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fcopy(n) Tcl Built-In Commands fcopy(n)
__________________________________________________________________________________________________________________________________________________
NAME
fcopy - Copy data from one channel to another.
SYNOPSIS
fcopy inchan outchan ?-size size? ?-command callback?
_________________________________________________________________
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.
EXAMPLE
This first 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 second 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 -command [list CopyMore $in $out $chunk] -size $chunk
} } set in [open $file1] set out [socket $server $port] set chunk 1024 set total 0 fcopy $in $out -command [list CopyMore $in $out
$chunk] -size $chunk vwait done
SEE ALSO
eof(n), fblocked(n), fconfigure(n)
KEYWORDS
blocking, channel, end of line, end of file, nonblocking, read, translation
Tcl 8.0 fcopy(n)