x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
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 or characters have been transferred; size is in bytes if the two
channels are using the same encoding, and is in characters otherwise.
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 -com-
mand option, fcopy blocks until the copy is complete and returns the
number of bytes or characters (using the same rules as for the -size
option) 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 oc-
curred 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 necessary to
enter the event loop by using the vwait command or by using Tk.
You are not allowed to do other input operations with inchan, or output
operations with outchan, during a background fcopy. The converse is en-
tirely legitimate, as exhibited by the bidirectional fcopy example be-
low.
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 wrong-sided I/O at-
tempted (by a fileevent handler or otherwise) 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 transla-
tions 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 inter-
nally first UTF-8 and then into the encoding of the channel fcopy
writes to. See the manual entry for fconfigure for details on the -en-
coding 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 ac-
cording 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 an-
other. 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 permis-
sions) 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 $chunk]
vwait done
The fourth example starts an asynchronous, bidirectional fcopy between
two sockets. Those could also be pipes from two [open "|hal 9000" r+]
(though their conversation would remain secret to the script, since all
four fileevent slots are busy).
set flows 2
proc Done {dir args} {
global flows done
puts "$dir is over."
incr flows -1
if {$flows<=0} {set done 1}
}
fcopy $sok1 $sok2 -command [list Done UP]
fcopy $sok2 $sok1 -command [list Done DOWN]
vwait done
SEE ALSO
eof(n), fblocked(n), fconfigure(n), file(n)
KEYWORDS
blocking, channel, end of line, end of file, nonblocking, read, trans-
lation
Tcl 8.0 fcopy(n)
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