Bash vs sh: Key Differences and When to Use Each

The sh shell is a basic, POSIX-compliant shell mainly used for simple scripts and maximum compatibility, while bash is an enhanced shell with more features like arrays, functions, and improved scripting syntax. Use bash for advanced scripting and interactive use, and sh when you need portability across different Unix systems.

Quick Comparison

This table summarizes the main differences between bash and sh shells.

Factor	sh	bash
Type	Basic POSIX shell	Enhanced Bourne Again Shell
Compatibility	Highly portable across Unix systems	Mostly compatible but with extensions
Features	Limited scripting features	Supports arrays, functions, arithmetic, and more
Interactive Use	Minimal interactive features	Rich interactive features like tab completion
Default Shell	Default on many Unix systems	Default on many Linux distributions
Script Syntax	Strict POSIX syntax	Extended syntax with more commands

Key Differences

sh is the original Unix shell designed for simple scripting and maximum portability. It follows the POSIX standard strictly, which means scripts written for sh will run on almost any Unix-like system without modification. However, it lacks many modern conveniences.

bash stands for Bourne Again SHell and is a superset of sh. It adds many features like arrays, improved variable handling, arithmetic operations, and better interactive use such as command history and tab completion. This makes bash more powerful for writing complex scripts and for daily command line use.

While bash scripts often run fine under sh, scripts using bash-specific features will fail in sh. Therefore, choosing between them depends on whether you prioritize portability or advanced features.

Code Comparison

Here is a simple script that prints numbers 1 to 3 using a loop in bash.

bash

#!/bin/bash
for i in {1..3}; do
  echo "Number $i"
done

Output

Number 1
Number 2
Number 3

sh Equivalent

The equivalent script in sh uses a different loop syntax because sh does not support brace expansion.

sh

#!/bin/sh
i=1
while [ "$i" -le 3 ]; do
  echo "Number $i"
  i=$((i + 1))
done

Output

Number 1
Number 2
Number 3

When to Use Which

Choose bash when you want to write scripts with advanced features like arrays, functions, or need a rich interactive shell with command history and tab completion. It is ideal for Linux systems and personal use where bash is available.

Choose sh when you need maximum portability across different Unix and Unix-like systems, especially for simple scripts that must run everywhere without modification. It is best for system scripts and environments where bash may not be installed.

Key Takeaways

Use bash for powerful scripting and interactive shell features.

Use sh for maximum portability and simple scripts.

bash supports advanced syntax like arrays and brace expansion; sh does not.

Scripts using bash-specific features won't run in sh without modification.

Choose the shell based on your environment and script requirements.