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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 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 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; see the documentation for those com‐
	      mands 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 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 ten and one mil‐
	      lion, 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.

	      The default encoding for newly opened channels is the same plat‐
	      form-  and locale-dependent system encoding used for interfacing
	      with the operating 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.

       -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 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, 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.

	      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 informa‐
		     tion.

		     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.  This mode is typically used on Macintosh	 plat‐
		     forms.

	      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
       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  sup‐
       port 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 [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,
	      # 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
       array, binary

Tcl				      8.3			 fconfigure(n)
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