在 Bash 中檢查命令是否成功可通過(guò)退出狀態(tài)碼實(shí)現(xiàn)。0 表示成功，非零值表示錯(cuò)誤；使用 $? 可查看上一命令的退出碼，如 ls /some/directory; echo $?；也可直接在 if 語(yǔ)句中判斷，如 if mycommand --option; then echo "Success"; else echo "Failed"; fi；常見(jiàn)退出碼包括 0（成功）、1（一般錯(cuò)誤）、2（命令用法錯(cuò)誤）等；使用 set -e 可使腳本在任一命令失敗時(shí)立即退出，但需謹(jǐn)慎使用以避免誤判非嚴(yán)重錯(cuò)誤。

In Bash, checking whether a command succeeded is straightforward: you look at its exit status. By default, a command returns 0 if it succeeded and a non-zero value (usually 1, but sometimes others) if something went wrong.

Here’s how to check it in your scripts or on the command line.

Using $? to check the exit code

After running any command in Bash, you can immediately check the special variable $?. It holds the exit status of the last command executed.

For example:

ls /some/directory
echo $?

• If ls found the directory and listed it, you’ll see 0.
• If the directory doesn’t exist or there was a permission issue, you’ll get a number like 2.

This method works well in scripts when you want to conditionally do something based on success or failure.

A simple usage in a script:

#!/bin/bash

mycommand --option
if [ $? -eq 0 ]; then
  echo "Command succeeded"
else
  echo "Command failed"
fi

Just remember — once another command runs after the one you care about, $? gets overwritten. So use it right away.

Using if directly with the command

Instead of using $?, you can put the command directly inside an if statement. This is cleaner and avoids possible mistakes from forgetting that $? changes quickly.

Here’s how that looks:

if mycommand --option; then
  echo "Success!"
else
  echo "Failed!"
fi

This is often preferred because:

• It's more readable.
• You don't have to manually compare numbers.
• Less chance of accidentally using the wrong $?.

You can also chain this with other logic, like retrying a command or logging errors.

Common exit codes and what they mean

Exit codes are defined by each command, but some are standard:

• 0 = Success
• 1 = General error
• 2 = Misuse of shell builtins (like incorrect options)
• 126 = Command found but not executable
• 127 = Command not found
• 130 = Script interrupted (e.g., Ctrl C pressed)

These aren’t always consistent across all programs, but they give a general idea of what went wrong.

If you're debugging a script or trying to understand why something didn’t work, checking these values can help pinpoint the issue.

Use set -e to exit on error in scripts

If you’re writing a script and want it to stop as soon as any command fails, add this at the top:

#!/bin/bash
set -e

This tells Bash to exit immediately if any command exits with a non-zero status. It’s useful for automation where partial execution might leave things in an inconsistent state.

But be careful — sometimes commands return non-zero even when it’s not a serious problem. For example, grep returns 1 if it finds no matches, which isn’t always an error.

So, use set -e wisely, especially if you're relying on certain commands to run even if previous ones fail.

That’s basically it. Checking if a command succeeded in Bash comes down to understanding exit codes and knowing how to access or act on them — either through $?, direct conditionals, or script flags like set -e.

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