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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
       devices.

       -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
              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 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
                     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.

              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 {*}[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 num-
       DataBytes [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)

tcl 8.6.1 - Generated Mon Sep 30 16:45:28 CDT 2013
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