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 new-lines newlines
lines 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 on ways
in which fconfigure will alter output.
Tcl buffers output internally, so characters written with puts may not appear immediately on the out-put output
put 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 con-sume consume
sume 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
file(n), fileevent(n), Tcl_StandardChannels(3)
KEYWORDS
channel, newline, output, write
Tcl 7.5 puts(n)
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