Linux/Unix Commands to Know

Linux supports two different types of commands—shell commands and Linux commands. They may or may not prove interoperable with Unix commands.

Built-In Shell Commands

Shell commands are part of a shell. In other words, each shell (e.g., C Shell, Bourne Shell, and Korn Shell) incorporates a set of set of utilities. Though shell commands may vary from one shell to another, the commands within each shell stay the same across Linux distributions.

Execute shell commands at the shell prompt, the default of which is % for the C Shell, and $ for the Bourne Shell and the Korn Shell. To find out how to use a shell command, use the man command. The manpage of a shell command tells you how it's used in the currently active shell.

Unix Commands

Each Linux command is a separate executable program. They are written in C, or less likely, in other programming languages.

They reside in special directories for binary files, such as /user/bin. Directories that contain these Linux commands are listed in the search path, which the shells use to find them.

Commands may vary from one Linux distribution to another and one Unix flavor to another. Use these commands (original or added) the same way, independent of the shell you are currently in. Each Linux distribution system comes with a somewhat different set of commands.

Because Linux commands vary in syntax and usage from one distribution to another, use the man command to find out for sure how a command works on your particular platform.

Commands in Unix

Linux and Unix are related, but they're not identical. Some commands may work well in both a Unix and a Linux environment, but the points of departure are sufficiently broad that you cannot assume that any given program will work perfectly on every Linux distribution and every Unix variant.