1fconfigure(n)                Tcl Built-In Commands               fconfigure(n)
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NAME

8       fconfigure - Set and get options on a channel
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SYNOPSIS

11       fconfigure channelId
12       fconfigure channelId name
13       fconfigure channelId name value ?name value ...?
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DESCRIPTION

17       The fconfigure command sets and retrieves options for channels.
18
19       ChannelId  identifies  the  channel for which to set or query an option
20       and must refer to an open  channel  such  as  a  Tcl  standard  channel
21       (stdin, stdout, or stderr), the return value from an invocation of open
22       or socket, or the result of a channel creation command  provided  by  a
23       Tcl extension.
24
25       If  no name or value arguments are supplied, the command returns a list
26       containing alternating option names and values  for  the  channel.   If
27       name  is  supplied  but  no  value then the command returns the current
28       value of the given option.  If one or more pairs of name and value  are
29       supplied, the command sets each of the named options to the correspond‐
30       ing value; in this case the return value is an empty string.
31
32       The options described below are supported for all  channels.  In  addi‐
33       tion,  each channel type may add options that only it supports. See the
34       manual entry for the command that creates each type of channels for the
35       options  that  that specific type of channel supports. For example, see
36       the manual entry for the socket  command  for  additional  options  for
37       sockets,  and  the  open  command  for  additional  options  for serial
38       devices.
39
40       -blocking boolean
41              The -blocking option determines whether I/O  operations  on  the
42              channel  can cause the process to block indefinitely.  The value
43              of the option must be a proper boolean value.  Channels are nor‐
44              mally in blocking mode;  if a channel is placed into nonblocking
45              mode it will affect the  operation  of  the  gets,  read,  puts,
46              flush,  and  close  commands  by  allowing them to operate asyn‐
47              chronously;  see  the  documentation  for  those  commands   for
48              details.   For  nonblocking mode to work correctly, the applica‐
49              tion  must  be  using  the  Tcl  event  loop  (e.g.  by  calling
50              Tcl_DoOneEvent or invoking the vwait command).
51
52       -buffering newValue
53              If newValue is full then the I/O system will buffer output until
54              its internal buffer is  full  or  until  the  flush  command  is
55              invoked. If newValue is line, then the I/O system will automati‐
56              cally flush output for the channel whenever a newline  character
57              is  output. If newValue is none, the I/O system will flush auto‐
58              matically after every output  operation.   The  default  is  for
59              -buffering to be set to full except for channels that connect to
60              terminal-like devices; for these channels the initial setting is
61              line.  Additionally, stdin and stdout are initially set to line,
62              and stderr is set to none.
63
64       -buffersize newSize
65              Newvalue must be an integer; its value is used to set  the  size
66              of buffers, in bytes, subsequently allocated for this channel to
67              store input or output. Newvalue must be between one and one mil‐
68              lion, allowing buffers of one to one million bytes in size.
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70       -encoding name
71              This  option  is used to specify the encoding of the channel, so
72              that the data can be converted to and from Unicode  for  use  in
73              Tcl.   For  instance, in order for Tcl to read characters from a
74              Japanese file in shiftjis and properly process and  display  the
75              contents,  the  encoding  would be set to shiftjis.  Thereafter,
76              when reading from the channel, the bytes in  the  Japanese  file
77              would be converted to Unicode as they are read.  Writing is also
78              supported - as Tcl strings are written to the channel they  will
79              automatically be converted to the specified encoding on output.
80
81              If  a  file  contains  pure  binary  data  (for instance, a JPEG
82              image), the encoding for the channel should be configured to  be
83              binary.   Tcl  will then assign no interpretation to the data in
84              the file and simply read or write raw  bytes.   The  Tcl  binary
85              command  can  be used to manipulate this byte-oriented data.  It
86              is usually better to set the -translation option to binary  when
87              you  want  to  transfer binary data, as this turns off the other
88              automatic interpretations of the bytes in the stream as well.
89
90              The default encoding for newly opened channels is the same plat‐
91              form-  and locale-dependent system encoding used for interfacing
92              with the operating system, as returned by encoding system.
93
94       -eofchar char
95
96       -eofchar {inChar outChar}
97              This option supports DOS file systems that use Control-z  (\x1a)
98              as  an end of file marker.  If char is not an empty string, then
99              this character signals end-of-file when it is encountered during
100              input.  For output, the end-of-file character is output when the
101              channel is closed.  If char is the empty string, then  there  is
102              no  special  end of file character marker.  For read-write chan‐
103              nels, a two-element list specifies the end of  file  marker  for
104              input  and output, respectively.  As a convenience, when setting
105              the end-of-file character for a read-write channel you can spec‐
106              ify  a single value that will apply to both reading and writing.
107              When querying the end-of-file character of a read-write channel,
108              a  two-element  list will always be returned.  The default value
109              for -eofchar is the empty string in all cases except  for  files
110              under  Windows.   In  that case the -eofchar is Control-z (\x1a)
111              for reading and the empty string for  writing.   The  acceptable
112              range  for  -eofchar  values  is  \x01 - \x7f; attempting to set
113              -eofchar to a value outside  of  this  range  will  generate  an
114              error.
115
116       -translation mode
117
118       -translation {inMode outMode}
119              In  Tcl  scripts the end of a line is always represented using a
120              single newline character (\n).  However,  in  actual  files  and
121              devices the end of a line may be represented differently on dif‐
122              ferent platforms, or even for  different  devices  on  the  same
123              platform.   For  example, under UNIX newlines are used in files,
124              whereas carriage-return-linefeed sequences are normally used  in
125              network  connections.   On  input (i.e., with gets and read) the
126              Tcl I/O system automatically translates the external end-of-line
127              representation into newline characters.  Upon output (i.e., with
128              puts), the I/O system translates newlines to the  external  end-
129              of-line  representation.   The  default  translation mode, auto,
130              handles all the common cases automatically, but the -translation
131              option  provides  explicit control over the end of line transla‐
132              tions.
133
134              The value associated with -translation  is  a  single  item  for
135              read-only  and  write-only channels.  The value is a two-element
136              list for read-write channels; the read translation mode  is  the
137              first element of the list, and the write translation mode is the
138              second element.  As a convenience, when setting the  translation
139              mode  for  a  read-write  channel you can specify a single value
140              that will apply to both reading and writing.  When querying  the
141              translation  mode  of  a  read-write channel, a two-element list
142              will always be returned.  The  following  values  are  currently
143              supported:
144
145              auto   As the input translation mode, auto treats any of newline
146                     (lf), carriage return (cr), or carriage  return  followed
147                     by  a  newline  (crlf) as the end of line representation.
148                     The end of line representation can even change from line-
149                     to-line,  and  all cases are translated to a newline.  As
150                     the output translation mode, auto chooses a platform spe‐
151                     cific  representation;  for  sockets on all platforms Tcl
152                     chooses crlf, for all Unix flavors, it  chooses  lf,  and
153                     for  the various flavors of Windows it chooses crlf.  The
154                     default setting for -translation is auto for  both  input
155                     and output.
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157              binary No  end-of-line  translations  are  performed.   This  is
158                     nearly identical to lf  mode,  except  that  in  addition
159                     binary  mode  also  sets the end-of-file character to the
160                     empty string (which disables it) and sets the encoding to
161                     binary  (which  disables  encoding  filtering).   See the
162                     description of -eofchar and -encoding for  more  informa‐
163                     tion.
164
165                     Internally, i.e. when it comes to the actual behaviour of
166                     the translator this value  is  identical  to  lf  and  is
167                     therefore  reported  as such when queried. Even if binary
168                     was used to set the translation.
169
170              cr     The end of a line in the underlying  file  or  device  is
171                     represented  by  a  single carriage return character.  As
172                     the input translation mode,  cr  mode  converts  carriage
173                     returns to newline characters.  As the output translation
174                     mode, cr mode translates newline characters  to  carriage
175                     returns.
176
177              crlf   The  end  of  a  line in the underlying file or device is
178                     represented by a carriage return character followed by  a
179                     linefeed  character.  As the input translation mode, crlf
180                     mode converts carriage-return-linefeed sequences to  new‐
181                     line  characters.   As  the output translation mode, crlf
182                     mode translates newline  characters  to  carriage-return-
183                     linefeed  sequences.  This mode is typically used on Win‐
184                     dows platforms and for network connections.
185
186              lf     The end of a line in the underlying  file  or  device  is
187                     represented by a single newline (linefeed) character.  In
188                     this mode no translations occur during  either  input  or
189                     output.  This mode is typically used on UNIX platforms.
190

