How to interpret the bash command "usage" syntax?

Posted by raoulsson on Server Fault See other posts from Server Fault or by raoulsson
Published on 2010-03-20T20:42:57Z Indexed on 2010/03/20 20:51 UTC
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bash

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usage

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syntax

How exactly do you have to interpret the output of a commands "usage" output, in bash for example.

For example, on my OS X, cp gives me

usage: cp [-R [-H | -L | -P]] [-fi | -n] [-apvX] source_file target_file
       cp [-R [-H | -L | -P]] [-fi | -n] [-apvX] source_file ... target_directory

What does the nested options, like -H within -R, indicate?
Does upper and lower case have any meaning?
When is an argument optional, required?

I need to implement a telnet command line against a program of mine and I would like to get this straight.

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