我有一个变量，比方说xx，带有索引0和索引1值的列表。我想修改一个先前定义了函数pptable的脚本（不是我的），即
proc pptable {l1 l2} {
foreach i1 $l1 i2 $l2 {
puts " [format %6.2f $i1]\t[format %6.2f $i2]"
}
}
这样它就可以使用输出显示两列
pptable [lindex $xx 1] [lindex $xx 0]
但是，我想将输出直接写入文件。你能告诉我如何将数据发送到文件而不是显示器吗？
这样做的最好方法之一是stack在channel transform上将stdout重定向到你想要去的地方。即使对stdout的写入发生在C代码或不同的线程中，因为它插入到通道机制中也是如此。代码有点长（并且需要Tcl 8.6）但是可靠且实际上非常简单。
package require Tcl 8.6; # *REQUIRED* for [chan push] and [chan pop]
proc RedirectorCallback {targetHandle op args} {
# The switch/lassign pattern is simplest way of doing this in one procedure
switch $op {
initialize {
lassign $args handle mode
# Sanity check
if {$mode ne "write"} {
close $targetHandle
error "this is just a write transform"
}
# List of supported subcommands
return {initialize finalize write}
}
finalize {
lassign $args handle
# All we need to do here is close the target file handle
close $targetHandle
}
write {
lassign $args handle buffer
# Write the data to *real* destination; this does the redirect
puts -nonewline $targetHandle $buffer
# Stop the data going to *true* stdout by returning empty string
return ""
# If we returned the data instead, this would do a 'tee'
}
default {
error "unsupported subcommand"
}
}
}
# Here's a wrapper to make the transform easy to use
proc redirectStdout {file script} {
# Stack the transform onto stdout with the file handle to write to
# (which is going to be $targetHandle in [redirector])
chan push stdout [list RedirectorCallback [open $file "wb"]]
# Run the script and *definitely* pop the transform after it finishes
try {
uplevel 1 $script
} finally {
chan pop stdout
}
}
我们如何实际使用它？这在实践中非常容易：
# Exactly the code you started with
proc pptable {l1 l2} {
foreach i1 $l1 i2 $l2 {
puts " [format %6.2f $i1]\t[format %6.2f $i2]"
}
}
# Demonstrate that stdout is working as normal
puts "before"
# Our wrapped call that we're capturing the output from; pick your own filename!
redirectStdout "foo.txt" {
pptable {1.2 1.3 1.4} {6.9 6.8 6.7}
}
# Demonstrate that stdout is working as normal again
puts "after"
当我运行该代码时，我得到了这个：
bash$ tclsh8.6 stdout-redirect-example.tcl before after bash$ cat foo.txt 1.20 6.90 1.30 6.80 1.40 6.70
我相信这正是你要找的。
如果你使用Tcllib和TclOO帮助处理机器，你可以用更少的代码完成这个：
package require Tcl 8.6
package require tcl::transform::core
oo::class create WriteRedirector {
superclass tcl::transform::core
variable targetHandle
constructor {targetFile} {
set targetHandle [open $targetFile "wb"]
}
destructor {
close $targetHandle
}
method write {handle buffer} {
puts -nonewline $targetHandle $buffer
return ""
}
# This is the wrapper, as a class method
self method redirectDuring {channel targetFile script} {
chan push $channel [my new $targetFile]
try {
uplevel 1 $script
} finally {
chan pop $channel
}
}
}
用法示例：
proc pptable {l1 l2} {
foreach i1 $l1 i2 $l2 {
puts " [format %6.2f $i1]\t[format %6.2f $i2]"
}
}
puts "before"
WriteRedirector redirectDuring stdout "foo.txt" {
pptable {1.2 1.3 1.4 1.5} {6.9 6.8 6.7 6.6}
}
puts "after"
我假设你不想或不能修改现有的脚本和proc pptable，对吗？
如果是这样，根据您的具体情况，有不同的选择：
stdout：tclsh yourscript.tcl > your.outputs（明确定义的范围）：
rename ::puts ::puts.orig
proc puts args {
set fh [open your.out w];
::puts.orig $fh $args;
close $fh
}
# run pptable, source the script
之前已经讨论过这个主题，例如tcl stop all output going to stdout channel?stdout频道（不一定推荐）：
close stdout
open your.out w
# run pptable, source the script
这也在之前已经详细阐述过，例如： Tracing stdout and stderr in Tcl