How to Get Help With a Command from the Linux Terminal: 8 Tricks for Beginners & Pros Alike
Whether you’re an inexperienced terminal user or a grizzled veteran, you won’t always know the right thing to type into the Linux terminal. There are quite a few tools built into the terminal to help you along.
These tricks will help you find the command to use, figure out how to install it, learn how to use it, and view detailed information about it. None of these tricks require an Internet connection.
-h or –-help
If you’re not sure how to use a specific command, run the command with the -h or –-helpswitches. You’ll see usage information and a list of options you can use with the command. For example, if you want to know how to use the wget command, type wget –-help or wget -h.
This will often print a lot of information to the terminal, which can be inconvenient to scroll through. To read the output more easily, you can pipe it through the less command, which allows you to scroll through it with the arrow keys on your keyboard. For example, use the following command to pipe wget’s help output through less:
wget –-help | less
Press q to close the less utility when you’re done.
To find a specific option, you can pipe the output through the grep command. For example, use the following command to search for options that contain the word “proxy”:
wget –-help | grep proxy
If you’re not sure about a specific command’s name, an option, or a file name, you can use tab completion to help. Let’s say we want to run a command that we know starts with gnome-session, but we don’t know its exact name. We can type gnome-session into the terminal and press Tab twice to view commands that match the name.
Once we see the command, option, or file name we want, we can type a few more letters and press the Tab key again. If only one match is available, the Bash shell will fill it in for you. Tab completion is also a great way to save on keystrokes, even if you know what you want to type.
Command Not Found
If you know the command you want to use, but don’t know the package that contains it, you can type the command into the terminal anyway. Ubuntu will tell you the package that contains the command and show you the command you can use to install it.
Let’s say we wanted to use the rotate command to rotate an image. We could just type rotateinto the terminal and Ubuntu would tell us that we have to install the jigl package to get this command.
This feature was introduced by Ubuntu, and may have made its way into other Linux distributions. Traditionally, the shell displayed an unhelpful “command not found” message without any additional information.
The help command shows a short list of the commands built into the Bash shell itself.
The man command shows detailed manuals for each command. These are referred to as “man pages.” For example, if you wanted to view the man page for the wget command, you’d typeman wget. Man pages generally contain much more detailed information than you’ll get with the -h or –help options
Type man intro to see a detailed introduction to using the shell on Linux.
To search a man page, type a /, followed by your query, and press Enter. For example, to search a man page for the word shell, type /shell while reading the man page and press Enter.
Some programs don’t have man pages – or have very incomplete man pages – and store their documentation as info documents.
To view these, you’ll have to use the info command instead of the man command. That’s info tar instead of man tar.
The apropos command searches for man pages that contain a phrase, so it’s a quick way of finding a command that can do something. It’s the same thing as running the man -k command.
The whatis command shows a one-line summary of a command, taken from its man page. It’s a quick way of seeing what a command actually does.
whereis — Display information about the location of a command: the executable, the source code (if any), and the man pages.
which — Display which version of a command will execute (for when there are two, or more, commands with the same name installed on the system).
less /usr/share/doc — shows you more help documents if available.