puts - Online Linux Manual Page

Section : n
Updated : 7.5
Source : Tcl
Note : Tcl Built-In Commands

NAME

puts − 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 an identifier for an open channel such as a Tcl standard channel (

stdout

stderr

), the return value from an invocation of

open

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 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 (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