Linux Command Line Mastery · 课时

变量、输入与输出

学习在 Shell 脚本中声明变量、接收用户输入并管理脚本输出。

变量、输入与输出 是 CoddyKit 上的免费 Linux Command Line Mastery 课时。这是第 1 节课，共 4 节。你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。这是 Linux Command Line Mastery 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Linux Command Line Mastery 课程共包含 4 节课。

本课时的部分内容尚未翻译，以英文显示。

What are Script Variables?

In shell scripting, variables are like containers for storing data. They help make your scripts flexible and reusable.

Instead of hardcoding values, you can use variables to hold information such as filenames, user inputs, or temporary results.

Declaring & Assigning Variables

To create a variable, you simply assign a value to a name. No special keyword is needed!

Use NAME="Coddy" (no spaces around =).
Values with spaces usually need quotes (single or double).
Numbers don't strictly need quotes, but it's often good practice for consistency.

Accessing Variable Values

To use the value stored in a variable, you prepend its name with a $ sign.

For example, if you declared GREETING="Hello", you'd use $GREETING to get "Hello". You can also use ${VARIABLE}, which is clearer in complex situations.

Variable Naming Tips

Follow these simple rules for variable names:

Start with a letter or underscore.
Can contain letters, numbers, and underscores.
Avoid using special shell keywords.
Common practice: use uppercase for global/environment variables, lowercase for script-local ones.

Demo: Using Variables

Let's see a simple script that declares and uses a variable.

Notice how $MESSAGE retrieves the stored text.

#!/bin/bash

# Declare a variable
MY_NAME="Coddy"
GREETING="Hello"

# Access and print variables
echo "$GREETING, $MY_NAME!"

# Update the variable
MY_NAME="Learner"
echo "Nice to meet you, $MY_NAME!"

Getting User Input: `read`

The read command is essential for making your scripts interactive. It waits for the user to type something and press Enter.

read VARIABLE: Stores input into VARIABLE.
read -p "Prompt: " VARIABLE: Displays a prompt before waiting for input.

Demo: Taking User Input

This script uses read -p to ask for your name and then greets you personally.

Try running it and entering your name!

#!/bin/bash

# Prompt for user's name and store it
read -p "What's your name? " USER_NAME

# Greet the user
echo "Hello, $USER_NAME! Welcome to CoddyKit."

Script Output: `echo` & `printf`

You've seen echo for basic output. It simply prints its arguments followed by a newline.

For more control, printf (like in C) allows formatted output, specifying data types and alignment. It doesn't add a newline automatically, so use \n.

Demo: Input, Output & Variables

This example combines variables, user input with read, and formatted output using printf.

It calculates a simple sum based on your input.

#!/bin/bash

# Declare a base number
BASE_NUM=10

# Get a number from the user
read -p "Enter another number: " USER_NUM

# Calculate the sum
# Use $((...)) for arithmetic operations
SUM=$((BASE_NUM + USER_NUM))

# Print the result using printf for formatting
printf "The sum of %d and %d is %d.\n" "$BASE_NUM" "$USER_NUM" "$SUM"

Quick Check

Consider the following shell script snippet:

#!/bin/bash
NAME="Alice"
read -p "Enter a city: " CITY
echo "Hello, $NAME from $CITY!"

If the user types London and presses Enter, what will be the final output?

Recap: Variables, Input, Output

Great job! You've learned the fundamentals of shell scripting:

Variables store data using VAR="value".
Access variables with $VAR or ${VAR}.
read gets user input, often with -p for a prompt.
echo prints simple messages.
printf offers formatted output.

These are building blocks for dynamic and interactive scripts!

常见问题解答

「变量、输入与输出」课时是免费的吗？

是的 — 「变量、输入与输出」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Linux Command Line Mastery 课程的其余内容，请升级到 CoddyKit PRO。 Linux Command Line Mastery 课程共包含 4 节课。

「变量、输入与输出」这节课中我会学到什么？

学习在 Shell 脚本中声明变量、接收用户输入并管理脚本输出。你通过在浏览器中直接运行的动手代码来练习 Linux Command Line Mastery，全天候 AI 导师会在你学习这节课的过程中回答你的问题。

学习 Linux Command Line Mastery 需要有经验吗？

无需任何先前经验。CoddyKit 上的 Linux Command Line Mastery 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。这是第 1 节课，共 4 节。

「变量、输入与输出」课时需要多长时间？

大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。

我能在这节 Linux Command Line Mastery 课中编写并运行代码吗？

能。每节 Linux Command Line Mastery 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。

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