在 Bash 中的命令之前设置环境变量不适用于管道中的第二个命令 [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 shell 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
这有效......有点.当您更改 LC_* 变量(这似乎影响命令，但不 其参数，例如，'[az]' 字符范围)或将输出通过管道传输到另一个命令因此:
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"，这可行，但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，在一行中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?
我正在考虑以下顺序:
FOO=bar (somecommand someargs | somecommand2) # Doesn't actually work
我得到了很多好的答案！目标是保持单行，最好不使用导出".使用 Bash 调用的方法总体上是最好的，尽管带有export"的括号版本更紧凑一些.使用重定向而不是管道的方法也很有趣.
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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