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Unit posix

This unit provides services as used on many UNIX-like systems. Note that the following definitions are not all available on non-UNIX systems like Windows. See below for Windows specific notes.

This unit uses the regex, scheduler, extras and utils units.

All errors related to failing file-operations will signal a condition of kind (exn i/o file).

Constants

File-control Commands

fcntl/dupfd constant
fcntl/getfd constant
fcntl/setfd constant
fcntl/getfl constant
fcntl/setfl constant

Operations used with file-control.

Standard I/O file-descriptors

fileno/stdin constant
fileno/stdout constant
fileno/stderr constant

Standard I/O file descriptor numbers, used with procedures such as open-input-file* which take file descriptors.

Open flags

open/rdonly constant
open/wronly constant
open/rdwr constant
open/read constant
open/write constant
open/creat constant
open/append constant
open/excl constant
open/noctty constant
open/nonblock constant
open/trunc constant
open/sync constant
open/fsync constant
open/binary constant
open/text constant

Open flags used with the file-open procedure. open/read is a convenience synonym for open/rdonly, as is open/write for open/wronly.

Permission bits

perm/irusr constant
perm/iwusr constant
perm/ixusr constant
perm/irgrp constant
perm/iwgrp constant
perm/ixgrp constant
perm/iroth constant
perm/iwoth constant
perm/ixoth constant
perm/irwxu constant
perm/irwxg constant
perm/irwxo constant
perm/isvtx constant
perm/isuid constant
perm/isgid constant

Permission bits used with, for example, file-open.

Directories

change-directory

(change-directory NAME) procedure

Changes the current working directory to NAME.

change-directory*

(change-directory* FD) procedure

Changes the current working directory to the one represented by the file-descriptor FD, which should be an exact integer.

current-directory

(current-directory [DIR]) procedure

Returns the name of the current working directory. If the optional argument DIR is given, then (current-directory DIR) is equivalent to (change-directory DIR).

create-directory

(create-directory NAME #!optional PARENTS?) procedure

Creates a directory with the pathname NAME. If the PARENTS? argument is given and not false, any nonexistent parent directories are also created.

Notice that if NAME exists, create-directory won't try to create it and will return NAME (i.e., it won't raise an error when given a NAME that already exists).

delete-directory

(delete-directory NAME [RECURSIVE]) procedure

Deletes the directory with the pathname NAME. If RECURSIVE is not given or false, then the directory has to be empty.

directory

(directory [PATHNAME [SHOW-DOTFILES?]]) procedure

Returns a list with all files that are contained in the directory with the name PATHNAME (which defaults to the value of (current-directory)). Files beginning with . are included only if SHOW-DOTFILES? is given and not #f.

directory?

(directory? FILE) procedure

Returns #t if FILE designates directory. Otherwise, it returns #f. FILE may be a pathname or a file-descriptor.

glob

(glob PATTERN1 ...) procedure

Returns a list of the pathnames of all existing files matching PATTERN1 ..., which should be strings containing the usual file-patterns (with * matching zero or more characters and ? matching zero or one character).

set-root-directory!

(set-root-directory! STRING) procedure

Sets the root directory for the current process to the path given in STRING (using the chroot function). If the current process has no root permissions, the operation will fail.

Pipes

call-with-input-pipe

call-with-output-pipe

(call-with-input-pipe CMDLINE PROC [MODE]) procedure
(call-with-output-pipe CMDLINE PROC [MODE]) procedure

Call PROC with a single argument: a input- or output port for a pipe connected to the subprocess named in CMDLINE. If PROC returns normally, the pipe is closed and any result values are returned.

close-input-pipe

close-output-pipe

(close-input-pipe PORT) procedure
(close-output-pipe PORT) procedure

Closes the pipe given in PORT and waits until the connected subprocess finishes. The exit-status code of the invoked process is returned.

create-pipe

(create-pipe) procedure

The fundamental pipe-creation operator. Calls the C function pipe() and returns 2 values: the file-descriptors of the input- and output-ends of the pipe.

open-input-pipe

(open-input-pipe CMDLINE [MODE]) procedure

Spawns a subprocess with the command-line string CMDLINE and returns a port, from which the output of the process can be read. If MODE is specified, it should be the keyword #:text (the default) or #:binary.

open-output-pipe

(open-output-pipe CMDLINE [MODE]) procedure

Spawns a subprocess with the command-line string CMDLINE and returns a port. Anything written to that port is treated as the input for the process. If MODE is specified, it should be the keyword #:text (the default) or #:binary.

pipe/buf

This variable contains the maximal number of bytes that can be written atomically into a pipe or FIFO.

with-input-from-pipe

with-output-to-pipe

(with-input-from-pipe CMDLINE THUNK [MODE]) procedure
(with-output-to-pipe CMDLINE THUNK [MODE]) procedure

Temporarily set the value of current-input-port/current-output-port to a port for a pipe connected to the subprocess named in CMDLINE and call the procedure THUNK with no arguments. After THUNK returns normally the pipe is closed and the standard input-/output port is restored to its previous value and any result values are returned.

