puts (n)
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 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).
SEE ALSO
KEYWORDS
channel, newline, output, write
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