環(huán)境變量與shell變量的區(qū)別在於作用域和可用性。 1. shell變量僅在當(dāng)前shell會(huì)話中有效，不會(huì)傳遞給子進(jìn)程或外部程序，適用於臨時(shí)存儲(chǔ)或腳本內(nèi)部邏輯；2. 環(huán)境變量是已導(dǎo)出的shell變量，可在當(dāng)前shell及其所有子進(jìn)程中訪問，用於配置應(yīng)用程序行為。若不確定使用哪種變量，可問自己“該值是否需要在當(dāng)前shell之外可見”，是則用環(huán)境變量，否則用shell變量。兩者在外觀和操作上相似，但關(guān)鍵區(qū)別在於可見性和作用範(fàn)圍，理解這一點(diǎn)對(duì)調(diào)試腳本和配置工具至關(guān)重要。

The difference between an environment variable and a shell variable comes down to scope and availability. In short: environment variables are available system-wide (to the process and any child processes), while shell variables are local to the current shell session only .

What is a shell variable?

A shell variable is created and used within a specific shell session. It's useful for temporary storage or scripting purposes, but it doesn't get passed to other programs or subprocesses you might launch from that shell.

For example:

 MY_VAR="hello"
echo $MY_VAR

This creates a shell variable MY_VAR and then prints it. But if you try to access MY_VAR from a script or program launched from this shell, it won't be visible unless you explicitly export it.

Key points:

• Only accessible in the current shell.
• Not inherited by child processes.
• Useful for internal shell scripting logic.

What is an environment variable?

An environment variable is like a shell variable that has been exported so it's available not just in the shell, but also to any program or subprocess started from that shell.

To turn the earlier shell variable into an environment variable:

 export MY_VAR="hello"

Now, any command or script you run from this shell can access MY_VAR .

Key points:

• Available to the shell and all its child processes.
• Used to configure behavior of applications and tools.
• Can be set temporarily in the shell or permanently in config files like .bashrc , .zshrc , etc.

How do they appear and interact?

You can see environment variables using:

 printenv

Or check both environment and shell variables with:

 set

In practice, some variables start as shell variables and become environment variables when exported. Others are already set as environment variables by your login shell or system configuration.

Common environment variables include:

• PATH – where the system looks for executable commands.
• HOME – the current user's home directory.
• USER – the current username.

Shell-only variables might include things like loop counters in scripts or temporary values that don't need to be shared.

When should you use each?

Use shell variables when:

• You're writing a script and need a temporary value.
• The value doesn't need to be seen by external commands.
• You're working interactively and just want to store something quickly.

Use environment variables when:

• You want a subprocess or program to have access to the value.
• You're configuring application behavior (like API keys or debug flags).
• You're setting up global settings that affect multiple tools or sessions.

If you're unsure, ask yourself: “Does this value need to be visible outside of my current shell context?” If yes → export it. If no → keep it local.

基本上就這些。 They're similar in how they look and work, but the key difference lies in visibility and scope — and knowing which one you're using matters when debugging scripts or configuring tools.

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