Meta answer:<p>apropos and man (these are for Unix-like systems, a.k.a POSIX systems (loosely speaking). But you may find them on Windows too, via Cygwin and its ilk (e.g. MKS Toolkit (still exists?), UWin, and maybe a few others) and nowadays the Windows Subsystem for Linux too (WSL - maybe). IIRC that last one is Windows 10 only, though.<p>This is because the apropos command lets me find commands for some purpose (apropos some_word) and the man command then lets me learn how to use them. [1]. (Of course you can look up books and the Internet too, but the man command is online on the same system you are working on.) Apropos may not work for every word you try it with, but even with the commands that it works for (not all may be in its database), it is useful, and enough to be going on with for a long time, in terms of learning and exploring. You can learn about the existence of a lot of new (to you) commands using apropos, and then try them out, and use them regularly if it makes sense for your needs.<p>Of course there are more in that meta category too, such as find (powerful tool to find files matching various criteria in the file system - combine it with xargs), awk and sed (multipurpose little languages which integrate beautifully with the shell), and so on.<p>Related to the man command: Here is a simple utility to help with creating and reading man pages for topics - coincidentally I had blogged about it a few days ago, after I mentioned it to a consulting client:<p>m, a Unix shell utility to save cleaned-up man pages as text:<p><a href="https://jugad2.blogspot.in/2017/03/m-unix-shell-utility-to-save-cleaned-up.html" rel="nofollow">https://jugad2.blogspot.in/2017/03/m-unix-shell-utility-to-s...</a><p>Mentioning it to him made me think of blogging about it, although I first wrote it many years ago on a Unix box. It will work on any Unix variant that has the shell (sh / ksh / bash), the man command (and the corresponding man pages installed) and the col command. May work on other shells such as fish, tcsh or zsh too, but I haven't checked. If not working directly, it probably can be easily ported to them.<p>So, taking the examples of the commands mentioned above, this is the first command to run, using m:<p>m apropos man<p>which will generate in ~/man, the man pages (in text format) for the apropos and man commands, and then:<p>m find xargs awk sed<p>which will do the same for those other commands, all of which are powerful and frequently used in Unix systems.