Using the command line (Bash)

Command line with bash (Bourne Again Shell)

A Unix shell and command language.

• bash is scripting language that is referred to as a shell
  • because it sits around the kernel making it easy to interact with
• Often default shell

• bash can be seen as a program that finds and runs other programs
• The command-line interface: the bash prompt

$

The prompt

[info]$ program word1 word2 word3 […]

• [info] is configurable, and usually tells you who you are, on what system, and where in the file system.

Example: 

[bjornc@rackham3 linux_tutorial]$

• •  To change this see: How to customize Bash prompt in Linux Links to an external site.

• The program to run is the first word
  • All words are separated by spaces
• The following words can be arguments to the program, file names, flags etc...

Program, flags, and files

• Input to the program:
  • Flags: specific single letters or words that change the behaviour of a program.
  • Arguments: text given to the program when started, e.g. file names.
  • Terminal input: text given to the program while it runs.

• Output from the program:
  • Most Linux programs output to the terminal.
  • Some programs also write to files.

Example bash command

•   Terminal screen shows the output
  

Tab Completion

Whenever you’re writing a path or filename on the bash prompt, you can strike the ‘tab’ key to
ask Bash to complete what you’re writing.

• Get in the habit of this — it will save you many hours!

Editing files with text editors

• gedit (graphical user interface — GUI, needs X-server)

• Graphical editor within MobaXterm

• nano (keyboard shortcuts shown on-screen)
  • Cheatsheet: http://staffwww.fullcoll.edu/sedwards/nano/UsefulNanoKeyCommands.html Links to an external site.
    • (^ = Ctrl, M = meta key)
      • Windows M = Alt
      • On Mac: in the Terminal.app go to Preferences -> Settings -> Keyboard and turn on "Use option as meta key": then M = Alt

• vim (fast and powerful, once you learn it)
  • on UPPMAX started with command "vi"

  • 1. Insert mode (type like normal text editor. Press "i" for insert mode)

  • 2. Command mode (give commands to the editor to get things done . Default or Press ESC for command mode)

  • Cheatsheet: https://coderwall.com/p/adv71w/basic-vim-commands-for-getting-started Links to an external site.

• gvim vim with a GUI, lots of features
  • very Fast!

• emacs
  • fast and powerful, once you learn it
  • Cheatsheet: https://www.gnu.org/software/emacs/refcards/pdf/refcard.pdf Links to an external site.
    • (C = Ctrl)
  • also with GUI
  • $ emacs –nw
  •  keeps you in terminal window.

• When starting the graphical versions, add "&" to be able to use the command line while program is open.
  • $ gedit &
  • If not, you can "Ctrl+z" and type bg to send program to background.

• Try them out and pick one favorite editor!

Typical sources of error

• Capitalization matters in file names and program names

• Spaces matter.
  • Always have a space after the program name.
  • Don’t add spaces within file names.
• Check that you are in the right place in the file system.
• File permissions. Check that the right read, write and execute permission are set.

Caution!!

Beware of overwriting files and deleting the wrong ones.

• There is no undo for

• • copy (cp)
  • move (mv)
  • remove (rm)

• Tip: make "rm" ask if you really want to erase:
  • Within a session: Type in the command prompt

    alias rm='rm -i'

  • Override asking with 

    rm –f <filename>

  • Edit file ".bashrc" in /home directory by adding the alias line for this to start everytime in a new shell
• This will also work for mv and cp!

• If you do destroy your data, email UPPMAX support, we MAY be able to help.