Table of Contents

• Compiled vs. Interpreted
• Shebang
• Config Files
• Environment Variables
• PATH Variable
• Modifying PATH

---

Compiled vs. Interpreted

• sh is a compiled binary, often written in C.
• .sh is a shell script — a plain text file interpreted by a shell like sh, bash, or zsh.
• Compiled executables can run directly. Scripts require an interpreter.

---

Shebang

• A shebang (#!) tells the shell which program to use to run the script.
• Syntax:

#! interpreter [optional-arg]

Examples:

#!/bin/bash       # Bash
#!/usr/bin/zsh    # Zsh
#!/usr/bin/python3  # Python 3

• Without a shebang, scripts need to be run like: bash script.sh

---

Config Files

• Used to configure the shell at startup:

  • Bash: ~/.bashrc
  • Zsh: ~/.zshrc

These files can set:

• Environment variables
• Aliases
• PATH modifications

---

Environment Variables

• Available to all child processes of the shell.
• View current variables:

env

• Set a variable:

export NAME="Adarsh"
echo $NAME

• Scripts can access exported variables:

introduce.sh:

#!/bin/sh
echo "Hi I'm $NAME"

Make it executable:

chmod +x introduce.sh
./introduce.sh  # Hi I'm Adarsh

---

PATH Variable

• A colon-separated list of directories the shell checks to find commands.

echo $PATH

Example:

/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin

• Without PATH, you’d have to run /bin/ls instead of just ls.

---

Modifying PATH

• Append a new directory to your current PATH:

export PATH="$PATH:/your/custom/path"

• Add this to ~/.bashrc or ~/.zshrc to make it persistent across sessions.