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man pages section 1: User Commands

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Updated: Wednesday, February 9, 2022

puts (1t)


puts - Write to a channel


puts ?-nonewline? ?channelId? string


puts(1t)                     Tcl Built-In Commands                    puts(1t)


       puts - Write to a channel

       puts ?-nonewline? ?channelId? string

       Writes  the  characters  given  by string to the channel given by chan-

       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).

       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 attributes(7) for descriptions of the following attributes:

       |Availability   | runtime/tcl-8    |
       |Stability      | Uncommitted      |

       file(n), fileevent(n), Tcl_StandardChannels(3)

       channel, newline, output, write

       Source code for open source software components in Oracle  Solaris  can
       be found at https://www.oracle.com/downloads/opensource/solaris-source-

       This    software    was    built    from    source     available     at
       https://github.com/oracle/solaris-userland.    The  original  community
       source was downloaded from  http://prdownloads.sourceforge.net/tcl/tcl-

       Further information about this software can be found on the open source
       community website at https://www.tcl.tk/.

Tcl                                   7.5                             puts(1t)