1

How do I understand what the various options/flags mean?

For example:

1) uname -a - What does -a denote here?

2) pyang -f - What does -f denote here?

I just want to understand if there is some reference/doc that tells the usage of these? Please clarify.

Improve this question
2
  • 3
    For the first man uname. What is pyang? Commented Sep 3, 2016 at 15:02
  • pyang is library that validates the yang models Commented Sep 3, 2016 at 15:13

2 Answers 2

Reset to default
1

With almost all Linux commands, I think the fastest and easiest first course of action is to append "--help" to the command. This gives you a good summary, which is often enough.

If you need more details, the man command is a good second choice.

For example:

$ uname --help 

Usage: uname [OPTION]... Print certain system information. With no OPTION, same as -s. -a, --all print all information, in the following order, except omit -p and -i if unknown: -s, --kernel-name print the kernel name -n, --nodename print the network node hostname -r, --kernel-release print the kernel release -v, --kernel-version print the kernel version -m, --machine print the machine hardware name -p, --processor print the processor type (non-portable) -i, --hardware-platform print the hardware platform (non-portable) -o, --operating-system print the operating system --help display this help and exit --version output version information and exit
Improve this answer
6
  • 'command --help' works only with executables, not for shell builtin commands, functions and aliases... Commented Sep 3, 2016 at 16:53
  • @Neni - Well, not functions and aliases, of course, but builtins? Like ls, etc? Works with bash just fine. Commented Sep 3, 2016 at 16:54
  • 'read --help', 'cd --help', 'alias --help', ... doesn't work in bash. 'ls' is not a builtin, it is an executable, run: 'which ls' Commented Sep 3, 2016 at 16:58
  • @Neni - OK, fair enough. But the error actually prints out the usage, so it still is a quick way to try first. Commented Sep 3, 2016 at 17:01
  • 1
    I don't think this answer deserved a down vote. The OP specifically asked how to get information about uname and pyang and these are not builtins. Yes, an answer which also mentions builtins might seem more complete, but could also overwhelm someone asking such a question. Nothing wrong with this answer IMHO. Commented Sep 3, 2016 at 17:23
1

In UNIX/Linux Shells, there are four different types of commands:

1. executables: compiled binaries or scripts 2. shell builtin commands 3. shell functions 4. aliases

If you encounter an unknown command, the first thing is to check its type. Let's examine a few examples for each type:

type <command> # indicates the commands type -------------- type find # find is /usr/bin/find --> executables type cd # cd is a shell builtin type dequote # dequote is a function type ls # ls is aliased to 'ls --color=auto'

Having the information of the command type, you can get help, description and usage of the command and it's options:

<command> --help # help for executables --> find --help help <command> # help for shell builtins --> help cd man <command> # manual page for the specific command

Following commands are useful for information gathering as well.

whatis <command> # display a very brief description of the command which <command> # display an executables location

In the example above, ls is aliased, but what is ls really?

whatis ls help ls # doesn't work --> ls is not a shell builtin command ls --help # works --> ls is an executable / compiled binary which ls # /bin/ls --> ls is an executable / compiled binary

There are thousands of commands to explore:

ls /bin # list a few executables ls /usr/bin # list more executables enable -p # list all available shell builtin commands declare -f # list all defined functions alias # list all defined aliases

Now let's examine the uname command:

type uname # uname is /bin/uname --> executable whatis uname which uname uname --help # see the meanings of the options, e.g. -a man uname # read the manual page for uname

Do the same for the pyang command...

Improve this answer
2
  • Kind of overwhelming for someone that is a rank beginner, though. The first several examples give no useful information for "uname", one of his specific topics, whereis my suggestion for a first try gives exactly what he wanted. Commented Sep 3, 2016 at 17:37
  • I didn't mean you, I meant the original poster. He is the one that may get overwhelmed by too much detail. I didn't intend to write a thesis on every possibility - I saw your answer, so I didn't need to duplicate your information, I thought it was more useful to add what I felt was missing. Sorry if you felt insulted. Commented Sep 3, 2016 at 17:47

You must log in to answer this question.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.