Tcl Built-In Commands fconfigure(1T)
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NAME
fconfigure - Set and get options on a channel
SYNOPSIS
fconfigure channelId
fconfigure channelId name
fconfigure channelId name value ?name value ...?
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DESCRIPTION
The fconfigure command sets and retrieves options for chan-
nels. ChannelId identifies the channel for which to set or query an option and must refer to an open channel such as a Tcl standard channel (stdin, stdout, or stderr), the return value from an invocation of open or socket, or the result of a channel creation command provided by a Tcl extension. If no name or value arguments are supplied, the command returns a list containing alternating option names and values for the channel. If name is supplied but no value then the command returns the current value of the givenoption. If one or more pairs of name and value are sup-
plied, the command sets each of the named options to the corresponding value; in this case the return value is an empty string. The options described below are supported for all channels. In addition, each channel type may add options that only it supports. See the manual entry for the command that creates each type of channels for the options that that specific type of channel supports. For example, see the manual entry for the socket command for its additional options.-blocking boolean
The -blocking option determines whether I/O operations
on the channel can cause the process to block indefin-
itely. The value of the option must be a proper boolean value. Channels are normally in blocking mode; if a channel is placed into nonblocking mode it will affect the operation of the gets, read, puts, flush, and close commands; see the documentation for those commands for details. For nonblocking mode to work correctly, the application must be using the Tcl eventloop (e.g. by calling Tcl_DoOneEvent or invoking the
vwait command).-buffering newValue
If newValue is full then the I/O system will buffer Tcl Last change: 8.3 1
Tcl Built-In Commands fconfigure(1T)
output until its internal buffer is full or until the flush command is invoked. If newValue is line, then theI/O system will automatically flush output for the channel whenever a newline character is output. If
newValue is none, the I/O system will flush automati-
cally after every output operation. The default is for-buffering to be set to full except for channels that
connect to terminal-like devices; for these channels
the initial setting is line. Additionally, stdin and stdout are initially set to line, and stderr is set to none.-buffersize newSize
Newvalue must be an integer; its value is used to set the size of buffers, in bytes, subsequently allocated for this channel to store input or output. Newvalue must be between ten and one million, allowing buffers of ten to one million bytes in size.-encoding name
This option is used to specify the encoding of the channel, so that the data can be converted to and from Unicode for use in Tcl. For instance, in order for Tcl to read characters from a Japanese file in shiftjis and properly process and display the contents, the encoding would be set to shiftjis. Thereafter, when reading from the channel, the bytes in the Japanese file would be converted to Unicode as they are read. Writing isalso supported - as Tcl strings are written to the
channel they will automatically be converted to the specified encoding on output. If a file contains pure binary data (for instance, a JPEG image), the encoding for the channel should be configured to be binary. Tcl will then assign no interpretation to the data in the file and simply read or write raw bytes. The Tcl binary command can be usedto manipulate this byte-oriented data.
The default encoding for newly opened channels is thesame platform- and locale-dependent system encoding
used for interfacing with the operating system.-eofchar char
-eofchar {inChar outChar}
This option supports DOS file systems that useControl-z (\x1a) as an end of file marker. If char is
not an empty string, then this character signals end-
of-file when it is encountered during input. For out-
put, the end-of-file character is output when the chan-
nel is closed. If char is the empty string, then there Tcl Last change: 8.3 2Tcl Built-In Commands fconfigure(1T)
is no special end of file character marker. For read-
write channels, a two-element list specifies the end of
file marker for input and output, respectively. As aconvenience, when setting the end-of-file character for
a read-write channel you can specify a single value
that will apply to both reading and writing. Whenquerying the end-of-file character of a read-write
channel, a two-element list will always be returned.
