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 de‐
38       vices.
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  de‐
48              tails.   For nonblocking mode to work correctly, the application
49              must be using the Tcl event loop (e.g. by calling Tcl_DoOneEvent
50              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  in‐
55              voked.  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 im‐
82              age), 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  er‐
114              ror.
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 de‐
121              vices  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.
156
157              binary No  end-of-line  translations  are  performed.   This  is
158                     nearly identical to lf mode, except that in addition  bi‐
159                     nary  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 de‐
162                     scription of -eofchar and -encoding for more information.
163
164                     Internally, i.e. when it comes to the actual behaviour of
165                     the  translator  this  value  is  identical  to lf and is
166                     therefore reported as such when queried. Even  if  binary
167                     was used to set the translation.
168
169              cr     The  end  of  a  line in the underlying file or device is
170                     represented by a single carriage  return  character.   As
171                     the input translation mode, cr mode converts carriage re‐
172                     turns to newline characters.  As the  output  translation
173                     mode,  cr  mode translates newline characters to carriage
174                     returns.
175
176              crlf   The end of a line in the underlying  file  or  device  is
177                     represented  by a carriage return character followed by a
178                     linefeed character.  As the input translation mode,  crlf
179                     mode  converts carriage-return-linefeed sequences to new‐
180                     line characters.  As the output  translation  mode,  crlf
181                     mode  translates  newline  characters to carriage-return-
182                     linefeed sequences.  This mode is typically used on  Win‐
183                     dows platforms and for network connections.
184
185              lf     The  end  of  a  line in the underlying file or device is
186                     represented by a single newline (linefeed) character.  In
187                     this  mode  no  translations occur during either input or
188                     output.  This mode is typically used on UNIX platforms.
189

STANDARD CHANNELS

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

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

258       close(n), flush(n),  gets(n),  open(n),  puts(n),  read(n),  socket(n),
259       Tcl_StandardChannels(3)
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KEYWORDS

262       blocking,  buffering, carriage return, end of line, flushing, linemode,
263       newline, nonblocking, platform, translation, encoding, filter, byte ar‐
264       ray, binary
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268Tcl                                   8.3                        fconfigure(n)
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