(with-output-to-pipe
  "gs -dNOPAUSE -sDEVICE=jpeg -dBATCH -sOutputFile=signballs.jpg -g600x600 -q -"
  (lambda ()
    (print #<<EOF
 %!IOPSC-1993 %%Creator: HAYAKAWA Takashi<xxxxxxxx@xx.xxxxxx.xx.xx>
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 H/A/copy(z&v4QX&93r9AxYQOZomQalxS2w!!O&vMYa43d6r93rMYvx2dca!D&cjSnjSnjjS3o!v&6A
 X&55SAxM1CD7AjYxTTd62rmxCnTdSST0g&12wECST!&!J0g&D1!&xM0!J0g!l&544dC2Ac96ra!m&3A
 F&&vGoGSnCT0g&wDmlvGoS8wpn6wpS2wTCpS1Sd7ov7Uk7o4Qkdw!&Mvlx1S7oZES3w!J!J!Q&7185d
 Z&lx1CS9d9nE4!k&X&MY7!&1!J!x&jdnjdS3odS!N&mmx1C2wEc!G&150Nx4!n&2o!j&43r!U&0777d
 ]&2AY2A776ddT4oS3oSnMVC00VV0RRR45E42063rNz&v7UX&UOzF!F!J![&44ETCnVn!a&1CDN!Y&0M
 V1c&j2AYdjmMdjjd!o&1r!M){( )T 0 4 3 r put T(/)g{T(9)g{cvn}{cvi}J}{($)g[]J}J
 cvx}forall/moveto/p/floor/w/div/S/add 29 H[{[{]setgray fill}for Y}for showpage
 EOF
 ) ) )

Fifos

create-fifo

(create-fifo FILENAME [MODE]) procedure

Creates a FIFO with the name FILENAME and the permission bits MODE, which defaults to

 (+ perm/irwxu perm/irwxg perm/irwxo)

fifo?

(fifo? FILE) procedure

Returns #t if FILE names a FIFO. FILE may be a filename or a file-descriptor.

File descriptors and low-level I/O

duplicate-fileno

(duplicate-fileno OLD [NEW]) procedure

If NEW is given, then the file-descriptor NEW is opened to access the file with the file-descriptor OLD. Otherwise a fresh file-descriptor accessing the same file as OLD is returned.

file-close

(file-close FILENO) procedure

Closes the input/output file with the file-descriptor FILENO.

file-open

(file-open FILENAME FLAGS [MODE]) procedure

Opens the file specified with the string FILENAME and open-flags FLAGS using the C function open(2). On success a file-descriptor for the opened file is returned.

FLAGS is a bitmask of open/... values ored together using bitwise-ior (or simply added together). You must provide exactly one of the access flags open/rdonly, open/wronly, or open/rdwr. Additionally, you may provide zero or more creation flags (open/creat, open/excl, open/trunc, and open/noctty) and status flags (the remaining open/... values). For example, to open a possibly new output file for appending:

(file-open "/tmp/hen.txt" (+ open/wronly open/append open/creat))

The optional MODE should be a bitmask composed of one or more permission values like perm/irusr and is only relevant when a new file is created. The default mode is perm/irwxu | perm/irgrp | perm/iroth.

file-mkstemp

(file-mkstemp TEMPLATE-FILENAME) procedure

Create a file based on the given TEMPLATE-FILENAME, in which the six last characters must be XXXXXX. These will be replaced with a string that makes the filename unique. The file descriptor of the created file and the generated filename is returned. See the mkstemp(3) manual page for details on how this function works. The template string given is not modified.

Example usage:

 (let-values (((fd temp-path) (file-mkstemp "/tmp/mytemporary.XXXXXX")))
  (let ((temp-port (open-output-file* fd)))
    (format temp-port "This file is ~A.~%" temp-path)
    (close-output-port temp-port)))

file-read

(file-read FILENO SIZE [BUFFER]) procedure

Reads SIZE bytes from the file with the file-descriptor FILENO. If a string or bytevector is passed in the optional argument BUFFER, then this string will be destructively modified to contain the read data. This procedure returns a list with two values: the buffer containing the data and the number of bytes read.

file-select

(file-select READFDLIST WRITEFDLIST [TIMEOUT]) procedure

Waits until any of the file-descriptors given in the lists READFDLIST and WRITEFDLIST is ready for input or output, respectively. If the optional argument TIMEOUT is given and not false, then it should specify the number of seconds after which the wait is to be aborted (the value may be a floating point number). This procedure returns two values: the lists of file-descriptors ready for input and output, respectively. READFDLIST and WRITEFDLIST may also by file-descriptors instead of lists. In this case the returned values are booleans indicating whether input/output is ready by #t or #f otherwise. You can also pass #f as READFDLIST or WRITEFDLIST argument, which is equivalent to ().

file-write

(file-write FILENO BUFFER [SIZE]) procedure

Writes the contents of the string or bytevector BUFFER into the file with the file-descriptor FILENO. If the optional argument SIZE is given, then only the specified number of bytes are written.

