#
Chapter 9
Access to POSIX

This chapter describes Scheme 48’s interface to the POSIX C calls [1]. Scheme versions of most of the functions in POSIX are provided. Both the interface and implementation are new and are likely to change in future releases. Section 9.10 lists which Scheme functions call which C functions.

Scheme 48’s POSIX interface will likely change significantly in the future. The implementation is new and may have significant bugs.

The POSIX bindings are available in several structures:

`posix-processes` | fork, exec, and friends
`posix-process-data` | information about processes
`posix-files` | files and directories
`posix-i/o` | operations on ports
`posix-time` | time functions
`posix-users` | users and groups
`posix-regexps` | regular expression matching
`posix` | all of the above

Scheme 48’s POSIX interface differs from Scsh’s [11, 12] in several ways. The interface here lacks Scsh’s high-level constructs and utilities, such as the process notation, `awk` procedure, and parsing utilities. Scheme 48 uses distinct types for some values that Scsh leaves as symbols or unboxed integers; these include file types, file modes, and user and group ids. Many of the names and other interface details are different, as well.

## 9.1 Process primitives

The procedures described in this section control the creation of processes and the execution of programs. They are in the structures `posix-process` and `posix`.

### 9.1.1 Process creation and termination

- `(fork) –> process-id or `#f``

- `(fork-and-forget thunk)`

`Fork` creates a new child process and returns the child’s process-id in the parent and `#f` in the child. `Fork-and-forget` calls thunk in a new process; no process-id is returned. `Fork-and-forget` uses an intermediate process to avoid creating a zombie process.

- `(process-id? x) –> boolean`

- `(process-id=? process-id0 process-id1) –> boolean`

- `(process-id->integer process-id) –> integer`

- `(integer->process-id integer) –> process-id`

`Process-id?` is a predicate for process-ids, `process-id=?` compares two to see if they are the same, and `process-id-uid` returns the actual Unix id. `Process-id->integer` and `integer->process-id` convert process ids to and from integers.

- `(process-id-exit-status process-id) –> integer or `#f``

- `(process-id-terminating-signal process-id) –> signal or `#f``

- `(wait-for-child-process process-id)`

If a process terminates normally `process-id-exit-status` will return its exit status. If the process is still running or was terminated by a signal then `process-id-exit-status` will return `#f`. Similarly, if a child process was terminated by a signal `process-id-terminating-signal` will return that signal and will return `#f` if the process is still running or terminated normally. `Wait-for-child-process` blocks until the child process terminates. Scheme 48 may reap child processes before the user requests their exit status, but it does not always do so.

- `(exit status)`

Terminates the current process with the integer status as its exit status.

### 9.1.2 `Exec`

- `(exec program-name arg0 `...`)`

- `(exec-with-environment program-name env arg0 `...`)`

- `(exec-file filename arg0 `...`)`

- `(exec-file-with-environment filename env arg0 `...`)`

- `(exec-with-alias name lookup? maybe-env arguments)`

All of these replace the current program with a new one. They differ in how the new program is found, what its environment is, and what arguments it is passed. `Exec` and `exec-with-environment` look up the new program in the search path, while `exec-file` and `exec-file-with-environment` execute a particular file. The environment is either inherited from the current process (`exec` and `exec-file`) or given as an argument (``...`-with-environment`). Program-name and filename and any argi should be os-string-thing arguments (see section 5.15. Env should be a list of os-string-thing arguments of the form `"name=value"`. The first four procedures add their first argument, program-name or filename, before the arg0 `...` arguments.

`Exec-with-alias` is an omnibus procedure that subsumes the other four. Name is looked up in the search path if lookup? is true and is used as a filename otherwise. Maybe-env is either a list of os-string-things for the environment of the new program or `#f` in which case the new program inherits its environment from the current one. Arguments should be a list of os-string-things; unlike with the other four procedures, name is not added to this list (hence `-with-alias`).

