Note: I’m not an expert. I’m writing this blog just to document my learning journey. 🚀
🧠 What is a Shell Script?
A shell script is a text file containing a sequence of shell commands that are executed one after another, as if you were typing them into a terminal.
It uses a shell (like bash, sh, or zsh) as the program that interprets and runs the commands.
🧩 Key Concepts
🔹 1. Shell = Command-Line Interpreter
The shell is a program that takes user input and executes commands.
- Example shells:
bash,zsh,fish,dash,sh - They understand commands like
cd,ls,echo,cp, etc. - Shells can also run scripts — a file with a list of commands.
🔹 2. Shell Script = Text File of Commands
A shell script is just a plain text file with:
- A shebang (
#!) - A list of commands
- Optional logic (if, loops, functions)
#!/bin/bash
echo "Hello, world!"
- The first line (
#!/bin/bash) tells the system to use the bash shell to interpret the file. - Each line is executed top to bottom, like typing into the terminal.
🔹 3. Variables, Conditions, and Loops
Shell scripts become powerful because they support programming logic:
📦 Variables:
name="Computer"
echo "Hello, $name"
🔁 Loops:
for file in *.txt; do
echo "Processing $file"
done
❓ Conditionals:
if [ "$name" = "Computer" ]; then
echo "Welcome back!"
fi
🔹 4. Exit Codes and Errors
Every command returns an exit code:
-
0= success - non-zero = error
You can check:
if [ $? -ne 0 ]; then
echo "The last command failed!"
fi
Or use set -e to make the script stop on any error.
🔹 5. Execution
Make the script executable:
chmod +x myscript.sh
./myscript.sh
Or run it like:
bash myscript.sh
🧠 Final Definition
A shell script is a plain text file that contains a structured sequence of commands written for a shell interpreter. It allows automation of tasks by combining built-in shell functionality (variables, conditionals, loops) with standard system commands. The script is executed line-by-line, and each command’s success or failure affects the flow of execution.
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