file-control

(file-control FILENO COMMAND [ARGUMENT]) procedure

Performs the fcntl operation COMMAND with the given FILENO and optional ARGUMENT. The return value is meaningful depending on the COMMAND.

open-input-file*

open-output-file*

(open-input-file* FILENO [OPENMODE]) procedure
(open-output-file* FILENO [OPENMODE]) procedure

Opens file for the file-descriptor FILENO for input or output and returns a port. FILENO should be a positive exact integer. OPENMODE specifies an additional mode for opening the file (currently only the keyword #:append is supported, which opens an output-file for appending).

port->fileno

(port->fileno PORT) procedure

If PORT is a file- or tcp-port, then a file-descriptor is returned for this port. Otherwise an error is signaled.

Retrieving file attributes

file-access-time

file-change-time

file-modification-time

(file-access-time FILE) procedure
(file-change-time FILE) procedure
(file-modification-time FILE) procedure
(set! (file-modification-time FILE) SECONDS) procedure

Returns time (in seconds) of the last access, modification or change of FILE. FILE may be a filename or a file-descriptor. If the file does not exist, an error is signaled.

(set! (file-modification-time FILE) SECONDS) sets the access- and modification time of FILE to SECONDS.

file-stat

(file-stat FILE [LINK]) procedure

Returns a 13-element vector with the following contents:

index value field notes
0 inode number st_ino
1 mode st_mode bitfield combining file permissions and file type
2 number of hard links st_nlink
3 UID of owner st_uid as with file-owner
4 GID of owner st_gid
5 size st_size as with file-size
6 access time st_atime as with file-access-time
7 change time st_ctime as with file-change-time
8 modification time st_mtime as with file-modification-time
9 parent device ID st_dev ID of device on which this file resides
10 device ID st_rdev device ID for special files (i.e. the raw major/minor number)
11 block size st_blksize
12 number of blocks allocated st_blocks

On Windows systems, the last 4 values are undefined.

By default, symbolic links are followed and the status of the referenced file is returned; however, if the optional argument LINK is given and not #f, the status of the link itself is returned.

Note that for very large files, the file-size value may be an inexact integer.

file-position

(file-position FILE) procedure

Returns the current file position of FILE, which should be a port or a file-descriptor.

file-size

(file-size FILE) procedure

Returns the size of the file designated by FILE. FILE may be a filename or a file-descriptor. If the file does not exist, an error is signaled. Note that for very large files, file-size may return an inexact integer.

regular-file?

(regular-file? FILENAME) procedure

Returns true, if FILENAME names a regular file (not a directory, socket, etc.) This operation follows symbolic links; use either symbolic-link? or file-type if you need to test for symlinks.

file-owner

(file-owner FILE) procedure

Returns the user-id of FILE. FILE may be a filename or a file-descriptor.

file-permissions

(file-permissions FILE) procedure

Returns the permission bits for FILE. You can test this value by performing bitwise operations on the result and the perm/... values. FILE may be a filename or a file-descriptor.

file-read-access?

file-write-access?

file-execute-access?

(file-read-access? FILENAME) procedure
(file-write-access? FILENAME) procedure
(file-execute-access? FILENAME) procedure

These procedures return #t if the current user has read, write or execute permissions on the file named FILENAME.

file-type

(file-type FILE [LINK [ERROR]]) procedure

Returns the file-type for FILE, which should be a filename or file-descriptor. If LINK is given and true, symbolic-links are not followed:

 regular-file
 directory
 fifo
 socket
 symbolic-link
 character-device
 block-device

Note that not all types are supported on every platform. If ERROR is given and true, file-type signals an error if the file does not exist.

character-device?

block-device?

socket?

(character-device? FILE) procedure
(block-device? FILE) procedure
(socket? FILE) procedure

These procedures return #t if FILE given is of the appropriate type. FILE may be a filename or a file-descriptor. Note that these operations follow symbolic links. If the file does not exist, #f is returned.

Changing file attributes

file-truncate

(file-truncate FILE OFFSET) procedure

Truncates the file FILE to the length OFFSET, which should be an integer. If the file-size is smaller or equal to OFFSET then nothing is done. FILE should be a filename or a file-descriptor.

set-file-position!

(set-file-position! FILE POSITION [WHENCE]) procedure
(set! (file-position FILE) POSITION) procedure

Sets the current read/write position of FILE to POSITION, which should be an exact integer. FILE should be a port or a file-descriptor. WHENCE specifies how the position is to interpreted and should be one of the values seek/set, seek/cur and seek/end. It defaults to seek/set.

