设置从命名管道读取的管道而不会在 bash 中阻塞
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Setting up pipelines reading from named pipes without blocking in bash
提问by Charles Duffy
I'm looking to call a subprocess with a file descriptor opened to a given pipe such that the open() call does not hang waiting for the other side of the pipe to receive a connection.
我正在寻找一个子进程，它的文件描述符打开给给定的管道，这样 open() 调用就不会挂起，等待管道的另一端接收连接。
To demonstrate:
展示：
$ mkfifo /tmp/foobar.pipe
$ some_program --command-fd=5 5</tmp/foobar.pipe
In this case, some_programis not run until some process has /tmp/foobar.pipeopen for write; however, some_programhas useful effects even when it isn't receiving commands, so desired behavior is for some_programto be immediately executed.
在这种情况下，some_program直到某个进程/tmp/foobar.pipe打开写入时才运行；然而，some_program即使在它没有接收命令时也有有用的效果，因此需要some_program立即执行所需的行为。
Mechanisms to do this by exec'ing through an alternate scripting language (python, perl, etc) or a C wrapper which open /tmp/foobar.pipewith the O_NONBLOCKflag are obvious; I'm looking for a pure-bash solution, should one be possible.
通过替代脚本语言（python、perl 等）或/tmp/foobar.pipe用O_NONBLOCK标志打开的 C 包装器来执行此操作的机制是显而易见的；我正在寻找一种纯 bash 解决方案，如果可能的话。
回答by Charles Duffy
Opening the FD read/write rather than read-only when setting up the pipeline prevents blocking.
在设置管道时打开 FD 读/写而不是只读可以防止阻塞。
To be a bit more specific:
更具体一点：
$ mkfifo /tmp/foobar.pipe
$ some_program --command-fd=5 5<>/tmp/foobar.pipe
prevents the undesired blocking behavior, as 5<>/tmp/foobar.pipeopens in RW mode (as opposed to opening in read-only mode as with 5</tmp/foobar.pipe) although O_NONBLOCKis still set. Thanks to waldner on irc://irc.freenode.org/#bash for this pointer.
防止不希望的阻塞行为，因为5<>/tmp/foobar.pipe在 RW 模式下打开（而不是在只读模式下打开5</tmp/foobar.pipe），尽管O_NONBLOCK仍然设置。感谢 irc://irc.freenode.org/#bash 上的 waldner 提供了这个指针。
回答by Sec
The only way I know getting this kind of result is a hack:
我知道获得这种结果的唯一方法是 hack：
mkfifo /tmp/foobar.in
mkfifo /tmp/foobar.out
( cat </tmp/foobar.in ) >/tmp/foobar.out &
some_program --command-fd=5 5</tmp/foobar.out
perhaps this helps :-)
也许这有帮助:-)
