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.

primitive: access? path how

Returns #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.

primitive: stat obj

Returns 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:

stat:dev

The device containing the file.

stat:ino

The file serial number, which distinguishes this file from all other files on the same device.

stat:mode

The mode of the file. This includes file type information and the file permission bits. See stat:type and stat:perms below.

stat:nlink

The number of hard links to the file.

stat:uid

The user ID of the file's owner.

stat:gid

The group ID of the file.

stat:rdev

Device ID; this entry is defined only for character or block special files.

stat:size

The size of a regular file in bytes.

stat:atime

The last access time for the file.

stat:mtime

The last modification time for the file.

stat:ctime

The last modification time for the attributes of the file.

stat:blksize

The optimal block size for reading or writing the file, in bytes.

stat:blocks

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:

stat:type

A symbol representing the type of file. Possible values are regular, directory, symlink, block-special, char-special, fifo, socket and unknown

stat:perms

An integer representing the access permission bits.

primitive: lstat path

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.

primitive: readlink path

Returns the value of the symbolic link named by path (a string), i.e., the file that the link points to.

primitive: chown obj owner group

Change the ownership and group of the file referred to by obj to the integer userid values owner and group. obj can be a string containing a file name or a port or integer file descriptor which is open on the file (in which case fchown is used as the underlying system call). The return value is unspecified.

If obj 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.

primitive: chmod obj 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.

primitive: utime path [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.

E.g.,

(utime "foo" (- (current-time) 3600))

will set the access time to one hour in the past and the modification time to the current time.

primitive: delete-file path

Deletes (or "unlinks") the file specified by path.

primitive: copy-file path-from path-to

Copy the file specified by path-from to path-to. The return value is unspecified.

primitive: rename-file path-from path-to

Renames the file specified by path-from to path-to. The return value is unspecified.

primitive: truncate-file obj size

Truncates the file referred to by obj to at most size bytes. obj can be a string containing a file name or an integer file descriptor or port open for output on the file. The underlying system calls are truncate and ftruncate.

The return value is unspecified.

primitive: link path-from path-to

Creates a new name path-to in the file system for the file named by path-from. If path-from is a symbolic link, the link may or may not be followed depending on the system.

primitive: symlink path-from path-to

Create a symbolic link named path-to with the value (i.e., pointing to) path-from. The return value is unspecified.

primitive: 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.

primitive: rmdir path

Remove the existing directory named by path. The directory must be empty for this to succeed. The return value is unspecified.

primitive: opendir path

Open the directory specified by path and return a directory port.

primitive: readdir port

Return (as a string) the next directory entry from the directory port port. If there is no remaining entry to be read then the end of file object is returned.

primitive: rewinddir port

Reset the directory port port so that the next call to readdir will return the first directory entry.

primitive: closedir port

Close the directory port port. The return value is unspecified.

primitive: sync

Flush the operating system disk buffers. The return value is unspecified.

primitive: 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.

E.g.,

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

The return value is unspecified.

primitive: tmpnam

Create a new file in the file system with a unique name. The return value is the name of the new file. This function is implemented with the tmpnam function in the system libraries.

Go to the first, previous, next, last section, table of contents.