不支持流程替换<(...)吗? [英] Doesn't sh support process substitution <(...)?

问题描述

在Centos 6机器上，此方法有效:

On a Centos 6 machine, this works:

bash -c 'if grep -qP --line-buffered ".+" <(tail -n 1000 -F catalina.out) ; then echo "yes"; fi'

这不是:

sh -c 'if grep -qP --line-buffered ".+" <(tail -n 1000 -F catalina.out) ; then echo "yes"; fi'

我得到:

sh: -c: line 0: syntax error near unexpected token `('
sh: -c: line 0: `if grep -qP --line-buffered ".+" <(tail -n 1000 -F catalina.out) ; then echo "yes"; fi'

不要紧记grep和尾巴.问题出在进程替换上:<(...)

Nevermind the grep and tail. The problem is with the process substitution thingy: <(...)

有人可以告诉我sh在这里有什么不同吗?

Can someone tell me what sh does differently here?

感谢您的回答！

在使用 capistrano 进行部署时出现了问题.它默认使用 sh ，但是我现在将其更改为 bash . 我无法进行常规配管的原因是，使用tail -F | grep -q --line-buffered时，grep不会在匹配后立即退出.必须像echo "" >> catalina.out这样的文件再进行一次编辑，在我的情况下这是不可接受的.

The problem arose while using capistrano for deployments. It defaults to using sh but I changed that to bash now. The reason I couldn't do the normal piping is that when using tail -F | grep -q --line-buffered, grep won't exit immediately after a match. There has to be one more edit to the file like echo "" >> catalina.out and this was not acceptable in my situation.

推荐答案

BASH仅支持语法<(...).

The syntax <(...) is only supported by BASH.

对于任何POSIX shell，请使用以下方法:

For any POSIX shell, use this approach:

sh -c 'tail -n 1000 -F catalina.out | if grep -qP --line-buffered ".+" ; then ...'

即用管道将stdin重定向移到if的前面. if会将标准输入传递到grep.

i.e. move the stdin redirection in front of the if with a pipe. The if will pass stdin on to the grep.

if tail ...| grep不起作用，因为if不能看到它是then/fi，因为管道将进程分开.

if tail ...| grep won't work since the if won't be able to see it's then/fi because the pipe separates processes.

这篇关于不支持流程替换<(...)吗?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！