STANDARD CHANNELS

192       The Tcl standard channels (stdin, stdout, and stderr) can be configured
193       through this command  like  every  other  channel  opened  by  the  Tcl
194       library.  Beyond  the  standard  options described above they will also
195       support any special option according to their current  type.   If,  for
196       example,  a  Tcl application is started by the inet super-server common
197       on Unix system its Tcl standard channels will be sockets and thus  sup‐
198       port the socket options.
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EXAMPLES

201       Instruct  Tcl  to  always send output to stdout immediately, whether or
202       not it is to a terminal:
203
204              fconfigure stdout -buffering none
205
206       Open a socket and read lines from it without ever blocking the process‐
207       ing of other events:
208
209              set s [socket some.where.com 12345]
210              fconfigure $s -blocking 0
211              fileevent $s readable "readMe $s"
212              proc readMe chan {
213                  if {[gets $chan line] < 0} {
214                      if {[eof $chan]} {
215                          close $chan
216                          return
217                      }
218                      # Could not read a complete line this time; Tcl's
219                      # internal buffering will hold the partial line for us
220                      # until some more data is available over the socket.
221                  } else {
222                      puts stdout $line
223                  }
224              }
225
226       Read a PPM-format image from a file:
227
228              # Open the file and put it into Unix ASCII mode
229              set f [open teapot.ppm]
230              fconfigure $f -encoding ascii -translation lf
231
232              # Get the header
233              if {[gets $f] ne "P6"} {
234                  error "not a raw-bits PPM"
235              }
236
237              # Read lines until we have got non-comment lines
238              # that supply us with three decimal values.
239              set words {}
240              while {[llength $words] < 3} {
241                  gets $f line
242                  if {[string match "#*" $line]} continue
243                  lappend words {*}[join [scan $line %d%d%d]]
244              }
245
246              # Those words supply the size of the image and its
247              # overall depth per channel. Assign to variables.
248              lassign $words xSize ySize depth
249
250              # Now switch to binary mode to pull in the data,
251              # one byte per channel (red,green,blue) per pixel.
252              fconfigure $f -translation binary
253              set numDataBytes [expr {3 * $xSize * $ySize}]
254              set data [read $f $numDataBytes]
255
256              close $f
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SEE ALSO

259       close(n),  flush(n),  gets(n),  open(n),  puts(n),  read(n), socket(n),
260       Tcl_StandardChannels(3)
261

KEYWORDS

263       blocking, buffering, carriage return, end of line, flushing,  linemode,
264       newline,  nonblocking,  platform,  translation,  encoding, filter, byte
265       array, binary
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269Tcl                                   8.3                        fconfigure(n)
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