Exceptions: (exn bounds), (exn i/o file)

change-file-mode

(change-file-mode FILENAME MODE) procedure

Changes the current file mode of the file named FILENAME to MODE using the chmod() system call. The perm/... variables contain the various permission bits and can be combinded with the bitwise-ior procedure.

change-file-owner

(change-file-owner FILENAME UID GID) procedure

Changes the owner information of the file named FILENAME to the user- and group-ids UID and GID (which should be exact integers) using the chown() system call.

file-creation-mode

(file-creation-mode [MODE]) procedure

Returns the initial file permissions used for newly created files (as with umask(2)). If MODE is supplied, the mode is changed to this value. You can set the mode by executing

 (set! (file-creation-mode) MODE)

or

 (file-creation-mode MODE)

where MODE is a bitwise combination of one or more of the perm/... flags.

Processes

current-process-id

(current-process-id) procedure

Returns the process ID of the current process.

parent-process-id

(parent-process-id) procedure

Returns the process ID of the parent of the current process.

process-group-id

(process-group-id PID) procedure

Returns the process group ID of the process specified by PID.

process-execute

(process-execute PATHNAME [ARGUMENT-LIST [ENVIRONMENT-LIST]]) procedure

Replaces the running process with a new process image from the program stored at PATHNAME, using the C library function execvp(3). If the optional argument ARGUMENT-LIST is given, then it should contain a list of strings which are passed as arguments to the subprocess. If the optional argument ENVIRONMENT-LIST is supplied, then the library function execve(2) is used, and the environment passed in ENVIRONMENT-LIST (which should be of the form ("<NAME>=<VALUE>" ...) is given to the invoked process. Note that execvp(3) respects the current setting of the PATH environment variable while execve(3) does not.

This procedure never returns; it either replaces the process with a new one or it raises an exception in case something went wrong executing the program.

process-fork

(process-fork [THUNK [KILLOTHERS?]]) procedure

Creates a new child process with the UNIX system call fork(). Returns either the PID of the child process or 0. If THUNK is given, then the child process calls it as a procedure with no arguments and terminates. If THUNK is given and the optional argument KILLOTHERS? is true, then kill all other existing threads in the child process, leaving only the current thread to run THUNK and terminate.

process-run

(process-run COMMANDLINE) procedure
(process-run COMMAND ARGUMENT-LIST) procedure

Creates a new child process. The PID of the new process is returned.

  • The single parameter version passes the COMMANDLINE to the system shell, so usual argument expansion can take place.
  • The multiple parameter version directly invokes the COMMAND with the ARGUMENT-LIST.

process-signal

(process-signal PID [SIGNAL]) procedure

Sends SIGNAL to the process with the id PID using the UNIX system call kill(). SIGNAL defaults to the value of the variable signal/term.

process-wait

(process-wait [PID [NOHANG]]) procedure

Suspends the current process until the child process with the id PID has terminated using the UNIX system call waitpid(). If PID is not given, then this procedure waits for any child process. If NOHANG is given and not #f then the current process is not suspended. This procedure returns three values:

  • PID or 0, if NOHANG is true and the child process has not terminated yet.
  • #t if the process exited normally or #f otherwise.
  • either the exit status, if the process terminated normally or the signal number that terminated/stopped the process.

Note that suspending the current process implies that all threads are suspended as well.

process

(process COMMANDLINE) procedure
(process COMMAND ARGUMENT-LIST [ENVIRONMENT-LIST]) procedure

Creates a subprocess and returns three values: an input port from which data written by the sub-process can be read, an output port from which any data written to will be received as input in the sub-process and the process-id of the started sub-process. Blocking reads and writes to or from the ports returned by process only block the current thread, not other threads executing concurrently.

Standard error for the subprocess is linked up to the current process's standard error (see process* if you want to reify its standard error into a separate port).

  • The single parameter version passes the string COMMANDLINE to the host-system's shell that is invoked as a subprocess.
  • The multiple parameter version directly invokes the COMMAND as a subprocess. The ARGUMENT-LIST is directly passed, as is ENVIRONMENT-LIST.

Not using the shell may be preferrable for security reasons.

Once both the input- and output ports are closed, an implicit waitpid(3) is done to wait for the subprocess to finish or to reap a subprocess that has terminated. If the subprocess has not finished, waiting for it will necessarily block all executing threads.

process*

(process* COMMANDLINE) procedure
(process* COMMAND ARGUMENT-LIST [ENVIRONMENT-LIST]) procedure

Like process but returns 4 values: an input port from which data written by the sub-process can be read, an output port from which any data written to will be received as input in the sub-process, the process-id of the started sub-process, and an input port from which data written by the sub-process to stderr can be read.

sleep

(sleep SECONDS) procedure

Puts the process to sleep for SECONDS. Returns either 0 if the time has completely elapsed, or the number of remaining seconds, if a signal occurred.

create-session

(create-session) procedure

Creates a new session if the calling process is not a process group leader and returns the session ID.

symbolic-link?

(symbolic-link? FILENAME) procedure

Returns true, if FILENAME names a symbolic link. If no such file exists, #f is returned. This operation does not follow symbolic links itself.

Creates a symbolic link with the filename NEWNAME that points to the file named OLDNAME.

Returns the filename to which the symbolic link FILENAME points. If CANONICALIZE is given and true, then symbolic links are resolved repeatedly until the result is not a link.

