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.  Chan-
       nelId identifies the channel for which to set or query an  option.   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 intially 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-

              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, 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- |

              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-

              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.

       close(n), flush(n), gets(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                                   8.1                        fconfigure(n)