How Shell Scripts Work

1. Interpreter: A shell script is interpreted rather than compiled. The script runs line-by-line, where each command is executed by the shell (like Bash, Zsh, etc.).
2. Shebang: The first line in a shell script usually starts with a special sequence called the shebang (#!). It specifies the interpreter to be used to execute the script.
   
   #!/bin/bash
   
   This example tells the system to use the Bash shell to execute the script.
3. Writing Commands: After the shebang, you can write any series of shell commands. Each command is written on a new line, and the shell executes them in the order they appear.
4. Variables: You can define and use variables within a script.
   
   #!/bin/bash
NAME="John"
echo "Hello, $NAME"
   
5. Control Structures: You can include loops, conditionals, and functions, making shell scripts quite powerful.
   
   #!/bin/bash
if [ "$1" -gt 10 ]; then
echo "Number is greater than 10"
else
echo "Number is less than or equal to 10"
fi
   
6. Execution: Before running the script, you may need to set its permissions to be executable:
   
   chmod +x script.sh
   
   Then, you can run the script:
   
   ./script.sh

Example Shell Script:

Here’s an example of a simple shell script:

#!/bin/bash
# A simple greeting script
echo "Enter your name:"
read NAME
echo "Hello, $NAME! Welcome!"

Common Shells:

• Bash (Bourne Again Shell) is the most common shell in Linux systems.
• Zsh, Sh, Fish are other types of shells you might encounter.