Creates a hard link from OLDNAME to NEWNAME (both strings).

Retrieving user & group information

current-user-id

(current-user-id) procedure
[setter] (set! (current-user-id) UID)

Get or set the real user-id of the current process. The procedure corresponds to the getuid and setuid C functions.

current-effective-user-id

(current-effective-user-id) procedure
[setter] (set! (current-effective-user-id) UID)

Get or set the effective user-id of the current process.

user-information

(user-information USER [AS-VECTOR]) procedure

If USER specifes a valid username (as a string) or user ID, then the user database is consulted and a list of 7 values are returned: the user-name, the encrypted password, the user ID, the group ID, a user-specific string, the home directory and the default shell. When AS-VECTOR is #t a vector of 7 elements is returned instead of a list. If no user with this name or id then #f is returned.

Note: on Android systems, the user-specific string is always "", since pw_gecos is not available in the C passwd struct on that platform.

current-group-id

(current-group-id) procedure
[setter] (set! (current-group-id) GID)

Get or set the real group-id of the current process.

current-effective-group-id

(current-effective-group-id) procedure
[setter] (set! (current-effective-group-id) GID)

Get or set the effective group-id of the current process. ID can be found, then #f is returned.

group-information

(group-information GROUP) procedure

If GROUP specifies a valid group-name or group-id, then this procedure returns a list of four values: the group-name, the encrypted group password, the group ID and a list of the names of all group members. If no group with the given name or ID exists, then #f is returned.

get-groups

(get-groups) procedure

Returns a list with the supplementary group IDs of the current user.

Changing user & group information

set-groups!

(set-groups! GIDLIST) procedure

Sets the supplementrary group IDs of the current user to the IDs given in the list GIDLIST.

Only the superuser may invoke this procedure.

initialize-groups

(initialize-groups USERNAME BASEGID) procedure

Sets the supplementrary group IDs of the current user to the IDs from the user with name USERNAME (a string), including BASEGID.

Only the superuser may invoke this procedure.

set-process-group-id!

(set-process-group-id! PID PGID) procedure
[setter] (set! (process-group-id PID) PGID)

Sets the process group ID of the process specifed by PID to PGID.

Record locking

file-lock

(file-lock PORT [START [LEN]]) procedure

Locks the file associated with PORT for reading or writing (according to whether PORT is an input- or output-port). START specifies the starting position in the file to be locked and defaults to 0. LEN specifies the length of the portion to be locked and defaults to #t, which means the complete file. file-lock returns a lock-object.

file-lock/blocking

(file-lock/blocking PORT [START [LEN]]) procedure

Similar to file-lock, but if a lock is held on the file, the current process blocks (including all threads) until the lock is released.

file-test-lock

(file-test-lock PORT [START [LEN]]) procedure

Tests whether the file associated with PORT is locked for reading or writing (according to whether PORT is an input- or output-port) and returns either #f or the process-id of the locking process.

file-unlock

(file-unlock LOCK) procedure

Unlocks the previously locked portion of a file given in LOCK.

Signal handling

set-alarm!

(set-alarm! SECONDS) procedure

Sets an internal timer to raise the signal/alrm after SECONDS are elapsed. You can use the set-signal-handler! procedure to write a handler for this signal.

set-signal-handler!

signal-handler

(signal-handler SIGNUM) procedure

Returns the signal handler for the code SIGNUM or #f.

(set-signal-handler! SIGNUM PROC) procedure

Establishes the procedure of one argument PROC as the handler for the signal with the code SIGNUM. PROC is called with the signal number as its sole argument. If the argument PROC is #f then any signal handler will be removed, and the corresponding signal set to SIG_IGN.

Notes

  • it is unspecified in which thread of execution the signal handler will be invoked.
  • when signals arrive in quick succession (specifically, before the handler for a signal has been started), then signals will be queued (up to a certain limit); the order in which the queued signals will be handled is not specified
  • (set! (signal-handler SIG) PROC) can be used as an alternative to (set-signal-handler! SIG PROC)
  • Any signal handlers for the signals signal/segv, signal/bus, signal/fpe and signal/ill will be ignored and these signals will always trigger an exception, unless the executable was started with the -:S runtime option. This feature is only available on platforms that support the sigprocmask(3) POSIX API function.

set-signal-mask!

(set-signal-mask! SIGLIST) procedure

Sets the signal mask of the current process to block all signals given in the list SIGLIST. Signals masked in that way will not be delivered to the current process.

signal-mask

(signal-mask) procedure

Returns the signal mask of the current process.

signal-masked?

(signal-masked? SIGNUM) procedure

Returns whether the signal for the code SIGNUM is currently masked.

signal-mask!

(signal-mask! SIGNUM) procedure

Masks (blocks) the signal for the code SIGNUM.

signal-unmask!

(signal-unmask! SIGNUM) procedure

Unmasks (unblocks) the signal for the code SIGNUM.