## 9.2 Signals

There are two varieties of signals available, named and anonymous. A named signal is one for which we have a symbolic name, such as `kill` or `pipe`. Anonymous signals, for which we only have the current operating system’s signal number, have no meaning in other operating systems. Named signals preserve their meaning in image files. Not all named signals are available from all OS’s and there may be multiple names for a single OS signal number.

- `(signal signal-name) –> signal` (syntax)

- `(name->signal symbol) –> signal or `#f``

- `(integer->signal integer) –> signal`

- `(signal? x) –> boolean`

- `(signal-name signal) –> symbol or `#f``

- `(signal-os-number signal) –> integer`

- `(signal=? signal0 signal1) –> boolean`

The syntax `signal` returns a (named) signal associated with signal-name. `Name->signal` returns a (named) signal or `#f` if the the signal name is not supported by the operating system. The signal returned by `integer->signal` is a named signal if integer corresponds to a named signal in the current operating system; otherwise it returns an anonymous signal. `Signal-name` returns a symbol if signal is named and `#f` if it is anonymous. `Signal=?` returns `#t` if signal0 and signal1 have the same operating system number and `#f` if they do not.

### 9.2.1 POSIX signals

The following lists the names of the POSIX signals.

`abrt` | abort - abnormal termination (as by abort())
`alrm` | alarm - timeout signal (as by alarm())
`fpe` | floating point exception
`hup` | hangup - hangup on controlling terminal or death of controlling process
`ill` | illegal instruction
`int` | interrupt - interaction attention
`kill` | kill - termination signal, cannot be caught or ignored
`pipe` | pipe - write on a pipe with no readers
`quit` | quit - interaction termination
`segv` | segmentation violation - invalid memory reference
`term` | termination - termination signal
`usr1` | user1 - for use by applications
`usr2` | user2 - for use by applications
`chld` | child - child process stopped or terminated
`cont` | continue - continue if stopped
`stop` | stop - cannot be caught or ignored
`tstp` | interactive stop
`ttin` | read from control terminal attempted by background process
`ttou` | write to control terminal attempted by background process
`bus` | bus error - access to undefined portion of memory

### 9.2.2 Other signals

The following lists the names of the non-POSIX signals that the system is currently aware of.

`trap` | trace or breakpoint trap
`iot` | IOT trap - a synonym for ABRT
`emt` |
`sys` | bad argument to routine (SVID)
`stkflt` | stack fault on coprocessor
`urg` | urgent condition on socket (4.2 BSD)
`io` | I/O now possible (4.2 BSD)
`poll` | A synonym for SIGIO (System V)
`cld` | A synonym for SIGCHLD
`xcpu` | CPU time limit exceeded (4.2 BSD)
`xfsz` | File size limit exceeded (4.2 BSD)
`vtalrm` | Virtual alarm clock (4.2 BSD)
`prof` | Profile alarm clock
`pwr` | Power failure (System V)
`info` | A synonym for SIGPWR
`lost` | File lock lost
`winch` | Window resize signal (4.3 BSD, Sun)
`unused` | Unused signal

### 9.2.3 Sending signals

- `(signal-process process-id signal)`

Send signal to the process corresponding to process-id.

### 9.2.4 Receiving signals

Signals received by the Scheme process can be obtained via one or more signal-queues. Each signal queue has a list of monitored signals and a queue of received signals that have yet to be read from the signal-queue. When the Scheme process receives a signal that signal is added to the received-signal queues of all signal-queues which are currently monitoring that particular signal.

- `(make-signal-queue signals) –> signal-queue`

- `(signal-queue? x) –> boolean`

- `(signal-queue-monitored-signals signal-queue) –> list of signals`

- `(dequeue-signal! signal-queue) –> signal`

- `(maybe-dequeue-signal! signal-queue) –> signal or `#f``

`Make-signal-queue` returns a new signal-queue that will monitor the signals in the list signals. `Signal-queue?` is a predicate for signal queues. `Signal-queue-monitored-signals` returns a list of the signals currently monitored by signal-queue. `Dequeue-signal!` and `maybe-dequeue-signal` both return the next received-but-unread signal from signal-queue. If signal-queue’s queue of signals is empty `dequeue-signal!` blocks until an appropriate signal is received. `Maybe-dequeue-signal!` does not block; it returns `#f` instead.

