shellscommonly

Shellscommonly is not an established term; it is used here to refer to the set of command-line shells commonly encountered across operating systems. A shell is a user interface that serves as a command interpreter, executing user commands, launching programs, and providing scripting capabilities. The phrase acts as a neutral shorthand for comparing features, syntax, and compatibility among widely used shells.

Shells offer interactive prompts, job control, environment variables, and the ability to construct pipelines and scripts with conditionals and loops. They vary in language syntax and in how strictly they adhere to portability. POSIX sh compatibility is a common baseline for scripting, but many shells add nonportable extensions.

Common shells include Bash (Bourne Again Shell), which dominates Linux and many Unix systems for both interactive use and scripting; Zsh, valued for advanced completion and customization; Fish, designed for user friendliness and its own scripting language; Tcsh, an enhanced C shell with command-line editing; Dash, a lightweight POSIX-compliant shell used for speed in scripts; and PowerShell, a cross-platform, object-oriented shell from Microsoft. macOS ships with Zsh by default (as of Catalina); earlier versions used Bash. Windows supports Command Prompt and PowerShell, with Windows Subsystem for Linux enabling POSIX shells.

When choosing a shell, users weigh factors such as interactivity, script portability, ecosystem tooling, and cross-platform needs. POSIX sh remains a portable baseline, while Bash, Zsh, Fish, and PowerShell offer richer features that can affect script compatibility and learning curves.