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 and character translations configured for the
59 channels. This means that the incoming characters are converted inter‐
60 nally first UTF-8 and then into the encoding of the channel fcopy
61 writes to. See the manual entry for fconfigure for details on the
62 -encoding and -translation options. No conversion is done if both chan‐
63 nels are set to encoding “binary” and have matching translations. If
64 only the output channel is set to encoding “binary” the system will
65 write the internal UTF-8 representation of the incoming characters. If
66 only the input channel is set to encoding “binary” the system will
67 assume that the incoming bytes are valid UTF-8 characters and convert
68 them according to the output encoding. The behaviour of the system for
69 bytes which are not valid UTF-8 characters is undefined in this case.
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73 The first example transfers the contents of one channel exactly to
74 another. Note that when copying one file to another, it is better to
75 use file copy which also copies file metadata (e.g. the file access
76 permissions) where possible.
77 fconfigure $in -translation binary
78 fconfigure $out -translation binary
79 fcopy $in $out
80 This second example shows how the callback gets passed the number of
82 bytes transferred. It also uses vwait to put the application into the
83 event loop. Of course, this simplified example could be done without
84 the command callback.
85 proc Cleanup {in out bytes {error {}}} {
86 global total
87 set total $bytes
88 close $in
89 close $out
90 if {[string length $error] != 0} {
91 # error occurred during the copy
92 }
93 }
94 set in [open $file1]
95 set out [socket $server $port]
96 fcopy $in $out -command [list Cleanup $in $out]
97 vwait total
98 The third example copies in chunks and tests for end of file in the
100 command callback
101 proc CopyMore {in out chunk bytes {error {}}} {
102 global total done
103 incr total $bytes
104 if {([string length $error] != 0) || [eof $in]} {
105 set done $total
106 close $in
107 close $out
108 } else {
109 fcopy $in $out -size $chunk \
110 -command [list CopyMore $in $out $chunk]
111 }
112 }
113 set in [open $file1]
114 set out [socket $server $port]
115 set chunk 1024
116 set total 0
117 fcopy $in $out -size $chunk \
118 -command [list CopyMore $in $out $chunk]
119 vwait done
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123 eof(n), fblocked(n), fconfigure(n), file(n)
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127 blocking, channel, end of line, end of file, nonblocking, read, trans‐
128 lation
129Tcl 8.0 fcopy(n)