在Shell腳本中，特殊變量$#、$*和@用於處理命令行參數(shù)，其行為各不相同。 1. $#表示傳遞給腳本的參數(shù)個(gè)數(shù)，適用於檢查參數(shù)數(shù)量是否正確；2. $*將所有參數(shù)視為一個(gè)整體字符串，默認(rèn)以空格連接，適合日誌記錄或整體傳遞參數(shù)，但可能無法保留原始空格或引號(hào)；3. $@將每個(gè)參數(shù)作為獨(dú)立字符串處理，保留原始分隔，適合遍歷參數(shù)或傳遞帶空格的參數(shù)如文件名。使用時(shí)應(yīng)始終用引號(hào)包裹這些變量以避免特殊字符引發(fā)問題。

When working with shell scripts, especially in Bash, you'll often see special variables like $* , $@ , and $# . These variables are used to access command-line arguments passed to a script, but they behave differently depending on how you use them. Here's a breakdown of what each one does and when to use it.

$# – Count the Number of Arguments

This is the simplest one: $# gives you the number of arguments passed to the script.

For example:

 #!/bin/bash
echo "You provided $# arguments"

If you run this script like so:

 ./script.sh apple banana cherry

It will output:

 You provided 3 arguments

Use $# when you need to check if the user provided the correct number of inputs or handle cases where the argument count affects logic flow.

$* – All Arguments as One String

$* treats all the positional arguments as a single string, joined together with spaces (or the first character of IFS , which defaults to space).

Example:

 #!/bin/bash
echo "All arguments: $*"

Running:

 ./script.sh one two three

Will print:

 All arguments: one two three

This can be useful if you just want to log or pass all arguments as a single unit, but be careful — it may not preserve spacing or quoting properly in some contexts.

$@ – All Arguments as Separate Strings

$@ behaves similarly to $* , but with an important difference: it preserves the separation between arguments. Each argument is treated as its own string.

Example:

 #!/bin/bash
for arg in "$@"
do
  echo "Argument: $arg"
done

Running:

 ./script.sh "hello there" goodbye

Will result in:

 Argument: hello there
Argument: goodbye

Whereas if you replace "$@" with "$*" in that loop, it would treat "hello there goodbye" as one argument.

So if you're looping through arguments or passing them to another command while preserving their original structure, always use "$@" .

Here's a quick summary:

• Use $# when you need to know how many arguments were given.
• Use $* when you want to treat all arguments as a single string (less common).
• Use $@ when you want to handle each argument individually , especially when dealing with filenames or phrases that contain spaces.

And remember: always quote these variables unless you have a specific reason not to — otherwise, spaces and special characters can cause unexpected behavior.

基本上就這些。

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