The default value for -eofchar is the empty string in
all cases except for files under Windows. In that casethe -eofchar is Control-z (\x1a) for reading and the
empty string for writing.-translation mode
-translation {inMode outMode}
In Tcl scripts the end of a line is always represented using a single newline character (\n). However, in actual files and devices the end of a line may be represented differently on different platforms, or evenfor different devices on the same platform. For exam-
ple, under UNIX newlines are used in files, whereascarriage-return-linefeed sequences are normally used in
network connections. On input (i.e., with gets andread) the Tcl I/O system automatically translates the
external end-of-line representation into newline char-
acters. Upon output (i.e., with puts), the I/O system
translates newlines to the external end-of-line
representation. The default translation mode, auto, handles all the common cases automatically, but the-translation option provides explicit control over the
end of line translations.The value associated with -translation is a single item
for read-only and write-only channels. The value is a
two-element list for read-write channels; the read
translation mode is the first element of the list, and the write translation mode is the second element. As a convenience, when setting the translation mode for aread-write channel you can specify a single value that
will apply to both reading and writing. When queryingthe translation mode of a read-write channel, a two-
element list will always be returned. The following values are currently supported: auto As the input translation mode, auto treats any of newline (lf), carriage return (cr), or carriage return followed by a newline (crlf) as the end ofline representation. The end of line representa-
tion can even change from line-to-line, and all
cases are translated to a newline. As the output translation mode, auto chooses a platform specific Tcl Last change: 8.3 3Tcl Built-In Commands fconfigure(1T)
representation; for sockets on all platforms Tcl chooses crlf, for all Unix flavors, it chooses lf, for the Macintosh platform it chooses cr and for the various flavors of Windows it chooses crlf.The default setting for -translation is auto for
both input and output. binaryNo end-of-line translations are performed. This
is nearly identical to lf mode, except that inaddition binary mode also sets the end-of-file
character to the empty string (which disables it) and sets the encoding to binary (which disables encoding filtering). See the description of-eofchar and -encoding for more information.
Internally, i.e. when it comes to the actualbehaviour of the translator this value is identi-
cal to lf and is therefore reported as such whenqueried. Even if binary was used to set the trans-
lation. cr The end of a line in the underlying file or deviceis represented by a single carriage return charac-
ter. As the input translation mode, cr mode con-
verts carriage returns to newline characters. As the output translation mode, cr mode translates newline characters to carriage returns. This mode is typically used on Macintosh platforms. crlf The end of a line in the underlying file or deviceis represented by a carriage return character fol-
lowed by a linefeed character. As the inputtranslation mode, crlf mode converts carriage-
return-linefeed sequences to newline characters.
As the output translation mode, crlf modetranslates newline characters to carriage-return-
linefeed sequences. This mode is typically used on Windows platforms and for network connections. lf The end of a line in the underlying file or device is represented by a single newline (linefeed) character. In this mode no translations occurduring either input or output. This mode is typi-
cally used on UNIX platforms. STANDARD CHANNELS The Tcl standard channels (stdin, stdout, and stderr) can be configured through this command like every other channel opened by the Tcl library. Beyond the standard options described above they will also support any special option according to their current type. If, for example, a Tcl Tcl Last change: 8.3 4Tcl Built-In Commands fconfigure(1T)
application is started by the inet super-server common on
Unix system its Tcl standard channels will be sockets and thus support the socket options.EXAMPLES
Instruct Tcl to always send output to stdout immediately, whether or not it is to a terminal:fconfigure stdout -buffering none
Open a socket and read lines from it without ever blocking the processing of other events: set s [socket some.where.com 12345]fconfigure $s -blocking 0
fileevent $s readable "readMe $s"
proc readMe chan {if {[gets $chan line] < 0} {
if {[eof $chan]} {
close $chan
return }# Could not read a complete line this time; Tcl's
# internal buffering will hold the partial line for us
# until some more data is available over the socket.
} else {puts stdout $line
} }Read a PPM-format image from a file:
# Open the file and put it into Unix ASCII mode
set f [open teapot.ppm]fconfigure $f -encoding ascii -translation lf
# Get the header
if {[gets $f] ne "P6"} {
error "not a raw-bits PPM"
}# Read lines until we have got non-comment lines
# that supply us with three decimal values.
set words {}while {[llength $words] < 3} {
gets $f line
if {[string match "#*" $line]} continue
lappend words [eval concat [scan $line %d%d%d]]
}# Those words supply the size of the image and its
# overall depth per channel. Assign to variables.
foreach {xSize ySize depth} $words {break}
# Now switch to binary mode to pull in the data,
Tcl Last change: 8.3 5Tcl Built-In Commands fconfigure(1T)
# one byte per channel (red,green,blue) per pixel.
fconfigure $f -translation binary
set numDataBytes [expr {3 * $xSize * $ySize}]
set data [read $f $numDataBytes]
close $f
SEE ALSO
close(1T), flush(1T), gets(1T), open(1T), puts(1T),read(1T), socket(1T), Tcl_StandardChannels(3TCL)
KEYWORDS blocking, buffering, carriage return, end of line, flushing, linemode, newline, nonblocking, platform, translation, encoding, filter, byte array, binaryATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:_______________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE|
|____________________|__________________|_
| Availability | runtime/tcl-8 |
|____________________|__________________|_
| Interface Stability| Uncommitted ||____________________|_________________|
NOTES Source for Tcl is available on http://opensolaris.org. Tcl Last change: 8.3 6