There is a bug in the current system that causes an erroneous deadlock error if threads are blocked waiting for signals and no other threads are available to run. A work around is to create a thread that sleeps for a long time, which prevents any deadlock errors (including real ones):

    > ,open threads
    > (spawn (lambda ()
               ; Sleep for a year
               (sleep (* 1000 60 60 24 365))))

- `(add-signal-queue-signal! signal-queue signal)`

- `(remove-signal-queue-signal! signal-queue signal)`

These two procedures can be used to add or remove signals from a signal-queue’s list of monitored signals. When a signal is removed from a signal-queue’s list of monitored signals any occurances of the signal are removed from that signal-queue’s pending signals. In other words, `dequeue-signal!` and `maybe-dequeue-signal!` will only return signals that are currently on the signal-queue’s list of signals.

## 9.3 Process environment

These are in structures `posix-process-data` and `posix`.

### 9.3.1 Process identification

- `(get-process-id) –> process-id`

- `(get-parent-process-id) –> process-id`

These return the process ids of the current process and its parent. See section 9.1.1 for operations on process ids.

- `(get-user-id) –> user-id`

- `(get-effective-user-id) –> user-id`

- `(set-user-id! user-id)`

- `(get-group-id) –> group-id`

- `(get-effective-group-id) –> group-id`

- `(set-group-id! group-id)`

Every process has both the original and effective user id and group id. The effective values may be set, but not the original ones.

- `(get-groups) –> group-ids`

- `(get-login-name) –> os-string`

`Get-groups` returns a list of the supplementary groups of the current process. `Get-login-name` returns a user name for the current process.

### 9.3.2 Environment variables

- `(lookup-environment-variable os-string-thing) –> os-string or `#f``

- `(environment-alist) –> alist`

`Lookup-environment-variable` looks up its argument in the environment list and returns the corresponding value or `#f` if there is none. `Environment-alist` returns the entire environment as a list of `(name-os-string . value-os-string)` pairs.

## 9.4 Users and groups

User-ids and group-ids are boxed integers representing Unix users and groups. The procedures in this section are in structures `posix-users` and `posix`.

- `(user-id? x) –> boolean`

- `(user-id=? user-id0 user-id1) –> boolean`

- `(user-id->integer user-id) –> integer`

- `(integer->user-id integer) –> user-id`

- `(group-id? x) –> boolean`

- `(group-id=? group-id0 group-id1) –> boolean`

- `(group-id->integer group-id) –> integer`

- `(integer->group-id integer) –> group-id`

User-ids and group-ids have their own own predicates and comparison, boxing, and unboxing functions.

- `(user-id->user-info user-id) –> user-info`

- `(name->user-info os-string) –> user-info`

These return the user info for a user identified by user-id or name.

- `(user-info? x) –> boolean`

- `(user-info-name user-info) –> os-string`

- `(user-info-id user-info) –> user-id`

- `(user-info-group user-info) –> group-id`

- `(user-info-home-directory user-info) –> os-string`

- `(user-info-shell user-info) –> os-string`

A `user-info` contains information about a user. Available are the user’s name, id, group, home directory, and shell.

- `(group-id->group-info group-id) –> group-info`

- `(name->group-info os-string) –> group-info`

These return the group info for a group identified by group-id or name.

- `(group-info? x) –> boolean`

- `(group-info-name group-info) –> os-string`

- `(group-info-id group-info) –> group-id`

- `(group-info-members group-info) –> user-ids`

A `group-info` contains information about a group. Available are the group’s name, id, and a list of members.

## 9.5 OS and machine identification

These procedures return strings that are supposed to identify the current OS and machine. The POSIX standard does not indicate the format of the strings. The procedures are in structures `posix-platform-names` and `posix`.

- `(os-name) –> string`

- `(os-node-name) –> string`

- `(os-release-name) –> string`

- `(os-version-name) –> string`

- `(machine-name) –> string`

## 9.6 Files and directories

These procedures are in structures `posix-files` and `posix`.

