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[ Linux Command Encyclopedia](#) * * * units is a powerful unit conversion tool in Linux systems that can handle conversions between various physical quantities, including length, weight, temperature, speed, time, etc. This command-line tool is particularly suitable for engineers, scientists, and technical personnel who need to perform complex unit conversions. units command features: * Supports conversion of over 3000 units * Can perform compound unit calculations (e.g., converting watt-hours to joules) * Allows users to define custom units * Provides interactive and command-line usage modes * * * ## Install units Command Most Linux distributions do not install units by default and require manual installation: ## Example # Debian/Ubuntu systems sudo apt-get install units # CentOS/RHEL systems sudo yum install units # Fedora systems sudo dnf install units # Arch Linux systems sudo pacman -S units After installation, you can verify if it was successful with the following command: units --version * * * ## Basic Usage The units command has two main usage modes: interactive and non-interactive. ### Interactive Mode Enter interactive mode by typing the `units` command directly: ## Example $ units 2861 units, 109 prefixes, 109 nonlinear units You have: Enter the unit you want to convert after the prompt, for example: You have: 1 mile You want: km * 1.609344 / 0.62137119 In the output: * The number after `*` represents the multiplication factor (1 mile = 1.609344 km) * The number after `/` represents the reciprocal factor (1 km = 0.62137119 miles) ### Non-interactive Mode You can complete conversions directly in the command line: units "1 mile" "km" The output is the same as in interactive mode. * * * ## Common Unit Conversion Examples ### Length Unit Conversion ## Example # Inches to centimeters $ units "12 inch""cm" *30.48 /0.032808399 # Feet to meters $ units "6 feet""meters" *1.8288 /0.54680665 ### Temperature Unit Conversion ## Example # Fahrenheit to Celsius $ units "98.6 degF""degC" *37 /0.027027027 # Kelvin to Celsius $ units "300 K""degC" *26.85 /0.037243908 ### Speed Unit Conversion ## Example # Miles per hour to kilometers per hour $ units "60 mph""kph" *96.56064 /0.010356187 # Knots to meters per second $ units "15 knots""m/s" *7.7166667 /0.12958963 ### Data Storage Unit Conversion ## Example # Gibibytes to megabytes $ units "1 gibibyte""megabyte" *1073.7418 /0.00093132257 # Note: units uses binary prefixes (base 1024) by default # To use decimal prefixes (base 1000), use 'megabytes' instead of 'megabyte' * * * ## Advanced Features ### Compound Unit Conversion units can handle complex compound units: ## Example # Kilowatt-hours to joules $ units "1 kWh""joules" *3600000 / 2.7777778e-07 # Pounds-force per square inch to pascals $ units "1 psi""pascal" *6894.7573 /0.00014503774 ### Custom Units You can define your own units in the `~/.units` file. For example, add a "football field" unit: footballfield 100 m Then you can use it: ## Example $ units "1 footballfield""km" *0.1 /10 ### Currency Conversion (Requires Internet) units supports currency conversion, but requires internet access to get the latest exchange rates: $ units "100 USD" "EUR" Note: Currency conversion may not be available on some systems or may require additional configuration. * * * ## Practical Tips 1. **View available unit list**: Enter `?` or `help` in interactive mode to view help information 2. **Fuzzy search**: After entering part of a unit name, press Tab to auto-complete 3. **History**: In interactive mode, you can use up/down arrows to view command history 4. **Precise output control**: Use the `-v` parameter to display more detailed information units -v "1 lightyear" "km" 1. **Check unit compatibility**: Use the `-c` parameter to only check if units are compatible without performing conversion units -c "joules" "watt hours" * * * ## Frequently Asked Questions ### Why are some unit conversion results inaccurate? units uses a predefined unit database, and some conversions (especially currencies) may have precision limitations or use approximate values. For precise scientific calculations, it is recommended to consult professional reference materials. ### How to update the unit database? The unit database is usually located at `/usr/share/units/definitions.units`. You can manually edit this file or wait for system updates. ### Can batch conversion be performed? You can write shell scripts combined with the units command to achieve batch conversion: ## Example #!/bin/bash for value in 1 2 5 10; do result=$(units "$value feet""meters"|awk'NR==1 {print $2}') echo"$value feet = $result meters" done * * * ## Summary units command is a powerful and flexible unit conversion tool in Linux systems, suitable for various scientific, engineering, and daily calculation scenarios. Through the introduction in this article, you should have mastered: 1. Basic installation and usage of the units command 2. Unit conversion techniques for common physical quantities 3. Advanced features such as compound unit conversion and custom units 4. Practical tips and problem-solving methods in real applications To learn more about the units command