IntroToLinux

8. Advanced Environment Concepts

Variable Types:

Local Variables:

• Only available in current shell
• Not inherited by child processes

LOCAL_VAR="Only here"

Environment Variables:

• Available to current shell and child processes
• Created with export

export GLOBAL_VAR="Everywhere"

Special Variables:

• $? - Exit status of last command (0 = success)
• $$ - Process ID of current shell
• $! - Process ID of last background command

echo "Last command status: $?"
echo "Shell process ID: $$"

Variable Manipulation:

# String length
VAR="Hello World"
echo ${#VAR}        # Output: 11

# Substring
echo ${VAR:0:5}     # Output: Hello
echo ${VAR:6}       # Output: World

# Default values
echo ${VAR:-"default"}      # Use VAR or "default" if empty
echo ${VAR:="default"}      # Set VAR to "default" if empty

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