### 9.6.1 Directory streams

Directory streams are like input ports, with each read operation returning the next name in the directory.

- `(open-directory-stream name) –> directory`

- `(directory-stream? x) –> boolean`

- `(read-directory-stream directory) –> name or `#f``

- `(close-directory-stream directory)`

`Open-directory-stream` opens a new directory stream. `Directory-stream?` is a predicate that recognizes directory streams. `Read-directory-stream` returns the next name in the directory or `#f` if all names have been read. `Close-directory-stream` closes a directory stream.

- `(list-directory name) –> list of os-strings`

This is the obvious utility; it returns a list of the names in directory name.

### 9.6.2 Working directory

- `(working-directory) –> os-string`

- `(set-working-directory! os-string-thing)`

These return and set the working directory.

### 9.6.3 File creation and removal

- `(open-file path file-options) –> port`

- `(open-file path file-options file-mode) –> port`

`Open-file` opens a port to the file named by path, which must be a os-string-thing argument. The file-options argument determines various aspects of the returned port. The optional file-mode argument is used only if the file to be opened does not already exist. The returned port is an input port if file-options includes `read-only`; otherwise it returns an output port. `Dup-switching-mode` can be used to open an input port for output ports opened with the `read/write` option.

- `(file-options file-option-name `...`) –> file-options` (syntax)

- `(file-options-on? file-options file-options) –> boolean`

- `(file-options-union file-options file-options) –> file-options`

The syntax `file-options` returns a file-option with the indicated options set. `File-options-on?` returns true if its first argument includes all of the options listed in the second argument. `File-options-union` returns a file-options argument containing exactly all of the options listed in either argument. The following file options may be used with `open-file`.

| `create` | create file if it does not already exist; a file-mode argument is required with this option
| `exclusive` | an error will be raised if this option and `create` are both set and the file already exists
| `no-controlling-tty` | if path is a terminal device this option causes the terminal to not become the controlling terminal of the process
| `truncate` | file is truncated
| `append` | writes are appended to existing contents
| `nonblocking` | read and write operations do not block
| `read-only` | port may not be written
| `read-write` | file descriptor may be read or written
| `write-only` | port may not be read

Only one of the last three options may be used. If `read-write` is specified, an output port is returned.

For example

    (open-file "some-file.txt"
               (file-options create write-only)
               (file-mode read owner-write))

returns an output port that writes to a newly-created file that can be read by anyone and written only by the owner. Once the file exists,

    (open-file "some-file.txt"
               (file-options append write-only))

will open an output port that appends to the file.

The `append` and `nonblocking` options and the read/write nature of the port can be read using `i/o-flags`. The `append` and `nonblocking` options can be set using `set-i/o-flags!`.

To keep port operations from blocking the Scheme 48 process, output ports are set to be nonblocking at the time of creation (input ports are managed using `select()`). You can use `set-i/o-flags!` to make an output port blocking, for example just before a fork, but care should be exercised. The Scheme 48 runtime code may get confused if an I/O operation blocks.

- `(set-file-creation-mask! file-mode)`

Sets the file creation mask to be file-mode. Bits set in file-mode are cleared in the modes of any files or directories created by the current process.

- `(link existing new)`

Both existing and new must be os-string-thing arguments. `Link` makes path new be a new link to the file pointed to by path existing. The two paths must be in the same file system.

- `(make-directory path file-mode)`

- `(make-fifo path file-mode)`

These two procedures make new directories and fifo files. In both cases, path must be a os-string-thing argument.

- `(unlink path)`

- `(remove-directory path)`

- `(rename old-path new-path)`

Path, old-path and new-path must all be os-string-thing arguments. `Unlink` removes the link indicated by path. `Remove-directory` removes the indicated (empty) directory. `Rename` moves the file pointed to by old-path to the location pointed to by new-path (the two paths must be in the same file system). Any other links to the file remain unchanged.

