59 lines
3.3 KiB
HTML
59 lines
3.3 KiB
HTML
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<HTML><HEAD><TITLE>Tcl Built-In Commands - puts manual page</TITLE></HEAD><BODY>
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<H3><A NAME="M2">NAME</A></H3>
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puts - Write to a channel
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<H3><A NAME="M3">SYNOPSIS</A></H3>
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<B>puts </B>?<B>-nonewline</B>? ?<I>channelId</I>? <I>string</I><BR>
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<H3><A NAME="M4">DESCRIPTION</A></H3>
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Writes the characters given by <I>string</I> to the channel given
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by <I>channelId</I>.
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<I>ChannelId</I> must be a channel identifier such as returned from a
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previous invocation of <B><A HREF="../TkCmd/open.htm">open</A></B> or <B><A HREF="../TkCmd/socket.htm">socket</A></B>. It must have been opened
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for output. If no <I>channelId</I> is specified then it defaults to
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<B>stdout</B>. <B>Puts</B> normally outputs a newline character after
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<I>string</I>, but this feature may be suppressed by specifying the
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<B>-nonewline</B> switch.
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<P>
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Newline characters in the output are translated by <B>puts</B> to
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platform-specific end-of-line sequences according to the current
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value of the <B>-translation</B> option for the channel (for example,
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on PCs newlines are normally replaced with carriage-return-linefeed
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sequences; on Macintoshes newlines are normally replaced with
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carriage-returns).
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See the <B><A HREF="../TkCmd/fconfigure.htm">fconfigure</A></B> manual entry for a discussion on ways in
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which <B><A HREF="../TkCmd/fconfigure.htm">fconfigure</A></B> will alter output.
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<P>
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Tcl buffers output internally, so characters written with <B>puts</B>
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may not appear immediately on the output file or device; Tcl will
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normally delay output until the buffer is full or the channel is
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closed.
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You can force output to appear immediately with the <B><A HREF="../TkCmd/flush.htm">flush</A></B>
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command.
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<P>
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When the output buffer fills up, the <B>puts</B> command will normally
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block until all the buffered data has been accepted for output by the
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operating system.
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If <I>channelId</I> is in nonblocking mode then the <B>puts</B> command
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will not block even if the operating system cannot accept the data.
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Instead, Tcl continues to buffer the data and writes it in the
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background as fast as the underlying file or device can accept it.
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The application must use the Tcl event loop for nonblocking output
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to work; otherwise Tcl never finds out that the file or device is
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ready for more output data.
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It is possible for an arbitrarily large amount of data to be
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buffered for a channel in nonblocking mode, which could consume a
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large amount of memory.
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To avoid wasting memory, nonblocking I/O should normally
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be used in an event-driven fashion with the <B><A HREF="../TkCmd/fileevent.htm">fileevent</A></B> command
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(don't invoke <B>puts</B> unless you have recently been notified
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via a file event that the channel is ready for more output data).
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<H3><A NAME="M5">SEE ALSO</A></H3>
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<B><A HREF="../TkCmd/file.htm">file</A></B>, <B><A HREF="../TkCmd/fileevent.htm">fileevent</A></B>
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<H3><A NAME="M6">KEYWORDS</A></H3>
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<A href="../Keywords/C.htm#channel">channel</A>, <A href="../Keywords/N.htm#newline">newline</A>, <A href="../Keywords/O.htm#output">output</A>, <A href="../Keywords/W.htm#write">write</A>
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<HR><PRE>
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<A HREF="../copyright.htm">Copyright</A> © 1993 The Regents of the University of California.
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<A HREF="../copyright.htm">Copyright</A> © 1994-1996 Sun Microsystems, Inc.
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<A HREF="../copyright.htm">Copyright</A> © 1995-1997 Roger E. Critchlow Jr.</PRE>
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</BODY></HTML>
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