Interactive vs non interactive shell

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Two Modes of Shell Operation

1. Interactive Mode
   You type commands at a prompt and see immediate feedback.
2. Non-Interactive Mode
   You place commands in a file (a script) and run them all at once.

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Invoking Interactive vs. Non-Interactive Shells

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Interactive Example

$ ls
file1.txt  file2.txt
$ cd /tmp
$ pwd
/tmp

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Non-Interactive Example

1. Create a script script.sh:
   #!/bin/bash
   ls
   cd /tmp
   pwd
   
2. Make it executable and run:
   chmod +x script.sh
   ./script.sh
   # Output:
   # file1.txt  file2.txt
   # /tmp
   

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Comparing Shell Modes

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Why It Matters

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Inspecting PS1

$ echo "$PS1"
\u@\h:\w\$ 

#!/bin/bash
echo "$PS1"

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Best Practices for Shell Scripts

• Start with a shebang #!/usr/bin/env bash for portability.
• Use set -euo pipefail to catch errors early.
• Double-quote variable expansions to prevent word splitting: "$VAR".
• Explicitly source files when needed:
  source ~/.bashrc
  
• Test scripts in both modes if they must run interactively and non-interactively.

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Further Reading

• Bash Reference Manual
• Bash Startup Files
• Learn Shell