1fcopy(n) Tcl Built-In Commands fcopy(n)
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8 fcopy - Copy data from one channel to another.
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11 fcopy inchan outchan ?-size size? ?-command callback?
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16 The fcopy command copies data from one I/O channel, inchan to another
17 I/O channel, outchan. The fcopy command leverages the buffering in the
18 Tcl I/O system to avoid extra copies and to avoid buffering too much
19 data in main memory when copying large files to slow destinations like
20 network sockets.
21 The fcopy command transfers data from inchan until end of file or size
23 bytes have been transferred. If no -size argument is given, then the
24 copy goes until end of file. All the data read from inchan is copied
25 to outchan. Without the -command option, fcopy blocks until the copy
26 is complete and returns the number of bytes written to outchan.
27 The -command argument makes fcopy work in the background. In this case
29 it returns immediately and the callback is invoked later when the copy
30 completes. The callback is called with one or two additional arguments
31 that indicates how many bytes were written to outchan. If an error
32 occurred during the background copy, the second argument is the error
33 string associated with the error. With a background copy, it is not
34 necessary to put inchan or outchan into non-blocking mode; the fcopy
35 command takes care of that automatically. However, it is necessary to
36 enter the event loop by using the vwait command or by using Tk.
37 You are not allowed to do other I/O operations with inchan or outchan
39 during a background fcopy. If either inchan or outchan get closed
40 while the copy is in progress, the current copy is stopped and the com‐
41 mand callback is not made. If inchan is closed, then all data already
42 queued for outchan is written out.
43 Note that inchan can become readable during a background copy. You
45 should turn off any fileevent handlers during a background copy so
46 those handlers do not interfere with the copy. Any I/O attempted by a
47 fileevent handler will get a "channel busy" error.
48 Fcopy translates end-of-line sequences in inchan and outchan according
50 to the -translation option for these channels. See the manual entry
51 for fconfigure for details on the -translation option. The transla‐
52 tions mean that the number of bytes read from inchan can be different
53 than the number of bytes written to outchan. Only the number of bytes
54 written to outchan is reported, either as the return value of a syn‐
55 chronous fcopy or as the argument to the callback for an asynchronous
56 fcopy.
57 Fcopy obeys the encodings configured for the channels. This means that
59 the incoming characters are converted internally first UTF-8 and then
60 into the encoding of the channel fcopy writes to. See the manual entry
61 for fconfigure for details on the -encoding option. No conversion is
62 done if both channels are set to encoding "binary". If only the output
63 channel is set to encoding "binary" the system will write the internal
64 UTF-8 representation of the incoming characters. If only the input
65 channel is set to encoding "binary" the system will assume that the
66 incoming bytes are valid UTF-8 characters and convert them according to
67 the output encoding. The behaviour of the system for bytes which are
68 not valid UTF-8 characters is undefined in this case.
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72 This first example shows how the callback gets passed the number of
73 bytes transferred. It also uses vwait to put the application into the
74 event loop. Of course, this simplified example could be done without
75 the command callback. proc Cleanup {in out bytes {error {}}} {
76 global total
77 set total $bytes
78 close $in
79 close $out
80 if {[string length $error] != 0} { # error occurred during the
81 copy
82 } } set in [open $file1] set out [socket $server $port] fcopy $in
83 $out -command [list Cleanup $in $out] vwait total
84 The second example copies in chunks and tests for end of file in the
87 command callback proc CopyMore {in out chunk bytes {error {}}} {
88 global total done
89 incr total $bytes
90 if {([string length $error] != 0) || [eof $in] { set done
91 $total close $in close $out
92 } else { fcopy $in $out -command [list CopyMore $in $out
93 $chunk] \ -size $chunk
94 } } set in [open $file1] set out [socket $server $port] set chunk
95 1024 set total 0 fcopy $in $out -command [list CopyMore $in $out
96 $chunk] -size $chunk vwait done
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101 eof(n), fblocked(n), fconfigure(n)
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105 blocking, channel, end of line, end of file, nonblocking, read, trans‐
106 lation
107Tcl 8.0 fcopy(n)