Signal codes

signal/term constant
signal/kill constant
signal/int constant
signal/hup constant
signal/fpe constant
signal/ill constant
signal/segv constant
signal/abrt constant
signal/trap constant
signal/quit constant
signal/alrm constant
signal/vtalrm constant
signal/prof constant
signal/io constant
signal/urg constant
signal/chld constant
signal/cont constant
signal/stop constant
signal/tstp constant
signal/pipe constant
signal/xcpu constant
signal/xfsz constant
signal/usr1 constant
signal/usr2 constant
signal/bus constant
signal/winch constant
signal/break constant

These variables contain signal codes for use with process-signal, set-signal-handler!, signal-handler, signal-masked?, signal-mask!, or signal-unmask!.

Environment access

get-environment-variables

(get-environment-variables) procedure

Returns a association list of the environment variables and their current values (see also SRFI-98).

setenv

(setenv VARIABLE VALUE) procedure

Sets the environment variable named VARIABLE to VALUE. Both arguments should be strings. If the variable is not defined in the environment, a new definition is created.

unsetenv

(unsetenv VARIABLE) procedure

Removes the definition of the environment variable VARIABLE from the environment of the current process. If the variable is not defined, nothing happens.

Memory mapped I/O

Memory mapped I/O takes the contents of a file descriptor and places them in memory.

memory-mapped-file?

(memory-mapped-file? X) procedure

Returns #t, if X is an object representing a memory mapped file, or #f otherwise.

map-file-to-memory

(map-file-to-memory ADDRESS LEN PROTECTION FLAG FILENO [OFFSET]) procedure

Maps a section of a file to memory using the C function mmap(). ADDRESS should be a foreign pointer object or #f; LEN specifies the size of the section to be mapped; PROTECTION should be one or more of the flags prot/read, prot/write, prot/exec or prot/none bitwise-iored together; FLAG should be one or more of the flags map/fixed, map/shared, map/private, map/anonymous or map/file; FILENO should be the file-descriptor of the mapped file. The optional argument OFFSET gives the offset of the section of the file to be mapped and defaults to 0. This procedure returns an object representing the mapped file section. The procedure move-memory! can be used to access the mapped memory.

memory-mapped-file-pointer

(memory-mapped-file-pointer MMAP) procedure

Returns a machine pointer to the start of the memory region to which the file is mapped.

unmap-file-from-memory

(unmap-file-from-memory MMAP [LEN]) procedure

Unmaps the section of a file mapped to memory using the C function munmap(). MMAP should be a mapped file as returned by the procedure map-file-to-memory. The optional argument LEN specifies the length of the section to be unmapped and defaults to the complete length given when the file was mapped.

Memory Mapped I/O Example

;; example-mmap.scm
;;
;; basic example of memory mapped I/O
;;
;; This example does no error checking or cleanup, and serves
;; only to demonstrate how the mmap functions work together.
;;
(use posix)
(use lolevel)

       ; open a file using the posix module, so we have the file descriptor.
(let* ((fd   (file-open "example-mmap.scm" (+ open/rdonly open/nonblock)))
       ; fstat(2) the file descriptor fd to determine its size
       (size (file-size fd))
       ; mmap(2) the file for reading.
       (mmap (map-file-to-memory #f
                                 size
                                 prot/read
                                 (+ map/file map/shared)
                                 fd))
       ; return a pointer object to the beginning of the memory map.
       (buf  (memory-mapped-file-pointer mmap))
       ; allocate a string the same size as the file.
       (str  (make-string size)))
  ; copy the mapped memory into a string
  (move-memory! buf str size)
  (display str)
  ; alternately, print the string byte-by-byte without copying.
  (let loop ((p buf)
             (i 0))
    (unless (= i size)
      (display (integer->char (pointer-s8-ref p)))
      (loop (pointer+ p 1) (+ i 1)))))

Date and time routines

seconds->local-time

(seconds->local-time [SECONDS]) procedure

Breaks down the time value represented in SECONDS into a 10 element vector of the form #(seconds minutes hours mday month year wday yday dstflag timezone), in the following format:

seconds (0)
the number of seconds after the minute (0 - 59)
minutes (1)
the number of minutes after the hour (0 - 59)
hours (2)
the number of hours past midnight (0 - 23)
mday (3)
the day of the month (1 - 31)
month (4)
the number of months since january (0 - 11)
year (5)
the number of years since 1900
wday (6)
the number of days since Sunday (0 - 6)
yday (7)
the number of days since January 1 (0 - 365)
dstflag (8)
a flag that is true if Daylight Saving Time is in effect at the time described.
timezone (9)
the difference between UTC and the latest local standard time, in seconds west of UTC.

