在Bash中的命令不适用于管道中的第二个命令之前设置环境变量 [英] Setting an environment variable before a command in Bash is not working for the second command in a pipe

问题描述

在给定的外壳中，通常我会设置一个或多个变量，然后运行命令.最近，我了解了在命令前添加变量定义的概念:

In a given shell, normally I'd set a variable or variables and then run a command. Recently I learned about the concept of prepending a variable definition to a command:

FOO=bar somecommand someargs

这可行...有点.当您更改LC_ *变量(这似乎会影响命令，但不它的参数，例如'[az]'char范围)时，或者在将输出管道输送到因此，另一个命令:

This works... kind of. It doesn't work when you're changing a LC_* variable (which seems to affect the command, but not its arguments, for example, '[a-z]' char ranges) or when piping output to another command thusly:

FOO=bar somecommand someargs | somecommand2  # somecommand2 is unaware of FOO

我也可以在somecommand2前面加上"FOO = bar"，它可以工作，但是会增加不必要的重复，并且对根据变量解释的参数没有帮助(例如'[az]')

I can prepend somecommand2 with "FOO=bar" as well, which works, but which adds unwanted duplication, and it doesn't help with arguments that are interpreted depending on the variable (for example, '[a-z]').

那么，单行执行此操作的好方法是什么?

So, what's a good way to do this on a single line?

我在考虑以下问题:

FOO=bar (somecommand someargs | somecommand2)  # Doesn't actually work

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我有很多好的答案！目标是保持这种单线，最好不使用导出".总体上，使用Bash调用的方法是最好的，尽管括号中带有"export"的版本更为紧凑.使用重定向而不是管道的方法也很有趣.

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I got lots of good answers! The goal is to keep this a one-liner, preferably without using "export". The method using a call to Bash was best overall, though the parenthetical version with "export" in it was a little more compact. The method of using redirection rather than a pipe is interesting as well.

推荐答案

FOO=bar bash -c 'somecommand someargs | somecommand2'

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