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puts(n) Tcl Built-In Commands 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 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 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)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
On Apache/2.4.6 (CentOS)
Under GNU General Public License
2025-06-23 22:04 @127.0.0.1 CrawledBy Wget/1.21.2