SECONDS defaults to the value of (current-seconds).

local-time->seconds

(local-time->seconds VECTOR) procedure

Converts the ten-element vector VECTOR representing the time value relative to the current timezone into the number of seconds since the first of January, 1970 UTC.

local-timezone-abbreviation

(local-timezone-abbreviation) procedure

Returns the abbreviation for the local timezone as a string.

seconds->string

(seconds->string [SECONDS]) procedure

Converts the time represented in SECONDS into a local-time string of the form "Tue May 21 13:46:22 1991". SECONDS defaults to the value of (current-seconds).

seconds->utc-time

(seconds->utc-time [SECONDS]) procedure

Similar to seconds->local-time, but interpretes SECONDS as UTC time. SECONDS defaults to the value of (current-seconds).

utc-time->seconds

(utc-time->seconds VECTOR) procedure

Converts the ten-element vector VECTOR representing the UTC time value into the number of seconds since the first of January, 1970 UTC.

time->string

(time->string VECTOR [FORMAT]) procedure

Converts the broken down time represented in the 10 element vector VECTOR into a string of the form represented by the FORMAT string. The default time form produces something like "Tue May 21 13:46:22 1991".

The FORMAT string follows the rules for the C library procedure strftime. The default FORMAT string is "%a %b %e %H:%M:%S %Z %Y".

string->time

(string->time TIME [FORMAT]) procedure

Converts a string of the form represented by the FORMAT string into the broken down time represented in a 10 element vector. The default time form understands something like "Tue May 21 13:46:22 1991".

The FORMAT string follows the rules for the C library procedure strptime. The default FORMAT string is "%a %b %e %H:%M:%S %Z %Y".

Raw exit

_exit

(_exit [CODE]) procedure

Exits the current process without flushing any buffered output (using the C function _exit). Note that the exit-handler is not called when this procedure is invoked. The optional return-code CODE defaults to 0.

ERRNO values

errno/perm constant
errno/noent constant
errno/srch constant
errno/intr constant
errno/io constant
errno/noexec constant
errno/badf constant
errno/child constant
errno/nomem constant
errno/acces constant
errno/fault constant
errno/busy constant
errno/notdir constant
errno/isdir constant
errno/inval constant
errno/mfile constant
errno/nospc constant
errno/spipe constant
errno/pipe constant
errno/again constant
errno/rofs constant
errno/exist constant
errno/wouldblock constant

These variables contain error codes as returned by errno.

Finding files

find-files

(find-files DIRECTORY #!key test action seed limit dotfiles follow-symlinks) procedure

Recursively traverses the contents of DIRECTORY (which should be a string) and invokes the procedure action for all files in which the procedure test is true. test may be a procedure of one argument or an irregex object, regex string or SRE expression that will be matched with a full pathname using irregex-match. action should be a procedure of two arguments: the currently encountered file and the result of the previous invocation of action, or, if this is the first invocation, the value of seed. test defaults to (constantly #t), action defaults to cons, seed defaults to (). limit should be a procedure of one argument that is called for each nested directory and which should return true, if that directory is to be traversed recursively. limit may also be an exact integer that gives the maximum recursion depth. For example, a depth of 0 means that only files in the top-level, specified directory are to be traversed. In this case, all nested directories are ignored. limit may also be #f (the default), which is equivalent to (constantly #t).

If dotfiles is given and true, then files starting with a "." character will not be ignored (but note that "." and ".." are always ignored). if follow-symlinks is given and true, then the traversal of a symbolic link that points to a directory will recursively traverse the latter. By default, symbolic links are not followed.

Note that action is called with the full pathname of each file, including the directory prefix.

This procedure's signature was changed in CHICKEN 4.6. In older versions, find-files has a different signature:

 (find-files DIRECTORY [TEST [ACTION [SEED [LIMIT]]]])

The old signature was supported until CHICKEN 4.7.3 for compatibility reasons, at which point it became invalid. The optional arguments are ignored and use their default values, and no warning is issued. One symptom is that your TEST does not work, returning every file.

Getting the hostname and system information

get-host-name

(get-host-name) procedure

Returns the hostname of the machine that this process is running on.

system-information

(system-information) procedure

Invokes the UNIX system call uname() and returns a list of 5 values: system-name, node-name, OS release, OS version and machine.

Setting the file buffering mode

set-buffering-mode!

(set-buffering-mode! PORT MODE [BUFSIZE]) procedure

Sets the buffering-mode for the file associated with PORT to MODE, which should be one of the keywords #:full, #:line or #:none. If BUFSIZE is specified it determines the size of the buffer to be used (if any).

Terminal ports

terminal-name

(terminal-name PORT) procedure

Returns the name of the terminal that is connected to PORT.

terminal-port?

(terminal-port? PORT) procedure

Returns #t if PORT is connected to a terminal and #f otherwise.

terminal-size

(terminal-size PORT) procedure

Returns two values, the number of columns and rows of the terminal that is connected to PORT or 0, 0 if the terminal size can not be obtained. On Windows, this procedure always returns 0, 0.

