Comparison Of Different Unix Shells

What is a Shell and Why Do You Need One

A shell is a user interface that provides an environment for accessing a computer’s services. It is the outer layer between the user and the operating system kernel and is used to execute other programs. Shells provide a command line interface (CLI) to give instructions to the operating system using lines of textual commands.

The main purposes and functionalities of a shell include:

Providing a CLI for user interaction
Executing commands and scripts
Managing processes and applications
Controlling jobs and tasks
Customizing user environments
extending system functionality and flexibility

Some of the most common and popular Unix shells include:

Bourne shell (sh)
Bash (Bourne Again shell)
Z shell (zsh)
C shell (csh)
Korn shell (ksh)
Fish (Friendly Interactive Shell)

Choosing a suitable shell allows users to maximize their productivity by using an interface aligned with their workflow, customization needs, and style of usage.

Core Differences Between Major Shells

While all shells have common basic functionalities, there can be significant syntactic, configurational, customization, and extensibility variations between them. Understanding these core differences allows users to select the best option for their specific needs.

Syntax Variations

The syntax refers to the set of rules and structures used for constructing commands the shell will interpret. For example:

Bash uses $ for variables by default while csh/tcsh uses nospaces
Spaces delimit arguments in bash, while csh/tcsh uses newlines
Bash uses { and } for grouping commands while tcsh uses endif
Fish uses more natural language syntax with autosuggestions and syntax highlighting

Default Configurations

The out-of-the-box settings and environment vary significantly between shells in terms of:

Interactive behavior and prompts
Variable assignments
Aliases enabled
Permissions restrictions
Supported data types

For example, bash enables vi command line editing by default while zsh provides emacs mode instead.

Customization and Extensibility

All shells allow some degree of customization but with differing capabilities in areas like:

Theming prompts, colors, and appearance
User-defined aliases, functions, shortcuts
Configuring bindings, completions, histories
Loading extensions and frameworks
Programming custom plugins and scripts

For instance, Oh My Zsh provides a popular community framework for customizing zsh with 1000+ plugins while fish relies on a simpler built-in plugin manager system.

Code Examples of Differences

Here is a simple “hello world” script with variations for different shells:

# Bash
echo "Hello world!"

# Csh
echo "Hello world!"

# Zsh 
echo "Hello world!"

# Fish
echo "Hello world!"

While trivial in this example, the syntax divergence grows quickly for more complex scripting use cases.

Bash – The Default Shell

Bash (Bourne Again SHell) is the most widely used shell, serving as the default shell on most Linux distributions and MacOS. It has gained popularity due to:

Being open-source, free, and included by default on Linux and MacOS
Inheriting useful features from earlier Bourne shell versions while adding improvements
Providing effective CLI interactivity for command execution
Having a large community providing manuals, tutorials, configs, and scripts

Pros

Ubiquitous – pre-installed on most systems
Familiar syntax inherited from Bourne shell
Lightweight and fast for daily use
Feature-rich for intermediate to advanced usage
Extensive community support and resources

Cons

Less user-friendly to beginners compared to fish/zsh
Outdated assumptions on syntax leading to inconsistencies
Limited capabilities without extensions compared to newer shells
Frustrating default configurations

When to Use Bash

Good cases to use bash include:

You need maximum portability across different *nix systems
You are already an experienced bash user
You have existing bash scripts and muscle memory
You only need a basic shell without advanced customization
You are working with servers, containers, or restricted environments allowing only bash

Zsh – A Powerful Alternative

Zsh or Z Shell is an extended Bourne shell alternative known for advanced feature capabilities. Key highlights include:

Advanced command line editing, completion, and correction
Powerful globbing and wildcard expansions
User-customizable framework via Oh My Zsh
Backwards compatibility with bash scripts
Theming options for prompts, colors, and appearance

Oh My Zsh Framework Overview

Oh My Zsh provides a popular open source framework for managing zsh configuration allowing:

1000+ plugins offering functionality enhancements
160+ theme options affecting prompts, colors, etc
Module system for organizing customizations
Simple installation using git, curl, or install scripts

When to Use Zsh

Good cases for using zsh include:

You want advanced customization capabilities
You are looking for bells & whistles like autocompletion
You enjoy tweaking shells to perfection
You use the terminal heavily and value efficiency

Fish – The User-Friendly Shell

Fish (Friendly Interactive Shell) focuses on usability simplicity and beauty as guiding design principles with features like:

Syntax highlighting for commands as you type
Autosuggestions to reduce typing
Intuitive tab completions
Excellent man pages for discoverability
Out of the box prompts showing useful system info

Unique Features for Usability

Additional unique beginner-friendly capabilities fish offers include:

Web-based configuration for simplicity
No files required reducing hidden complexity
Package manager integrations (e.g. with pip, npm, gem)
Man page autocompletions

When Fish is a Good Option

Great scenarios to use fish:

You are new to the command line world
You want to avoid arcane syntax and configs
You prioritize human friendliness over customization
You need to write only simple scripts

Choosing the Best Shell For You

At the end of the day, personal preference guided by individual workstyles and needs is the major factor for choosing a shell. However, here are some key considerations:

Considerations for Personal and Production Use

Daily interactive shell needs may differ from scripting shell requirements. Key questions to ask:

Will this be used for a server or production environment?
Do others need to use, share, or inherit configs and scripts?
How much effort can be allocated to tweaking and customization?
What degree of programming capabilities are needed?

Assessing Individual Needs and Priorities

Understanding personal preferences across:

Ease of use vs configurability
Compatibility vs latest features
Speed vs aesthetics
Scripting vs interactivity
Server coverage vs workstation utility

Allows matching a shell appropriately with day-to-day requirements.

Recommendations for Common Scenarios

Migrating from bash: Try zsh for added capabilities or fish for simplified experience.
Programming and scripting: Stick with bash for portability or use zsh for cleaner extensions.
Command line newbie: Fish is the most beginner-friendly option.
Sysadmin / DevOps: Bash for baseline access, zsh for advanced customization.
Tweaking and eye candy lover: Fully customized zsh with oh-my-zsh plugins and themes.