whatis

Understanding the whatis Command

The whatis command searches the /usr/share/man/whatis database (or a similar location depending on your distribution) for short descriptions of commands, functions, and other manual pages. It provides a one-line summary, perfect for quickly grasping the purpose of a command before diving into its full manual page.

The basic syntax is straightforward:

whatis command_name

Replace command_name with the command you want information about.

Practical Examples

Let’s look at some practical examples to illustrate the functionality of whatis:

1. Getting Information about a Common Command:

Let’s find out what the ls command does:

whatis ls

This will likely output something like: ls (1) - list directory contents

The (1) indicates that the description comes from section 1 of the manual pages, typically for user commands.

2. Searching for Multiple Commands:

You can search for multiple commands at once by simply listing them:

whatis ls cp mv rm

This will provide concise descriptions for each command in a separate line.

3. Handling Ambiguous Names:

If a command name is ambiguous, whatis will list all matching entries:

For example, if you are unsure about the exact name of a command related to users, trying whatis user might give you many results.

whatis user

This will probably return multiple entries related to user management commands.

4. Whatis and Wildcard Characters:

The whatis command also supports wildcard characters (*). This allows you to search for commands that match a pattern.

For example, to find information about all commands related to networking, you could use:

whatis net*

5. Exploring the limitations:

The whatis database is not always perfectly up-to-date and might not contain information about every command on your system, especially newly installed ones. If a command is not found, it returns no output; it doesn’t report an error message.

6. The importance of the man database:

The accuracy and completeness of whatis relies heavily on a well-maintained man database. If your system’s manual pages are outdated or incomplete, whatis’s results will reflect that. You can update the man database using your distribution’s package manager. (e.g., apt update && apt upgrade on Debian/Ubuntu, yum update on CentOS/RHEL)

7. Using apropos for more detailed searches:

While whatis offers quick summaries, the apropos command provides more detailed search capabilities based on keywords in the manual pages, allowing for more flexible searching.