by stat can be passed as a single parameter to the following procedures, all of which return integers:

The device 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 includes file type information and the file permission bits. See 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.
The size of a regular file in bytes.
The last access time for the file.
The last modification time for the file.
The last modification time for the attributes of the file.
The optimal block size for reading or writing the file, in bytes.
The amount of disk space that the file occupies measured in units of 512 byte blocks.

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.

Scheme Procedure: lstat str
C Function: scm_lstat (str)
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.

Scheme Procedure: readlink path
C Function: scm_readlink (path)
Return the value of the symbolic link named by path (a string), i.e., the file that the link points to.

Scheme Procedure: chown object owner group
C Function: scm_chown (object, owner, group)
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, 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.

Scheme Procedure: chmod object mode
C Function: scm_chmod (object, mode)
Changes the permissions of the file referred to by obj. obj 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.

Scheme Procedure: utime pathname [actime [modtime]]
C Function: scm_utime (pathname, actime, modtime)
utime sets the access and modification times for the file named by path. 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.
(utime "foo" (- (current-time) 3600))
will set the access time to one hour in the past and the modification time to the current time.

Scheme Procedure: delete-file str
C Function: scm_delete_file (str)
Deletes (or "unlinks") the file specified by path.

Scheme Procedure: copy-file oldfile newfile
C Function: scm_copy_file (oldfile, newfile)
Copy the file specified by path-from to path-to. The return value is unspecified.

Scheme Procedure: rename-file oldname newname
C Function: scm_rename (oldname, newname)
Renames the file specified by oldname to newname. The return value is unspecified.

Scheme Procedure: link oldpath newpath
C Function: scm_link (oldpath, newpath)
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.

Scheme Procedure: symlink oldpath newpath
C Function: scm_symlink (oldpath, newpath)
Create a symbolic link named path-to with the value (i.e., pointing to) path-from. The return value is unspecified.

Scheme Procedure: mkdir path [mode]
C Function: scm_mkdir (path, mode)
Create a new directory named by path. If mode is omitted then the permissions of the directory file are set using the current umask. Otherwise they are set to the decimal value specified with mode. The return value is unspecified.

Scheme Procedure: rmdir path
C Function: scm_rmdir (path)
Remove the existing directory named by path. The directory must be empty for this to succeed. The return value is unspecified.

Scheme Procedure: opendir dirname
C Function: scm_opendir (dirname)
Open the directory specified by path and return a directory stream.

Scheme Procedure: directory-stream? obj
C Function: scm_directory_stream_p (obj)
Return a boolean indicating whether object is a directory stream as returned by opendir.

Scheme Procedure: readdir port
C Function: scm_readdir (port)
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.

Scheme Procedure: rewinddir port
C Function: scm_rewinddir (port)
Reset the directory port stream so that the next call to readdir will return the first directory entry.

Scheme Procedure: closedir port
C Function: scm_closedir (port)
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)

Scheme Procedure: sync
C Function: scm_sync ()
Flush the operating system disk buffers. The return value is unspecified.

Scheme Procedure: mknod path type perms dev
C Function: scm_mknod (path, type, perms, dev)
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.

(mknod "/dev/fd0" 'block-special #o660 (+ (* 2 256) 2))

The return value is unspecified.

Scheme Procedure: tmpnam
C Function: scm_tmpnam ()
Return a name in the file system that does not match any existing file. However there is no guarantee that another process will not create the file after tmpnam is called. Care should be taken if opening the file, e.g., use the O_EXCL open flag or use mkstemp! instead.

Scheme Procedure: mkstemp! tmpl
C Function: scm_mkstemp (tmpl)
Create a new unique file in the file system and returns 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 will be changed in place to return the name of the temporary file.

Scheme Procedure: dirname filename
C Function: scm_dirname (filename)
Return the directory name component of the file name filename. If filename does not contain a directory component, . is returned.

Scheme Procedure: basename filename [suffix]
C Function: scm_basename (filename, suffix)
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"

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