12.1.5 File Ports
A port created by open-input-file, open-output-file,
subprocess, and related functions is a file-stream
port. The initial input, output, and error ports in racket
are also file-stream ports. The file-stream-port? predicate
recognizes file-stream ports.
When an input or output file-stream port is created, it is placed into
the management of the current custodian (see
Custodians).
Opens the file specified by path for input. The
mode-flag argument specifies how the file’s bytes are
translated on input:
'binary – bytes are returned from the port
exactly as they are read from the file.
'text – return and linefeed bytes (10 and
13) as read from the file are filtered by the port in a platform
specific manner:
Unix and Mac OS X: no filtering occurs.
Windows: a return-linefeed combination from a file is returned
by the port as a single linefeed; no filtering occurs for
return bytes that are not followed by a linefeed, or for a
linefeed that is not preceded by a return.
Under Windows, 'text mode works only with regular files;
attempting to use 'text with other kinds of files triggers an
exn:fail:filesystem exception.
Otherwise, the file specified by path need not be a regular
file. It might a device that is connected through the filesystem, such
as "aux" under Windows or "/dev/null" under Unix. In all
cases, the port is buffered by default.
The port produced by open-input-file should be explicitly
closed, either though close-input-port or indirectly via
custodian-shutdown-all, to release the OS-level file
handle. The input port will not be closed automatically if it is
otherwise available for garbage collection (see
Garbage Collection); a will could be associated input port
to close it more automatically (see Wills and Executors).
A path value that is the cleansed version of
path is used as the name of the opened port.
|
| path : path-string? |
| mode-flag : (or/c 'binary 'text) = 'binary |
| | exists-flag | | : | | | (or/c 'error 'append 'update 'can-update | | 'replace 'truncate | | 'must-truncate 'truncate/replace) |
| | | | | = | | 'error |
|
Opens the file specified by path for output. The
mode-flag argument specifies how bytes written to the port
are translated when written to the file:
'binary – bytes are written to the file exactly
as written to the port.
'text – under Windows, a linefeed byte (10) written
to the port is translated to a return-linefeed combination in the
file; no filtering occurs for returns.
Under Windows, 'text mode works only with regular files;
attempting to use 'text with other kinds of files triggers an
exn:fail:filesystem exception.
The exists-flag argument specifies how to handle/require
files that already exist:
'error – raise exn:fail:filesystem
if the file exists.
'replace – remove the old file, if it
exists, and write a new one.
'truncate – remove all old data, if the file
exists.
'must-truncate – remove all old data in an
existing file; if the file does not exist, the
exn:fail:filesystem exception is raised.
'truncate/replace – try 'truncate;
if it fails (perhaps due to file permissions), try
'replace.
'update – open an existing file without
truncating it; if the file does not exist, the
exn:fail:filesystem exception is raised. Use file-position
to change the current read/write position.
'can-update – open an existing file without
truncating it, or create the file if it does not exist.
'append – append to the end of the file,
whether it already exists or not; under Windows,
'append is equivalent to 'update, except that
the file is not required to exist, and the file position is
immediately set to the end of the file after opening it.
The file specified by path need not be a regular file. It
might a device that is connected through the filesystem, such as
"aux" under Windows or "/dev/null" under Unix. The output
port is block-buffered by default, unless the file corresponds to a
terminal, in which case is it line buffered bu default.
The port produced by open-output-port should be explicitly
closed, either though close-output-port or indirectly via
custodian-shutdown-all, to release the OS-level file
handle. The output port will not be closed automatically if it is
otherwise available for garbage collection (see
Garbage Collection); a will could be associated input port
to close it more automatically (see Wills and Executors).
A path value that is the cleansed version of
path is used as the name of the opened port.
|
|
| path : path-string? |
| mode-flag : (or/c 'binary 'text) = 'binary |
| | exists-flag | | : | | | (or/c 'error 'append 'update | | 'replace 'truncate 'truncate/replace) |
| | | | | = | | 'error |
|
Like
open-output-file, but producing two values: an input
port and an output port. The two ports are connected in that they
share the underlying file device. This procedure is intended for use
with special devices that can be opened by only one process, such as
"COM1" in Windows. For regular files, sharing the device can be
confusing. For example, using one port does not automatically flush
the other port’s buffer, and reading or writing in one port moves the
file position (if any) for the other port. For regular files, use
separate
open-input-file and
open-output-file calls
to avoid confusion.
Calls
open-input-file with the
path and
mode-flag arguments, and passes the resulting port
to
proc. The result of
proc is the result of the
call-with-input-file call, but the newly opened port is closed
when
thunk return.
Examples: |
|
|
"text in a file" |
|
| path : path-string? |
| proc : (output-port? . -> . any) |
| mode-flag : (or/c 'binary 'text) = 'binary |
| | exists-flag | | : | | | (or/c 'error 'append 'update | | 'replace 'truncate 'truncate/replace) |
| | | | | = | | 'error |
|
Like
call-with-input-file, but the newly opened port is
closed whenever control escapes the dynamic extent of the
call-with-input-file* call, whether through
proc’s
return, a continuation application, or a prompt-based abort.
|
| path : path-string? |
| proc : (output-port? . -> . any) |
| mode-flag : (or/c 'binary 'text) = 'binary |
| | exists-flag | | : | | | (or/c 'error 'append 'update | | 'replace 'truncate 'truncate/replace) |
| | | | | = | | 'error |
|
Like
call-with-output-file, but the newly opened port is
closed whenever control escapes the dynamic extent of the
call-with-output-file* call, whether through
proc’s
return, a continuation application, or a prompt-based abort.
|
| path : path-string? |
| thunk : (-> any) |
| mode-flag : (or/c 'binary 'text) = 'binary |
| | exists-flag | | : | | | (or/c 'error 'append 'update | | 'replace 'truncate 'truncate/replace) |
| | | | | = | | 'error |
|
Returns a number that represents
the identity of the device and file read or written by
port. For two ports whose open times overlap, the
result of
port-file-identity is the same for both ports if
and only if the ports access the same device and file. For ports whose
open times do not overlap, no guarantee can be provided for the port
identities (even if the ports actually access the same file) – except
as can be inferred through relationships with other ports. If
port is closed, the
exn:fail exception is raised. Under
Windows 95, 98, and Me, if
port is connected to a
pipe instead of a file, the
exn:fail:filesystem exception is raised.