How Scheme procedures relate to UNIX C functions

change-directory
chdir
change-directory*
fchdir
change-file-mode
chmod
change-file-owner
chown
create-directory
mkdir
create-fifo
mkfifo
create-pipe
pipe
create-session
setsid
create-symbolic-link
link
current-directory
curdir
current-effective-group-id
getegid
current-effective-user-id
geteuid
current-group-id
getgid
current-parent-id
getppid
current-process-id
getpid
current-user-id
getuid
delete-directory
rmdir
duplicate-fileno
dup/dup2
_exit
_exit
file-close
close
file-access-time
stat
file-change-time
stat
file-creation-mode
umask
file-modification-time
stat
file-execute-access?
access
file-open
open
file-lock
fcntl
file-position
ftell/lseek
file-read
read
file-read-access?
access
file-select
select
file-control
fcntl
file-stat
stat
file-test-lock
fcntl
file-truncate
truncate/ftruncate
file-unlock
fcntl
file-write
write
file-write-access?
access
get-groups
getgroups
get-host-name
gethostname
initialize-groups
initgroups
local-time->seconds
mktime
local-timezone-abbreviation
localtime
map-file-to-memory
mmap
open-input-file*
fdopen
open-output-file*
fdopen
open-input-pipe
popen
open-output-pipe
popen
port->fileno
fileno
process-execute
execvp
process-fork
fork
process-group-id
getpgid
process-signal
kill
process-wait
waitpid
close-input-pipe
pclose
close-output-pipe
pclose
read-symbolic-link
readlink
seconds->local-time
localtime
seconds->string
ctime
seconds->utc-time
gmtime
set-alarm!
alarm
set-buffering-mode!
setvbuf
set-file-position!
fseek/seek
set-groups!
setgroups
set-signal-mask!
sigprocmask
set-group-id!
setgid
set-process-group-id!
setpgid
set-user-id!
setuid
set-root-directory!
chroot
setenv
setenv/putenv
sleep
sleep
system-information
uname
terminal-name
ttyname
terminal-port?
isatty
time->string
asctime
unsetenv
putenv
unmap-file-from-memory
munmap
user-information
getpwnam/getpwuid
utc-time->seconds
timegm

Windows specific notes

Use of UTF8 encoded strings is for pathnames is not supported. Windows uses a 16-bit UNICODE encoding with special system calls for wide-character support. Only single-byte string encoding can be used.

Procedure Changes

Exceptions to the above procedure definitions.

(create-pipe [MODE]) procedure

The optional parameter MODE, default open/binary | open/noinherit. This can be open/binary or open/text, optionally or'ed with open/noinherit.

(process-wait [PID [NOHANG]]) procedure

process-wait always returns #t for a terminated process and only the exit status is available. (Windows does not provide signals as an interprocess communication method.)

(process-execute PATHNAME [ARGUMENT-LIST [ENVIRONMENT-LIST [EXACT-FLAG]]]) procedure
(process COMMAND ARGUMENT-LIST [ENVIRONMENT-LIST [EXACT-FLAG]]) procedure
(process* COMMAND ARGUMENT-LIST [ENVIRONMENT-LIST [EXACT-FLAG]]) procedure

The optional parameter EXACT-FLAG, default #f. When #f any argument string with embedded whitespace will be wrapped in quotes. When #t no such wrapping occurs.

Unsupported Definitions

The following definitions are not supported for native Windows builds (compiled with the Microsoft tools or with MinGW):

open/noctty  open/nonblock  open/fsync  open/sync
perm/isvtx  perm/isuid  perm/isgid
file-select file-control
signal/... (except signal/term, signal/int, signal/fpe, signal/ill, signal/segv, signal/abrt, signal/break)
set-signal-mask!  signal-mask  signal-masked?  signal-mask!  signal-unmask!
user-information  group-information  get-groups  set-groups!  initialize-groups
errno/wouldblock
change-directory*
change-file-owner
current-user-id  current-group-id  current-effective-user-id  current-effective-group-id
set-user-id!  set-group-id!
create-session
process-group-id  set-process-group-id!
create-symbolic-link  read-symbolic-link
file-truncate
file-lock  file-lock/blocking  file-unlock  file-test-lock
create-fifo  fifo?
set-alarm!
terminal-port?  terminal-name
process-fork  process-signal
parent-process-id
set-root-directory!
utc-time->seconds

Additional Definitions

Only available for Windows

This variable is a mode value for create-pipe. Useful when spawning a child process.

These variables contains special flags that specify the exact semantics of process-spawn: spawn/overlay replaces the current process with the new one. spawn/wait suspends execution of the current process until the spawned process returns. spawn/nowait does the opposite (spawn/nowaito is identical, according to the Microsoft documentation) and runs the process asynchronously. spawn/detach runs the new process in the background, without being attached to a console.

process-spawn

(process-spawn MODE COMMAND [ARGUMENT-LIST [ENVIRONMENT-LIST [EXACT-FLAG]]]) procedure

Creates and runs a new process with the given COMMAND filename and the optional ARGUMENT-LIST and ENVIRONMENT-LIST. MODE specifies how exactly the process should be executed and must be one or more of the spawn/... flags defined above.

The EXACT-FLAG, default #f, controls quote-wrapping of argument strings. When #t quote-wrapping is not performed.

Returns:

  • the exit status when synchronous
  • the PID when asynchronous
  • -1 when failure

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