Shell腳本處理命令行參數(shù)可通過位置訪問、選項(xiàng)解析和默認(rèn)值實(shí)現(xiàn)。首先，使用$1、$2等獲取位置參數(shù)，${10}處理超過9個(gè)參數(shù)，"$@"保留空格；其次，通過getopts處理帶參數(shù)的選項(xiàng)如-f、-l，並用case匹配及OPTARG捕獲值；最後，提供默認(rèn)值如name=${1:-"Guest"}或手動(dòng)解析鍵值對(duì)如--name=John，同時(shí)注意引用、shift控制及錯(cuò)誤處理以確保靈活性與安全性。

When you're writing a shell script, handling command-line arguments is one of the basic but essential skills. It lets your script behave differently based on what the user provides when running it — like filenames, options, or values.

Accessing Arguments by Position

In a shell script, arguments are accessed using positional parameters. $1 refers to the first argument, $2 the second, and so on. If you need all arguments at once, use $@ or $* .

For example:

 #!/bin/bash
echo "First argument: $1"
echo "Second argument: $2"

If you run this script like:

 ./script.sh hello world

You'll get:

 First argument: hello
Second argument: world

Keep in mind:

• If there are more than 9 arguments, you have to enclose the number in braces: ${10}
• Quoting $@ (like "$@" ) preserves spaces in arguments, which is safer than using $*

Handling Options with getopts

If your script supports flags or options (like -f for filename or -v for verbose), getopts is the built-in tool to use.

Here's how you might handle -f and -l :

 while getopts f:l: option; do
  case $option in
    f) fname=$OPTARG;;
    l) lname=$OPTARG;;
  esac
done

Then call it like:

 ./script.sh -f John -l Doe

Some notes:

• The colon after f:l: means those options require an argument
• Always test that required options are provided
• You can add a ? case in the case block to catch invalid options

Dealing with Optional and Default Values

Not every argument needs to be mandatory. Sometimes it makes sense to provide defaults if the user didn't specify.

For instance:

 name=${1:-"Guest"}
echo "Hello, $name"

This will print "Hello, Guest" if no argument is given, or use whatever name the user passes.

Another way is using a check:

 if [ -z "$1" ]; then
  echo "No name provided, defaulting to Guest"
  name="Guest"
else
  name="$1"
fi

This gives you more flexibility if you want to log or warn the user when a default kicks in.

Advanced: Using Named Arguments (Key-Value Style)

Sometimes scripts grow beyond simple flags and need full key-value pairs, like --name=John or --verbose=true . While getopts doesn't support long options well, you can parse them manually:

 for arg in "$@"
do
  case $arg in
    --name=*)
      NAME="${arg#*=}"
      shift
      ;;
    --verbose=*)
      VERBOSE="${arg#*=}"
      shift
      ;;
  esac
done

This approach gives you more flexibility but requires careful parsing and validation.

A few things to keep in mind:

• Use shift carefully to avoid infinite loops
• Quote everything to prevent issues with spaces
• Consider adding error handling for unsupported keys

That's pretty much how you work with command-line arguments in shell scripts. There are different ways depending on complexity, but sticking to basics usually keeps your scripts clean and maintainable.

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