puts(n) Tcl Built-In Commands puts(n)
NAME
puts - Write to a channel
SYNOPSIS
puts ?-nonewline? ?channelId? string
DESCRIPTION
Writes the characters given by string to the channel given by chan-
nelId.
ChannelId must be an identifier for an open channel such as a Tcl stan-
dard 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 sup-
pressed 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 operat-
ing 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 back-
ground 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(n), fileevent(n), Tcl_StandardChannels(3)
KEYWORDS
channel, newline, output, write
Tcl 7.5 puts(n)
tcl 8.6.0 - Generated Thu Jan 10 15:38:40 CST 2013