Basics

Learn the basics.

• Basics
  • The prompt
    • Output redirect
    • Chaining commands
    • Useful shortcuts
  • General Commands
    • Getting help
    • System
  • Variables
    • Common variables
    • Shell variables
    • Environment variables
    • Both var types
    • Persistent env vars
    • More

The prompt

The prompt will usually look something like this username@hostname: ~$ or this [username@hostname ~]$ . You can type commands after the prompt.

If you’re in sudo mode, # will be displayed instead of $. ~ is your current working directory.

Output redirect

You can redirect the output of a command to a file or something else with appending >PATH. You can redirect errors with 2>PATH.

Chaining commands

• <cmd1> || <cmd2>: only execute cmd2 if cmd1 failed
• <cmd1> && <cmd2>: only execute cmd2 if cmd1 was successful
• <cmd1> ; <cmd2>: run both commands no matter the result of the first one
• <cmd1> | <cmd2>: feed the results of cmd1 into cmd2 (“piping”)
• <cmd1> &: run the command in background

Useful shortcuts

• Ctrl+A: jump to start of line
• Ctrl+E: jump to end of line
• Ctrl+C: stop/abort/exit command
• Ctrl+Z: interrupt process
• Ctrl+D: exit session/terminal

General Commands

• exit: end a terminal (or ssh) session
• history: view the command history
• clear: empty terminal
• reset: reset terminal (use when issues arise regarding weird symbols)
• echo <args>: print arguments to default output

Getting help

• <command> --help: common argument for most commands
• man [group] <command>: get man pages (group is a number, e.g. 1 stands for user commands)
• info <command>: get info pages

System

• shutdown <time> "<message>"
  • <time>: z. B. 22:00, +5, now
  • -r: reboot
  • -F: Dateisystem bei nächstem Neustart überprüfen
  • -c: cancel
  • -p: explizit ausschalten (in virtualisierten Systemen z. T. notwendig)
  • -f: force (bis zu 2x angeben)
• halt: same as shutdown now
• poweroff: same as shutdown now
• init 0: same as shutdown now
• reboot: same as shutdown -r now

Variables

Common variables

• $SHELL: path to the current shell
• $HOME: path to the current user’s home directory
• $HOSTNAME: name of current device
• $? exit code of last command

Shell variables

• set: print all shell vars
• set | more: print shell vars
• set | grep VAR=: get a specified shell var
• $VAR: use a shell var
• echo $VAR: print a shell var
• VAR=CONTENT: set a shell variable

Environment variables

• printenv: print all environment vars
• printenv VAR VAR2...: print one or more environment vars
• export VAR=CONTENT: set an environment var

Both var types

• unset VAR: unset a shell or environment variable
• export VAR: promote a shell to an environment variable
• export -n VAR: demote an environment to a shell variable

Persistent env vars

To make environment variables persistent, their export statements have to be saved in files.

User-specific vars can be stored in ~/.bashrc (accessable in non-login bash shells), ~/.bash_profile (acessible only by Bash) or ~/.profile (accessible in any Bourne shell).

System-wide vars can be stored in /etc/environment (accessible by every shell) or /etc/profile and the files in /etc/profile.d/ (accessible by bash login shells; using files in the folder is recommended).

More

• export PATH="$PATH:<path-to-add>": add a path to PATH