Provided by: tcl8.5-doc_8.5.19-1_all 
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 channels.
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 given option. If one or more pairs of name and value are supplied, 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 indefinitely. 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 by allowing them to operate
asynchronously; see the documentation for those commands for details. For nonblocking mode to
work correctly, the application must be using the Tcl event loop (e.g. by calling Tcl_DoOneEvent
or invoking the vwait command).
-buffering newValue
If newValue is full then the I/O system will buffer output until its internal buffer is full or
until the flush command is invoked. If newValue is line, then the I/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 automatically 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 is also 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 used to manipulate this byte-
oriented data. It is usually better to set the -translation option to binary when you want to
transfer binary data, as this turns off the other automatic interpretations of the bytes in the
stream as well.
The default encoding for newly opened channels is the same platform- and locale-dependent system
encoding used for interfacing with the operating system, as returned by encoding system.
-eofchar char
-eofchar {inChar outChar}
This option supports DOS file systems that use Control-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 output, the end-of-file character is output when the channel is closed. If char is
the empty string, then there 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 a
convenience, 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. When querying 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 case the
-eofchar is Control-z (\x1a) for reading and the empty string for writing. The acceptable range
for -eofchar values is \x01 - \x7f; attempting to set -eofchar to a value outside of this range
will generate an error.
-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 even for different devices on the same platform. For example, under UNIX newlines
are used in files, whereas carriage-return-linefeed sequences are normally used in network
connections. On input (i.e., with gets and read) the Tcl I/O system automatically translates the
external end-of-line representation into newline characters. 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 a read-write channel you can specify a single value that will
apply to both reading and writing. When querying the 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 of line representation. The end of
line representation 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 representation;
for sockets on all platforms Tcl chooses crlf, for all Unix flavors, it chooses lf, and for
the various flavors of Windows it chooses crlf. The default setting for -translation is
auto for both input and output.
binary No end-of-line translations are performed. This is nearly identical to lf mode, except
that in addition 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 actual behaviour of the translator this value is
identical to lf and is therefore reported as such when queried. Even if binary was used to
set the translation.
cr The end of a line in the underlying file or device is represented by a single carriage
return character. As the input translation mode, cr mode converts carriage returns to
newline characters. As the output translation mode, cr mode translates newline characters
to carriage returns.
crlf The end of a line in the underlying file or device is represented by a carriage return
character followed by a linefeed character. As the input translation mode, crlf mode
converts carriage-return-linefeed sequences to newline characters. As the output
translation mode, crlf mode translates 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 occur during either input or output.
This mode is typically 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 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 {*}[join [scan $line %d%d%d]]
}
# Those words supply the size of the image and its
# overall depth per channel. Assign to variables.
lassign $words xSize ySize depth
# Now switch to binary mode to pull in the data,
# 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(3tcl), flush(3tcl), gets(3tcl), open(3tcl), puts(3tcl), read(3tcl), socket(3tcl),
Tcl_StandardChannels(3tcl)
KEYWORDS
blocking, buffering, carriage return, end of line, flushing, linemode, newline, nonblocking, platform,
translation, encoding, filter, byte array, binary