The whatis command is a Linux utility designed to provide a quick overview of a command’s function. It delivers a concise description, helping users understand the command’s purpose without needing to consult the full manual page. This tool is invaluable for system administrators, developers, and anyone who frequently uses the command line.

Written in C, whatis extracts its information from the Linux manual pages (man pages). It’s commonly pre-installed on most Linux distributions, making it readily accessible.

Installation

While whatis is generally included in standard Linux installations, you can install it using your distribution’s package manager if it’s missing.

Debian/Ubuntu

Open a terminal and use the following command to install whatis on Debian or Ubuntu systems:

sudo apt-get install man-db

Red Hat/CentOS

On Red Hat or CentOS, use this command in the terminal:

sudo yum install man-db

Arch Linux

For Arch Linux, run this command in the terminal:

sudo pacman -S man-db

Usage

The whatis command is straightforward. Simply type `whatis` followed by the command you want to learn about.

Example 1: Getting the Description of `ls`

To see what the ls command does, enter this:

whatis ls

The output will be similar to:

ls (1) - list directory contents

This tells you that ls is used for listing directory contents.

Example 2: Using Wildcards

You can also use wildcards to find commands matching a pattern. For example, to find commands starting with “net”:

whatis net*

The output might look like this:

netcat (1) - TCP/IP swiss army knife
netstat (8) - Print network connections, routing tables, interface statistics, masquerade connections, and multicast memberships

This shows commands like netcat and netstat that match the “net” prefix.

Similar Commands

Other tools offer related functionality:

• apropos: Searches man pages for commands matching a keyword.
• man: Displays the full manual page for a command.
• help: Provides help for shell built-in commands.

While these tools share similarities, whatis is unique in its concise summaries.

Automation Scripts

Here are examples of how whatis can be used in scripts:

Script 1: Descriptions for Multiple Commands

This script takes a list of commands and prints their descriptions using whatis.

#!/bin/bash

commands=("ls" "cd" "mkdir")

for command in "${commands[@]}"
do
  description=$(whatis $command)
  echo "Description of $command: $description"
done

Script 2: Searching with a Keyword

This script prompts the user for a keyword and finds commands matching it.

#!/bin/bash

read -p "Enter a keyword: " keyword

matching_commands=$(whatis -w $keyword)

echo "Matching commands:"
echo "$matching_commands"

Script 3: Creating a Command Cheat Sheet

This script generates a cheat sheet of all commands on the system.

#!/bin/bash

whatis -s 1,8 -w "*" > commands.txt

echo "Command cheat sheet generated successfully."

List of Possible Functions and Constants

Command/Constant	Description
ls	List directory contents
cd	Change the current working directory
mkdir	Create a new directory
rm	Remove files or directories
cp	Copy files and directories
mv	Move or rename files and directories
grep	Search for patterns in files
sed	Stream editor for filtering and transforming text
awk	Pattern scanning and processing language
ssh	Secure shell client for remote login

Conclusion

whatis is a valuable tool for any Linux user. Its ability to quickly provide command descriptions saves time and improves command-line efficiency. Its conciseness separates it from other tools, aiding users in rapidly understanding command functionality. Whether you’re beginner or expert whatis can significantly increase your productivity when navigating Linux’s command line interface.

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