- `(accessible? path access-mode . more-modes) –> boolean`

- `(access-mode mode-name) –> access-mode` (syntax)

`Accessible?` returns true if path (which must be a os-string-thing argument) is a file that can be accessed in the listed mode. If more than one mode is specified `accessible?` returns true if all of the specified modes are permitted. The mode-names are: `read`, `write`, `execute`, `exists`.

### 9.6.4 File information

- `(get-file-info path) –> file-info`

- `(get-file/link-info name) –> file-info`

- `(get-port-info fd-port) –> file-info`

`Get-file-info` and `get-file/link-info` both return a file info record for the file named by path, which must be a os-string-thing argument. `Get-file-info` follows symbolic links while `get-file/link-info` does not. `Get-port-info` returns a file info record for the file which port reads from or writes to. An error is raised if fd-port does not read from or write to a file descriptor.

- `(file-info? x) –> boolean`

- `(file-info-name file-info) –> os-string`

`File-info?` is a predicate for file-info records. `File-info-name` is the name which was used to get `file-info`, either as passed to `get-file-info` or `get-file/link-info`, or used to open the port passed to `get-port-info`.

- `(file-info-type file-info) –> file-type`

- `(file-type? x) –> boolean`

- `(file-type-name file-type) –> symbol`

- `(file-type type) –> file-type` (syntax)

`File-info-type` returns the type of the file, as a file-type object File types may be compared using `eq?`. The valid file types are:

`regular`
`directory`
`character-device`
`block-device`
`fifo`
`symbolic-link`
`socket`
`other`

`Symbolic-link` and `socket` are not required by POSIX.

- `(file-info-device file-info) –> integer`

- `(file-info-inode file-info) –> integer`

The device and inode numbers uniquely determine a file.

- `(file-info-link-count file-info) –> integer`

- `(file-info-size file-info) –> integer`

These return the number of links to a file and the file size in bytes. The size is only meaningful for regular files.

- `(file-info-owner file-info) –> user-id`

- `(file-info-group file-info) –> group-id`

- `(file-info-mode file-info) –> file-mode`

These return the owner, group, and access mode of a file.

- `(file-info-last-access file-info) –> time`

- `(file-info-last-modification file-info) –> time`

- `(file-info-last-info-change file-info) –> time`

These return the time the file was last read, modified, or had its status modified

### 9.6.5 File modes

A file mode is a boxed integer representing a file protection mask.

- `(file-mode permission-name `...`) –> file-mode` (syntax)

- `(file-mode? x) –> boolean`

- `(file-mode+ file-mode `...`) –> file-mode`

- `(file-mode- file-mode0 file-mode1) –> file-mode`

`File-mode` is syntax for creating file modes. The mode-names are listed below. `File-mode?` is a predicate for file modes. `File-mode+` returns a mode that contains all of permissions of its arguments. `File-mode-` returns a mode that has all of the permissions of file-mode0 that are not in file-mode1.

- `(file-mode=? file-mode0 file-mode1) –> boolean`

- `(file-mode<=? file-mode0 file-mode1) –> boolean`

- `(file-mode>=? file-mode0 file-mode1) –> boolean`

`File-mode=?` returns true if the two modes are exactly the same. `File-mode<=?` returns true if file-mode0 has a subset of the permissions of file-mode1. `File-mode>=?` is `file-mode<=?` with the arguments reversed.

- `(file-mode->integer file-mode) –> integer`

- `(integer->file-mode integer) –> file-mode`

`Integer->file-mode` and `file-mode->integer` translate file modes to and from the classic Unix file mode masks. These may not be the masks used by the underlying OS.

Permission name | Bit mask
`set-uid` | `#o4000` | set user id when executing
`set-gid` | `#o2000` | set group id when executing
`owner-read` | `#o0400` | read by owner
`owner-write` | `#o0200` | write by owner
`owner-exec` | `#o0100` | execute (or search) by owner
`group-read` | `#o0040` | read by group
`group-write` | `#o0020` | write by group
`group-exec` | `#o0010` | execute (or search) by group
`other-read` | `#o0004` | read by others
`other-write` | `#o0002` | write by others
`other-exec` | `#o0001` | execute (or search) by others

Names for sets of permissions
`owner` | `#o0700` | read, write, and execute by owner
`group` | `#o0070` | read, write, and execute by group
`other` | `#o0007` | read, write, and execute by others
`read` | `#o0444` | read by anyone
`write` | `#o0222` | write by anyone
`exec` | `#o0111` | execute by anyone
`all` | `#o0777` | anything by anyone

## 9.7 Time

These procedures are in structures `posix-time` and `posix`.

