tcl7.6 User Commands - puts
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 a channel identifier such
as returned from a previous invocation of open or socket. It
must have been opened for output. If no channelId is speci-
fied 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; on Macintoshes newlines
are normally replaced with carriage-returns). See the fcon-
figure manual entry for a discussion of end-of-line transla-
tions.
Tcl buffers output internally, so characters written with
puts may not appear immediately on the output file or dev-
ice; 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 nor-
mally block until all the buffered data has been accepted
for output by the operating system. If channelId is in non-
blocking 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 out-
put 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 chan-
nel 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 (don't invoke puts unless you have
recently been notified via a file event that the channel is
ready for more output data).
SEE ALSO
fileevent(n)
KEYWORDS
channel, newline, output, write