Unix commands begin with a command name, often followed by flags and arguments some of which are optional. The generic syntax is:
command [flags] argument1 argument2 ...
Normally the flags are preceded by a hyphen to prevent them from being
interpreted as a filename. For example, in the command line
ls -l avhrr
ls is the program called, -l is the flag, and avhrr
is the argument. This command tells the computer to list (in long
format) the file called avhrr or, if avhrr is
a directory, to list all the files in the directory avhrr.