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fconfigure(n)		     Tcl Built-In Commands		 fconfigure(n)

______________________________________________________________________________

NAME
       fconfigure - Set	and get	options	on a channel

SYNOPSIS
       fconfigure channelId
       fconfigure channelId name
       fconfigure channelId name value ?name value ...?
______________________________________________________________________________

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 correspond-
       ing value; in this case the return value	is an empty string.

       The options described below are supported for all  channels.  In	 addi-
       tion,  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  additional  options  for
       sockets,	 and  the  open	 command for additional	options	for serial de-
       vices.

       -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 nor-
	      mally 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 asyn-
	      chronously; see the documentation	for  those  commands  for  de-
	      tails.   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  in-
	      voked.  If  newValue is line, then the I/O system	will automati-
	      cally flush output for the channel whenever a newline  character
	      is  output. If newValue is none, the I/O system will flush auto-
	      matically	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 one and one mil-
	      lion, allowing buffers of	one 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 im-
	      age), 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 plat-
	      form-  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 chan-
	      nels, 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 spec-
	      ify  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  er-
	      ror.

       -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 de-
	      vices  the  end of a line	may be represented differently on dif-
	      ferent 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 transla-
	      tions.

	      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 spe-
		     cific  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  bi-
		     nary  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 de-
		     scription 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 re-
		     turns 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 new-
		     line characters.  As the output  translation  mode,  crlf
		     mode  translates  newline	characters to carriage-return-
		     linefeed sequences.  This mode is typically used on  Win-
		     dows 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 li-
       brary. Beyond the standard options described above they will also  sup-
       port any	special	option according to their current type.	 If, for exam-
       ple, 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 process-
       ing 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(n), flush(n),  gets(n),  open(n),	puts(n),  read(n),  socket(n),
       Tcl_StandardChannels(3)

KEYWORDS
       blocking,  buffering, carriage return, end of line, flushing, linemode,
       newline,	nonblocking, platform, translation, encoding, filter, byte ar-
       ray, binary

Tcl				      8.3			 fconfigure(n)

NAME | SYNOPSIS | DESCRIPTION | STANDARD CHANNELS | EXAMPLES | SEE ALSO | KEYWORDS

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