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puts(3tcl)


NAME

   puts - Write to a channel

SYNOPSIS

   puts ?-nonewline? ?channelId? string
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DESCRIPTION

   Writes  the  characters  given  by  string  to  the  channel  given  by
   channelId.

   ChannelId must be an identifier for an  open  channel  such  as  a  Tcl
   standard   channel  (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. The channel must have been opened
   for output.

   If no channelId is specified then it defaults to stdout. Puts  normally
   outputs  a  newline  character  after  string,  but this feature may be
   suppressed by specifying the -nonewline switch.

   Newline characters in the output are translated by  puts  to  platform-
   specific  end-of-line  sequences  according to the current value of the
   -translation option for the channel (for example, on PCs  newlines  are
   normally  replaced  with  carriage-return-linefeed  sequences.  See the
   fconfigure manual entry for a discussion on ways  in  which  fconfigure
   will alter output.

   Tcl  buffers output internally, so characters written with puts may not
   appear immediately on the output file or  device;   Tcl  will  normally
   delay  output  until  the buffer is full or the channel is closed.  You
   can force output to appear immediately with the flush command.

   When the output buffer fills up, the puts command will  normally  block
   until  all  the  buffered  data  has  been  accepted  for output by the
   operating system.  If channelId is in nonblocking mode  then  the  puts
   command  will  not block even if the operating system cannot accept the
   data.  Instead, Tcl continues to buffer the data and writes it  in  the
   background as fast as the underlying file or device can accept it.  The
   application must use the Tcl event loop for nonblocking output to work;
   otherwise Tcl never finds out that the file or device is ready for more
   output data.  It is possible for an arbitrarily large amount of data to
   be  buffered  for  a channel in nonblocking mode, which could consume a
   large amount of memory.   To  avoid  wasting  memory,  nonblocking  I/O
   should  normally  be used in an event-driven fashion with the fileevent
   command (do not invoke puts unless you have recently been notified  via
   a file event that the channel is ready for more output data).

EXAMPLES

   Write a short message to the console (or wherever stdout is directed):
          puts "Hello, World!"

   Print a message in several parts:
          puts -nonewline "Hello, "
          puts "World!"

   Print a message to the standard error channel:
          puts stderr "Hello, World!"

   Append a log message to a file:
          set chan [open my.log a]
          set timestamp [clock format [clock seconds]]
          puts $chan "$timestamp - Hello, World!"
          close $chan

SEE ALSO

   file(3tcl), fileevent(3tcl), Tcl_StandardChannels(3tcl)

KEYWORDS

   channel, newline, output, write



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