Hello, I'm slowly learning linux. Quite often i see a dash and a letter after commands, I'm not even sure what the actual name of them are called.

For example: Today i had to delete some directories from my server, I went to computer hope and it told me which command to use. Although it doesn't explain what the dash and letter are.

This is the command:

rm -r mydir

Here's what i know:

rm= remove directory
mydir = name of my directory that i want deleted

what it doesn't say what the "-" or "r" means

Where can i get info on what these are and what they mean, i've seen the often in other commands


thanks,

Those are flags. They provide extra information to the program that can change its functionality. You can see all of the flags available in a program in its "man" (short for manual) page. In this case, open a terminal and run "man rm". This page will tell you what the "rm" program does, how it works, and the available flags/options. For "rm", the "-r" flag means:
You can see that there are multiple ways to set this flag as well. You could run "rm -r", "rm -R", or even "rm --recursive", all will do the same thing.

2 members found this post helpful.

i see! now i understand, i will be using the man command often, i find i learn better if i know what every single letter means,

thank you!

Unfortunately that's a tad ambitious (if taken literally).

There are a lot(!) of cmds and each one has its own list of flags (aka options, switches).
Moreover any given one eg '-r' may or may not exist for a given cmd and if it does, it may well have a different meaning.

However, you should definitely look up all the ones you are thinking of using

HTH & Welcome to LQ

Using the man command is key for a lot of this. Down the bottom you see related commands, you also see things like result codes which you can check from the shell or check within a script.

Also welcome to LQ!

Also note that many commands have two alternatives. For instance, -r might have a less-cryptic alternative, say, --recursive.

A single dash means that the option consists of a single character, and these might be combined behind one dash. For instance, ls -ra is equivalent to ls -r -a.

A double dash means that the option consists of a word.

All of this is left entirely to the discretion of the implementor of the command, and will be documented (if at all) in the man page ... e.g. man ls ... which is also left entirely to the discretion of the implementor.

Also, if you want a quick check of most of these commands you can useThe rm being the command (any command) with the 'help' flag.
It's quicker than the man pages but not as comprehensive.

$ rm --help

(as previously listed) or

$ man rm

It tends to be documented. Although don't assume the -r means the same thing for all things, it doesn't. So always check if you're unsure.