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puts(3tcl) Tcl Built-In Commands puts(3tcl) 





NAME


puts - Write to a channel






SYNOPSIS


puts ?-nonewline? ?channelId?
  string








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







  

    7.5
    Tcl