fcopy(n)						       Tcl Built-In Commands							  fcopy(n)

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NAME

       fcopy - Copy data from one channel to another

SYNOPSIS

       fcopy inchan outchan ?-size size? ?-command callback?
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DESCRIPTION

       The  fcopy  command copies data from one I/O channel, inchan to another I/O channel, outchan.  The fcopy command leverages the buffering in
       the Tcl I/O system to avoid extra copies and to avoid buffering too much data in main memory when copying large files to slow  destinations
       like network sockets.

       The fcopy command transfers data from inchan until end of file or size bytes have been transferred. If no -size argument is given, then the
       copy goes until end of file.  All the data read from inchan is copied to outchan.  Without the -command option, fcopy blocks until the copy
       is complete and returns the number of bytes written to outchan.

       The  -command  argument makes fcopy work in the background.  In this case it returns immediately and the callback is invoked later when the
       copy completes.	The callback is called with one or two additional arguments that indicates how many bytes were written to outchan.  If	an
       error  occurred	during the background copy, the second argument is the error string associated with the error.	With a background copy, it
       is not necessary to put inchan or outchan into non-blocking mode; the fcopy command takes care of that automatically.  However, it is  nec-
       essary to enter the event loop by using the vwait command or by using Tk.

       You  are  not  allowed to do other I/O operations with inchan or outchan during a background fcopy.  If either inchan or outchan get closed
       while the copy is in progress, the current copy is stopped and the command callback is not made.   If  inchan  is  closed,  then  all  data
       already queued for outchan is written out.

       Note  that  inchan  can	become	readable during a background copy.  You should turn off any fileevent handlers during a background copy so
       those handlers do not interfere with the copy.  Any I/O attempted by a fileevent handler will get a "channel busy" error.

       Fcopy translates end-of-line sequences in inchan and outchan according to the -translation option for these channels.  See the manual entry
       for  fconfigure	for  details on the -translation option.  The translations mean that the number of bytes read from inchan can be different
       than the number of bytes written to outchan.  Only the number of bytes written to outchan is reported, either as the return value of a syn-
       chronous fcopy or as the argument to the callback for an asynchronous fcopy.

       Fcopy  obeys  the  encodings  and character translations configured for the channels. This means that the incoming characters are converted
       internally first UTF-8 and then into the encoding of the channel fcopy writes to. See the manual entry for fconfigure for  details  on  the
       -encoding  and -translation options. No conversion is done if both channels are set to encoding "binary" and have matching translations. If
       only the output channel is set to encoding "binary" the system will write the internal UTF-8 representation of the incoming characters.	If
       only  the  input  channel is set to encoding "binary" the system will assume that the incoming bytes are valid UTF-8 characters and convert
       them according to the output encoding. The behaviour of the system for bytes which are not valid UTF-8  characters  is  undefined  in  this
       case.

EXAMPLES

       The first example transfers the contents of one channel exactly to another. Note that when copying one file to another, it is better to use
       file copy which also copies file metadata (e.g. the file access permissions) where possible.
	      fconfigure $in -translation binary
	      fconfigure $out -translation binary
	      fcopy $in $out

       This second example shows how the callback gets passed the number of bytes transferred.	It also uses vwait to put the application into the
       event loop.  Of course, this simplified example could be done without the command callback.
	      proc Cleanup {in out bytes {error {}}} {
		  global total
		  set total $bytes
		  close $in
		  close $out
		  if {[string length $error] != 0} {
		# error occurred during the copy
		  }
	      }
	      set in [open $file1]
	      set out [socket $server $port]
	      fcopy $in $out -command [list Cleanup $in $out]
	      vwait total

       The third example copies in chunks and tests for end of file in the command callback
	      proc CopyMore {in out chunk bytes {error {}}} {
		  global total done
		  incr total $bytes
		  if {([string length $error] != 0) || [eof $in]} {
		set done $total
		close $in
		close $out
		  } else {
		fcopy $in $out -size $chunk 
			      -command [list CopyMore $in $out $chunk]
		  }
	      }
	      set in [open $file1]
	      set out [socket $server $port]
	      set chunk 1024
	      set total 0
	      fcopy $in $out -size $chunk 
		      -command [list CopyMore $in $out $chunk]
	      vwait done

SEE ALSO

       eof(n), fblocked(n), fconfigure(n), file(n)

KEYWORDS

       blocking, channel, end of line, end of file, nonblocking, read, translation

Tcl									8.0								  fcopy(n)