Unveiling the Power of the 'whatis' Command (with Examples)

The whatis command is a powerful utility in Unix-like operating systems that provides users with brief, one-line descriptions of other commands found in the system’s manual pages. It serves as a quick reference tool that helps users understand the general purpose of a command without needing to delve into extensive manual entries. By consulting the whatis tool, newcomers and seasoned users alike can enhance their command-line efficiency and knowledge. Here, we will explore various use cases of the whatis command to demonstrate its versatility and utility.

Use Case 1: Display a Description from a Man Page

Code:

whatis command

Motivation:

Imagine you’re navigating your terminal and come across an unfamiliar command. Understanding what a command does is crucial before attempting to execute it, particularly to avoid unintended outcomes. This is where the whatis command steps in. By issuing the whatis command followed by the unfamiliar command’s name, you can get a concise outline of its purpose—equipping you with the information necessary to decide whether to explore further.

Explanation:

• command: This is the placeholder for the actual command you want to learn about. By supplying the name of a system command, such as ls, echo, or cp, whatis retrieves the corresponding description directly from the system’s manual pages.

Example Output:

ls (1)               - list directory contents

Use Case 2: Don’t Cut the Description Off at the End of the Line

Code:

whatis --long command

Motivation:

Sometimes, the basic whatis output may truncate longer descriptions, leading to incomplete information on more complex commands. When you require a more comprehensive overview that isn’t truncated, the --long option becomes essential. This option extends the output to display the full description available on the manual’s first line, making certain that you see every detail provided.

Explanation:

• --long: This argument instructs whatis to refrain from cutting off the description at the end of the line. It’s particularly useful when the standard description isn’t sufficient to understand the command fully.

Example Output:

ls (1)               - list directory contents in many formats including columns, horizontal/long, with entries sorted by

Use Case 3: Display Descriptions for All Commands Matching a Glob

Code:

whatis --wildcard net*

Motivation:

When dealing with multiple commands that begin with the same prefix, such as when working with network utilities (netstat, netcat, etc.), it can become cumbersome to check each one individually. By using pattern matching through globbing, users can list all relevant commands at once. This is incredibly efficient for discovering available commands in a specific category without having to specify each name explicitly.

Explanation:

• --wildcard: This option allows for pattern matching using shell-style wildcards. Here, net* is a glob pattern that matches any command starting with “net”.

Example Output:

netcat (1)           - TCP/IP swiss army knife
netgen (1)           - circuit netlist comparison tool

Use Case 4: Search Man Page Descriptions with a Regular Expression

Code:

whatis --regex 'wish[0-9]\.[0-9]'

Motivation:

Advanced users often seek commands that fit a more complex pattern, especially when dealing with versioned tools or similar command variations. In scenarios where shell-style globbing is insufficient, utilizing a regular expression provides granular control and precision. It enables a sophisticated search across command descriptions, perfect for pinpointing exact matches based on intricate criteria such as specific software versions.

Explanation:

• --regex: This argument employs regular expressions, a powerful tool for matching a wide range of text patterns.
• 'wish[0-9]\.[0-9]': This regular expression matches any command name starting with “wish” followed by a number, a dot, and another number, capturing typical versioning patterns.

Example Output:

wish8.6 (1)          - Simple Tcl/Tk interactive shell
wish8.5 (1)          - Simple Tcl/Tk interactive shell

Use Case 5: Display Descriptions in a Specific Language

Code:

whatis --locale=en command

Motivation:

In diverse working environments or for internationally reaching applications, it’s crucial to access information in the correct language. Systems can be configured to support multiple languages. Thus, specifying a language for command descriptions becomes vital for non-native speakers or users working in multilingual teams. It ensures that the information provided is both comprehensible and actionable.

Explanation:

• --locale=en: This specifies the language desired for the command’s description. Here, en is the locale code for English. Changing this code targets a different language as supported by the system’s manual pages and locale settings.

Example Output:

ls (1)               - list directory contents

Conclusion:

With the adaptable functionality of the whatis command, users can greatly improve their understanding and navigation across Unix-based systems. By learning about individual command purposes, accessing detailed descriptions, performing pattern-based searches, and selecting preferred languages, whatis proves itself an indispensable ally in command-line mastery.