The Relationship Between Bash and SH; What's The Difference?

The terms Bash and SH refer to two different types of shell environments used in Linux and other Unix-like operating systems. While they both serve the purpose of interacting with the system through command-line interfaces (CLI), they have notable differences in terms of features, compatibility, and functionality.

1. Origins and Compatibility

• SH (Bourne Shell): The Bourne shell, commonly referred to as sh, was developed by Stephen Bourne at AT&T Bell Labs in the 1970s. It became the standard shell for Unix systems, providing basic functionalities such as file manipulation, variable management, and scripting. Its design focused on simplicity and portability, making it a versatile tool for system administrators and users alike. SH is typically available on nearly all Unix-based systems, even today.

• Bash (Bourne Again Shell): Bash is an enhanced version of the Bourne shell. Developed by Brian Fox in 1987 for the GNU Project, Bash incorporates features from other shells like C Shell (csh) and Korn Shell (ksh), in addition to expanding on the original Bourne shell's capabilities. While Bash is fully compatible with sh and can run most Bourne shell scripts without modification, it includes additional features that make it more user-friendly and versatile for modern system usage.

2. Features and Enhancements

• Bash: One of the primary reasons Bash is preferred over SH is its expanded set of features. These include:

  • Command-line editing: Bash supports advanced command-line editing, allowing users to move the cursor and edit commands using keyboard shortcuts (e.g., using the arrow keys to navigate through previous commands).
  • Job control: Bash provides the ability to suspend and resume jobs (e.g., using Ctrl+Z to suspend a process and fg to resume it).
  • Arrays: Bash allows for more complex data structures, including indexed arrays and associative arrays, which are not available in sh.
  • Brace Expansion: Bash supports brace expansion, which allows users to generate arbitrary strings based on patterns, improving script conciseness and flexibility.
  • Advanced scripting capabilities: Bash offers powerful tools such as command substitution, extended pattern matching, and built-in string manipulation, making it more suitable for complex scripting tasks.

• SH: By contrast, the original sh shell has fewer built-in features compared to Bash. It lacks features like command-line editing and job control, and its scripting capabilities are simpler. While this makes it more lightweight and portable, it also means that writing complex scripts can be more cumbersome in SH. However, sh scripts are typically more compatible across different Unix-like systems because sh is considered the "lowest common denominator" shell.

3. Portability and Use Cases

• SH: SH is favored for portability, especially in situations where scripts need to run across a wide range of Unix-like systems. Because SH has been part of Unix for so long, it's typically available on nearly all Unix-based systems. Scripts written in pure SH syntax tend to be more portable and can be executed without modifications on different systems, making SH the go-to choice for system administrators who require maximum compatibility.

• Bash: While Bash is widely available on Linux distributions and many Unix-like systems, it is not as universally present as SH. There may be cases, such as on certain minimal or embedded systems, where Bash is not installed by default. However, since many Linux distributions use Bash as the default shell, it is often the preferred choice for modern system scripting and daily interactive use due to its rich set of features.

4. Scripting and Interactivity

• SH: Scripts written for SH are typically more focused on basic automation tasks and are often simpler in structure. Given its limited feature set, scripts may require more manual workarounds for tasks that would be straightforward in Bash. However, SH scripts are usually more compatible across different systems, making them ideal for system-wide installation scripts or software that needs to be distributed widely.

• Bash: Bash provides a more interactive experience with its advanced command-line editing and job control. It's excellent for personal use, administrative tasks, and when writing more complex scripts that require advanced functions like arithmetic operations, loops, or conditional branching. Bash also supports functions and more sophisticated ways to handle errors, making it suitable for creating highly maintainable and robust scripts.

5. Conclusion

In summary, Bash is a superset of the sh shell, offering enhanced features and a more interactive, user-friendly experience. However, sh remains valuable for its simplicity and portability, particularly in environments where compatibility across diverse systems is critical. While Bash is often the preferred choice for users and administrators on modern Linux systems, sh retains its importance in the context of system compatibility and for users who need minimal, universal shell scripts.