Getting Help

The immense power of the command line is accompanied by an astonishing amount of complexity. This chapter will point you at some resources available within the system itself to help you navigate this complexity.

Man Pages

Man pages short for manual pages will provide you with a basic overview of a command, its options and features.

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Try it out by checking what man has to say about itself.

Info

While man pages are a great source of information they do have some shortcomings . For example there is no easy way to navigate between man pages. info provides structured documentation based on topics rather then commands. Info style documentation is usually more suited to learning a topic while man pages often offer a more in-depth view of commands and features.

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Try info on its own and with a command as argument.

Other sources of help

The --help option

Most commands come with a built in help. Often this help can be viewed by calling the command with the --help or -h flag.

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Give it a try . Call ps --help

Third party documentation

Most distribution have a dedicated location for third party vendors to store documentation for their software. Typical places include /usr/share/doc and /usr/doc. Refer to the documentation of your distribution for this path.

Finding commands and documentation

whatis

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whatis is a command that, well use it to find out what it does.

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Now try whatis on ls.

You will see that there seem to be multiple commands that list directory content. Why? Long story short because their are two major UNIX variants and most Linux distributions contain the commands of both.

But now we have an issue. Which one of these is actually executed? Let's explore this.

whereis

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Use whereis to figure out where ls keeps its binaries sources and man pages.

Note that there usually is only one binary but two man pages here. This is because ls can be used with the details laid out by either of the man pages. Sadly this is often not the case.

locate

locate can be used to find any file or directory. It uses a pre-generated database which contains all files and directories present on the system at time of database generation. Generation of this database is typically done once a day. With root privileges you can update the locate database using the updatedb command. Be aware that locate is not present in all distributions by default.