Linux shell 如何避免重复加载环境变量？

Question

使用 zsh，每次 source 或者打开子 shell 的时候都会重复加载环境变量

原本的环境变量：👇

─➤  echo -e ${PATH//:/\\n}
/home/bot/.cargo/bin
/home/bot/opt/go/bin
/home/bot/.local/bin
/home/bot/opt/pycharm/pycharm-2021.2/bin
/home/bot/opt/python3.10.1/bin
/usr/local/sbin
/usr/local/bin
/usr/sbin
/usr/bin
/sbin
/bin
/usr/games
/usr/local/games
/snap/bin

子 shell 中的环境变量👇

─➤  echo -e ${PATH//:/\\n}
/home/bot/.local/share/virtualenvs/ideaboom-3stdf9Mx/bin
/home/bot/opt/go/bin
/home/bot/.local/bin
/home/bot/opt/pycharm/pycharm-2021.2/bin
/home/bot/opt/python3.10.1/bin
/home/bot/.cargo/bin
/home/bot/opt/go/bin
/home/bot/.local/bin
/home/bot/opt/pycharm/pycharm-2021.2/bin
/home/bot/opt/python3.10.1/bin
/usr/local/sbin
/usr/local/bin
/usr/sbin
/usr/bin
/sbin
/bin
/usr/games
/usr/local/games
/snap/bin

可以看到开头这部分变量被重新加载了👇

/home/bot/opt/go/bin
/home/bot/.local/bin
/home/bot/opt/pycharm/pycharm-2021.2/bin
/home/bot/opt/python3.10.1/bin

造成重复加载环境变量的原因，我猜测是每个子 shell 都会重新跑一遍 ~/.zshenv 文件！

我的 ~/.zshenv 文件👇

export RUSTUP_DIST_SERVER=https://mirrors.ustc.edu.cn/rust-static
export RUSTUP_UPDATE_ROOT=https://mirrors.ustc.edu.cn/rust-static/rustup
export PATH=/home/bot/opt/python3.10.1/bin:$PATH
export PATH=/home/bot/opt/pycharm/pycharm-2021.2/bin:$PATH
export PATH=/home/bot/.local/bin:$PATH
export PATH=/home/bot/opt/go/bin:$PATH

. "$HOME/.cargo/env"

其中的 "$HOME/.cargo/env" 脚本有去重的功能,参考了 "$HOME/.cargo/env" 防止重复加载环境变量的做法：

#!/bin/sh
# rustup shell setup
# affix colons on either side of $PATH to simplify matching
case ":${PATH}:" in
    *:"$HOME/.cargo/bin":*)
        ;;
    *)
        # Prepending path in case a system-installed rustc needs to be overridden
        export PATH="$HOME/.cargo/bin:$PATH"
        ;;
esac

但是这个脚本的 shell 语法让我看不懂，有什么简单的办法可以封装一下就能防止在子 shell 中重复加载环境变量吗？

越简单优雅越好！😊😊😊

Answer 1

楼上的方法也是不恰当的，因为它要么存在一个就全部不再加，要么一次性全部加上，其实正确的脚本应该是

#!/bin/sh
# rustup shell setup
# 下面分别对每个路径进行测试，判断是否需要增加到PATH环境变量中去。
case ":${PATH}:" in
    *:"${HOME}/opt/go/bin":*)
        ;;
    *)
        export PATH=${HOME}/opt/go/bin:${PATH}
        ;;
esac

case ":${PATH}:" in
    *:"${HOME}/.local/bin":*)
        ;;  
    *)
        export PATH=${HOME}/.local/bin:${PATH}  
        ;;
esac
   
case ":${PATH}:" in
    *:"${HOME}/opt/pycharm/pycharm-2021.2/bin":*)
        ;;    
    *)
        export PATH=${HOME}/opt/pycharm/pycharm-2021.2/bin:${PATH} 
        ;;
esac    

case ":${PATH}:" in
    *:"${HOME}/opt/python3.10.1/bin":*)
        ;;
    *)
        export PATH=${HOME}/opt/python3.10.1/bin:${PATH} 
        ;;
esac

另外一种写法可能更简洁，总之一个原则是判断PATH中是否包含待加入的路径:

#!/bin/sh
# 下面分别对每个路径进行测试，判断是否需要增加到PATH环境变量中去。
if [[ ":${PATH}:" != *":${HOME}/opt/go/bin:"* ]]; then
    export PATH=${HOME}/opt/go/bin:${PATH}
fi

if [[ ":${PATH}:" != *":${HOME}/.local/bin:"* ]]; then
    export PATH=${HOME}/.local/bin:${PATH}
fi

if [[ ":${PATH}:" != *":${HOME}/opt/pycharm/pycharm-2021.2/bin:"* ]]; then
    export PATH=${HOME}/opt/pycharm/pycharm-2021.2/bin:${PATH}
fi

if [[ ":${PATH}:" != *":${HOME}/opt/python3.10.1/bin:"* ]]; then
    export PATH=${HOME}/opt/python3.10.1/bin:${PATH}
fi

这里的关键是用*通配符展开字符串进行比较，判断包含关系，而加的:是因为PATH环境变量是以它分隔各个搜索路径，这样添加了可以保证完整匹配路径。

Answer 2

#!/bin/sh
# rustup shell setup
# affix colons on either side of $PATH to simplify matching
case ":${PATH}:" in
    *:"$HOME/opt/go/bin":*)
        ;;
    ":${PATH}:" in
    *:"$HOME/.local/bin":*)
        ;;    
    
    ":${PATH}:" in
    *:"$HOME/opt/pycharm/pycharm-2021.2/bin":*)
        ;;    
    
    ":${PATH}:" in
    *:"$HOME/opt/python3.10.1/bin":*)
        ;;
    
    *)
        # Prepending path in case a system-installed rustc needs to be overridden
        export PATH=/home/bot/opt/python3.10.1/bin:$PATH
        export PATH=/home/bot/opt/pycharm/pycharm-2021.2/bin:$PATH
        export PATH=/home/bot/.local/bin:$PATH
        export PATH=/home/bot/opt/go/bin:$PATH
        ;;
esac

在"$HOME/.myenv/"路径下保存上面的脚本为env，添加可执行权限，修改~/.zshenv 文件：

export RUSTUP_DIST_SERVER=https://mirrors.ustc.edu.cn/rust-static
export RUSTUP_UPDATE_ROOT=https://mirrors.ustc.edu.cn/rust-static/rustup
. "$HOME/.myenv/env"
. "$HOME/.cargo/env"