puts(n) Tcl (7.5) puts(n)
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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 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
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; on Macintoshes newlines
are normally replaced with carriage-returns). See the
fconfigure manual entry for a discussion of end-of-line
translations.
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 (don't invoke puts unless
you have recently been notified via a file event that the
channel is ready for more output data).
Page 1 (printed 2/19/99)
puts(n) Tcl (7.5) puts(n)
SEE ALSO
fileevent(n)
KEYWORDS
channel, newline, output, write
Page 2 (printed 2/19/99)
