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A command-line interpreter is software that reads text commands, works out what they mean, and runs them or passes them to another program. It is commonly called a shell. Bash, Windows Command Shell (cmd.exe), and PowerShell are examples. The terminal is the interface through which you interact with a shell; it is not the interpreter itself.
What does a command-line interpreter do?
A command-line interpreter accepts commands written as text and evaluates them according to its own command language. In an interactive session, you type at a prompt and the shell responds. Microsoft describes this kind of command shell as an interactive command-line interface and a Read-Eval-Print Loop (REPL): it reads input, evaluates it, then produces a result. Microsoft Learn: What is a command shell?
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The shell can handle commands built into its language or launch a separate program. It may also provide features such as variables, functions, and flow control, so commands can be combined into scripts and automated tasks. GNU describes Bash as both a command interpreter and a programming language. GNU Bash Reference Manual: What is a shell?
How does a shell process commands?
- Input arrives: A person types a command in a terminal, or the shell receives commands from a script file or command string.
- The shell evaluates it: It interprets the text using its own syntax and applies relevant language features, such as variables or control flow.
- The requested action runs: The shell carries out a built-in operation or starts an external program, then presents the result through the interface.
Shells can therefore be used both interactively and non-interactively. A script lets the interpreter read and process commands without someone entering every command at a prompt. GNU Bash Reference Manual: What is a shell?
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Is a terminal the same as a shell?
No. A terminal is the user-facing text interface or host for a command-line application. A shell is the software that interprets the commands entered through that interface. A command-line tool is generally a separate program launched from the shell to perform a particular task. Microsoft notes that people sometimes use these terms interchangeably, but they refer to different parts of the interaction. Microsoft Learn: What is a command shell?
A prompt is simply the visible cue that the shell is ready for input. It is not the interpreter. For example, Windows documents prompt as a command, while describing cmd.exe as the command interpreter. Microsoft Learn: cmd
Examples of command-line interpreters
| Interpreter | Context and defining detail |
|---|---|
| Bash | The GNU operating system’s shell, or command-language interpreter. GNU says Bash is intended to conform to the IEEE POSIX Shell and Tools portion of IEEE Std 1003.1. GNU Bash Reference Manual: What is Bash? |
Windows Command Shell (cmd.exe) |
Microsoft’s cmd command starts a new instance of the Windows command interpreter, cmd.exe. Microsoft Learn: cmd |
| PowerShell | A command-line shell and scripting language used for automation. Windows documentation lists PowerShell alongside Command Shell as a Windows command-line shell. Microsoft Learn: Running commands in the shell Microsoft Learn: Windows commands |
Do commands work the same in every interpreter?
No. Each shell has its own command language and syntax. Bash follows a Unix shell lineage and aims for compatibility with the POSIX Shell and Tools standard; PowerShell has its own scripting language; and Windows Command Shell uses its own command environment and batch-file conventions. A command or script written for one interpreter may need changes—or may not work at all—in another. GNU Bash Reference Manual: What is Bash? Microsoft Learn: Running commands in the shell Microsoft Learn: Windows commands
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