fconfigure man page on Archlinux

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


       fconfigure - Set and get options on a channel

       fconfigure channelId
       fconfigure channelId name
       fconfigure channelId name value ?name value ...?

       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

       -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
	      details.	 For  nonblocking mode to work correctly, the applica‐
	      tion  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 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
	      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 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

       -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‐

	      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

	      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
		     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‐

		     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

	      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.

       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.

       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
		      # 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

       close(n),  flush(n),  gets(n),  open(n),	 puts(n),  read(n), socket(n),

       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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