- `(make-time integer) –> time`

- `(current-time) –> time`

- `(time? x) –> boolean`

- `(time-seconds time) –> integer`

A `time` record contains an integer that represents time as the number of second since the Unix epoch (00:00:00 GMT, January 1, 1970). `Make-time` and `current-time` return `time`s, with `make-time`’s using its argument while `current-time`’s has the current time. `Time?` is a predicate that recognizes `time`s and `time-seconds` returns the number of seconds time represents.

- `(time=? time time) –> boolean`

- `(time<? time time) –> boolean`

- `(time<=? time time) –> boolean`

- `(time>? time time) –> boolean`

- `(time>=? time time) –> boolean`

These perform various comparison operations on the `time`s.

- `(time->string time) –> string`

`Time->string` returns a string representation of time in the following form.

    "Wed Jun 30 21:49:08 1993
    "

## 9.8 I/O

These procedures are in structures `posix-i/o` and `posix`.

- `(open-pipe) –> input-port + output-port`

`Open-pipe` creates a new pipe and returns the two ends as an input port and an output port.

A file descriptor port (or fd-port) is a port that reads to or writes from an OS file descriptor. Fd-ports are returned by `open-input-file`, `open-output-file`, `open-file`, `open-pipe`, and other procedures.

- `(fd-port? port) –> boolean`

- `(port->fd port) –> integer or `#f``

`Fd-port?` returns true if its argument is an fd-port. `Port->fd` returns the file descriptor associated with or `#f` if port is not an fd-port.

- `(remap-file-descriptors fd-spec `...`)`

`Remap-file-descriptors` reassigns file descriptors to ports. The fd-specs indicate which port is to be mapped to each file descriptor: the first gets file descriptor `0`, the second gets `1`, and so forth. A fd-spec is either a port that reads from or writes to a file descriptor, or `#f`, with `#f` indicating that the corresponding file descriptor is not used. Any open ports not listed are marked ‘close-on-exec’. The same port may be moved to multiple new file descriptors.

For example,

    (remap-file-descriptors (current-output-port)
                            #f
                            (current-input-port))

moves the current output port to file descriptor `0` and the current input port to file descriptor `2`.

- `(dup fd-port) –> fd-port`

- `(dup-switching-mode fd-port) –> fd-port`

- `(dup2 fd-port file-descriptor) –> fd-port`

These change fd-port’s file descriptor and return a new port that uses ports’s old file descriptor. `Dup` uses the lowest unused file descriptor and `dup2` uses the one provided. `Dup-switching-mode` is the same as `dup` except that the returned port is an input port if the argument was an output port and vice versa. If any existing port uses the file descriptor passed to `dup2`, that port is closed.

- `(close-all-but port `...`)`

`Close-all-but` closes all file descriptors whose associated ports are not passed to it as arguments.

- `(close-on-exec? port) –> boolean`

- `(set-close-on-exec?! port boolean)`

`Close-on-exec?` returns true if `port` will be closed when a new program is exec’ed. `Set-close-on-exec?!` sets `port`’s close-on-exec flag.

- `(i/o-flags port) –> file-options`

- `(set-i/o-flags! port file-options)`

These two procedures read and write various options for `port`. The options that can be read are `append`, `nonblocking`, `read-only`, `write-only`, and `read/write`. Only the `append` and `nonblocking` can be written.

- `(port-is-a-terminal? port) –> boolean`

- `(port-terminal-name port) –> string`

`Port-is-a-terminal?` returns true if port has an underlying file descriptor that is associated with a terminal. For such ports `port-terminal-name` returns the name of the terminal, for all others it returns `#f`.

