The Command-line (shell)

The real power of Linux/Unix systems is the command line.

Many programs and facilities are available through graphical options on Linux, but all programs and facilities can be accessed by the command line, also known as the shell.
Graphical interfaces are good for reduced data, when analysing processed data.
web services and curses-mode screens are halfway between command-line and grapihical interface.
However for "heavy-lifting", the command-line is much more convenient
Obvious examples include when you need to work with large numbers of files or want to automate processes.
It's common to talk about "fear of the commandline", our aim is to reduce this.

Anatomy of a Command

<command> <options/parameters> <arguments>

first word you supply on the command line is interpreted by the system as a command, an operation.
Items that appear after that on on the same line are separated by spaces.
Most commands have options available that will alter the way the command functions.
after the options we have what are called arguments, often these are input files.
With some commands you don't need to issue any parameters or arguments. This is because you are using the default settings.
To know the default settings the documentation must be read.

If a command runs successfully, it often will not report anything back to you
You can of course tell by the nature of the putput files it produced.
If a command is unsuccessful, it will report an error. Most of the time, these are informative, even if a bit cryptic.
However, if you forgot to specify the input file, you should be able to interpret that.