Variables

Variables store data for the shell or user.

There are two types of variables used in the Bash shell:

  • Local – Only in current session
  • Environment – Available to shell and child processes

1. Local variables

  • Local vars exist only in current shell
  • They do not affect other commands or applications.
  • Lost when terminal closes
  • Commonly used for user tasks and written in lowercase.
  • Set a variable using: variable=value (creates or updates it).

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2. Environment variable

  • Available system-wide (all shells)
  • Automatically recreated when a new shell opens
  • Common examples: PATH, HOME, HISTSIZE

Example:

  • Export a local variable → environment variable : export var1 → makes it global
  • Create + export in one line : export var2='Hosain'
  • Combine values of variables : var1=$var1' '$var2 'JK'
  • Remove an environment variable : unset var1

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3. Path Variables

  • PATH = directories where shell looks for commands
  • Directories separated by :
  • If command not in PATH → command not found error
  • Always append $PATH to prevent losing old paths

Example 

[COMMAND] > [FILE]       # structure
echo $PATH               # Show current PATH
PATH=/video/movie:$PATH  # Add /video/movie to PATH
echo $PATH               # Verify update