是否检测stdout是否重定向到管道(而不是文件，字符设备，终端或套接字)? [英] Detect if stdout is redirected to a pipe (not to a file, character device, terminal, or socket)?
问题描述
理想情况下，这可以在shell中编写脚本，但是Perl或Python可以. C代码可能会有所帮助，但可能会降低成本/收益.
Ideally, this would be scriptable in shell, but Perl or Python would be fine. C code could be helpful, but probably fails cost/benefit.
我认识到重定向到FIFO(命名管道)可能与真实管道没有区别， 这足以说明我根本不在乎的情况.
I recognize that redirection to a FIFO (named pipe) may be indistinguishable from a real pipe, and that is enough of an edge case that I don't really care.
严格的POSIX解决方案是最好的，而与UNIX/Linux无关的方案是最好的，但是我现在至少需要在Darwin(MacOS X)上可以使用的解决方案.
Strict POSIX solutions are best, UNIX/Linux variant-independent are next best, but at least something that works on Darwin (MacOS X) is what I need right now.
Before you write your answer - I already know about test -t - that will tell me whether stdout is a terminal (in which case it is definitely not a pipe - but it will not tell me whether stdout has been redirected to a file, non-terminal character device, or UNIX-domain socket rather than a pipe.
预期的用例:我有一个命令应在外壳的反引号内运行，
这样它就可以输出设置环境变量的命令.
如果标准输出未重定向到管道，我希望该命令以错误中止，
那样的话，它肯定不会被eval `mycommand`;调用.
Intended use case: I have a command that should be run within backquotes in the shell,
so that it can output commands that set environment variables.
I would like the command to abort with an error if stdout is not redirected to a pipe,
as in that case it definitely wasn't invoked by eval `mycommand`;.
如果在反引号内运行命令时，shell会设置一些特殊的环境变量会有所帮助，但是由于它可能特定于bash或zsh或某些东西，因此管道检测更为重要.
If there's some special environment variable that a shell will set when running a command within backquotes that would be helpful, but as it is likely to be specific to bash or zsh or something, pipe-detection is more important.
推荐答案
(我的评论根据Alex Dupuy的建议进行了回答)
既然您说过可以使用perl，我想您可以使用它的-p文件测试运算符( perldoc. perl.org/functions/-X.html )；像perl -e 'exit(-p STDOUT ? 0 : 1);'这样的东西会告诉您stdout是管道还是fifo(没有区分它们).
(my comment turned to answer per Alex Dupuy's suggestion)
Since you said you can use perl, I guess you can use its -p file test operator (perldoc.perl.org/functions/-X.html); something like perl -e 'exit(-p STDOUT ? 0 : 1);' will tell you if stdout if a pipe or a fifo (without distinguishing between them).
首先，从shell调用它正是我使用perl -e的原因:)
Fwiw, calling that from the shell is exactly the reason why I used perl -e :)
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