## 9.9 Regular expressions

The procedures in this section provide access to POSIX regular expression matching. The regular expression syntax and semantics are far too complex to be described here. Due to limitations in the underlying facility, only Latin-1 strings are guaranteed to work here—on some platforms, only ASCII may function correctly. Moreover, because the C interface uses zero bytes for marking the ends of strings, patterns and strings that contain zero bytes will not work correctly.

These procedures are in structures `posix-regexps` and `posix`.

An abstract data type for creating POSIX regular expressions is described in section 5.20.

- `(make-regexp string . regexp-options) –> regexp`

- `(regexp-option option-name) –> regexp-option` (syntax)

`Make-regexp` makes a new regular expression, using string as the pattern. The possible option names are:

`extended` | use the extended patterns
`ignore-case` | ignore case when matching
`submatches` | report submatches
`newline` | treat newlines specially

The regular expression is not compiled until it matched against a string, so any errors in the pattern string will not be reported until that point.

- `(regexp? x) –> boolean`

This is a predicate for regular expressions.

- `(regexp-match regexp string start submatches? starts-line? ends-line?)`

  `–> boolean or list of matches`

- `(match? x) –> boolean`

- `(match-start match) –> integer`

- `(match-end match) –> integer`

`Regexp-match` matches the regular expression against the characters in string, starting at position start. If the string does not match the regular expression, `regexp-match` returns `#f`. If the string does match, then a list of match records is returned if submatches? is true, or `#t` is returned if it is not. Each match record contains the index of the character at the beginning of the match and one more than the index of the character at the end. The first match record gives the location of the substring that matched regexp. If the pattern in regexp contained submatches, then the results of these are returned in order, with a match records reporting submatches that succeeded and `#f` in place of those that did not.

Starts-line? should be true if string starts at the beginning of a line and ends-line? should be true if it ends one.

## 9.10 C to Scheme correspondence

The following table lists the Scheme procedures that correspond to particular C procedures. Not all of the Scheme procedures listed are part of the POSIX interface.

C procedure | Scheme procedure(s)
C procedure | Scheme procedure(s)
`access` | `accessible?`
`chdir` | `set-working-directory!`
`close` | `close-input-port, close-output-port,`
| `close-channel, close-socket`
`closedir` | `close-directory-stream`
`creat` | `open-file`
`ctime` | `time->string`
`dup` | `dup, dup-switching-mode`
`dup2` | `dup2`
`exec[l|v][e|p|ε]` | `exec, exec-with-environment,`
| `exec-file, exec-file-with-environment,`
| `exec-with-alias`
`_exit` | `exit`
`fcntl` | `io-flags, set-io-flags!,`
| `close-on-exec, set-close-on-exec!`
`fork` | `fork, fork-and-forget`
`fstat` | `get-port-info`
`getcwd` | `working-directory`
`getegid` | `get-effective-group-id`
`getenv` | `lookup-environment-variable,`
| `environment-alist`
`geteuid` | `get-effective-user-id`
`getgid` | `get-group-id`
`getgroups` | `get-groups`
`getlogin` | `get-login-name`
`getpid` | `get-process-id`
`getppid` | `get-parent-process-id`
`getuid` | `get-user-id`
`isatty` | `port-is-a-terminal?`
`link` | `link`
`lstat` | `get-file/link-info`
`mkdir` | `make-directory`
`mkfifo` | `make-fifo`
`open` | `open-file`
`opendir` | `open-directory-stream`
`pipe` | `open-pipe`
`read` | `read-char, read-block`
`readdir` | `read-directory-stream`
`rename` | `rename`
`rmdir` | `remove-directory`
`setgid` | `set-group-id!`
`setuid` | `set-user-id!`
`stat` | `get-file-info`
`time` | `current-time`
`ttyname` | `port-terminal-name`
`umask` | `set-file-creation-mask!`
`uname` | `os-name, os-node-name,`
| `os-release-name, os-version-name,`
| `machine-name`
`unlink` | `unlink`
`waitpid` | `wait-for-child-process`
`write` | `write-char, write-block`