Environment

$PATH: Environment variable that stores the search path for executables.

Example:

> echo $PATH
/home/felix/bin:/usr/local/bin:/usr/bin:/usr/X11R6/bin:/.

echo: Display a line of text.

Example:
  
  echo hallo
  echo $HOME

env: List environment variables.

Example:

> env
.
.
.
LANG=en_US
HOME=/home/felix
OSTYPE=linux
WINDOWMANAGER=/usr/X11R6/bin/gnome
LOGNAME=felix
PRINTER=lp
INFOPATH=/usr/local/info:/usr/share/info:/usr/info
DISPLAY=:0.0
.
.

which: Shows the full path of (shell) commands.

Example:

> which emacs
/usr/bin/emacs

export: Set an environment variable in the bash shell.

Example:

    export PATH=${PATH}:~/special-bin