Learn Shell Scripting: From Hello World to Practical Tools

The article is a step‑by‑step guide for beginners to learn Shell scripting on Linux. It encourages readers to bookmark and practice the examples so they can move from merely understanding scripts to writing them confidently.

Step 1: Write the simplest script

#!/bin/bash

echo "你好，Shell 脚本！"

Create a file (e.g., hello.sh ), paste the above content, save, make it executable with chmod +x hello.sh , and run it with ./hello.sh . The output will be "你好，Shell 脚本！".

Step 2: Variables are essential

#!/bin/bash

name="小白DBA"

echo "你好，$name"

Save as var.sh , give execute permission, and run. Important notes: assignment must not contain spaces ( name="value" ), double quotes allow variable expansion, while single quotes keep the literal string.

Step 3: Add conditionals

Example – check if a file exists:

#!/bin/bash

if [ -f /etc/passwd ]; then
    echo "文件存在"
else
    echo "文件不存在"
fi

-f tests for a regular file, [] is the test syntax, and then / fi delimit the block. Another example shows reading user input and comparing it to "root".

Step 4: Loops for batch operations

Ping a range of IPs:

#!/bin/bash

for ip in 192.168.1.{1..5}
do
    ping -c 1 $ip > /dev/null
    if [ $? -eq 0 ]; then
        echo "$ip 通了"
    else
        echo "$ip 不通"
    fi

done

Key points: for ... in syntax, {1..5} expands to 1‑5, $? is the previous command’s exit status, and > /dev/null suppresses ping output.

Step 5: Functions for modularity

#!/bin/bash

check_port() {
    if ss -tunlp | grep ":$1" > /dev/null; then
        echo "端口 $1 正在监听"
    else
        echo "端口 $1 未打开"
    fi
}

check_port 22
check_port 80

The check_port function receives a port number as $1 and reports whether it is being listened on.

Step 6: Real‑world case – service status checker

#!/bin/bash

SERVICES=("sshd" "mysqld" "nginx")

for svc in "${SERVICES[@]}"
do
    systemctl is-active --quiet $svc
    if [ $? -eq 0 ]; then
        echo "$svc 运行中"
    else
        echo "$svc 没有运行"
    fi
done

This script iterates over an array of service names, uses systemctl is-active --quiet to test each, and prints whether it is running.

Step 7: User interaction and arguments

#!/bin/bash

if [ $# -lt 1 ]; then
    echo "用法：$0 <文件路径>"
    exit 1
fi

file=$1

if [ -f "$file" ]; then
    echo "$file 是一个文件"
else
    echo "$file 不存在"
fi

Explanation of special variables: $# (argument count), $0 (script name), $1 (first argument), and exit 1 to terminate with an error.

Step 8: Debugging tricks

Run a script with tracing:

bash -x myscript.sh

Or insert set -x at the start of a script and set +x to stop tracing.

What to learn next?

Try writing your own small scripts, such as batch backing up files, scheduled log cleanup with crontab , disk‑usage monitoring with alerts, or an interactive menu‑driven script.

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