Special Variables

There are a few other variables that the system sets for you to use as well.

• $0 - The name of the Bash script.
• $1 - $9 - The first 9 arguments to the Bash script. (As mentioned above.)
• $# - How many arguments were passed to the Bash script.
• $@ - All the arguments supplied to the Bash script.
• $? - The exit status of the most recently run process.
• $$ - The process ID of the current script.
• $USER - The username of the user running the script.
• $HOSTNAME - The hostname of the machine the script is running on.
• $SECONDS - The number of seconds since the script was started.
• $RANDOM - Returns a different random number each time is it referred to.
• $LINENO - Returns the current line number in the Bash script.

**$1, $2, ...**

The first, second, etc command line arguments to the script.

**variable=value**

To set a value for a variable. Remember, no spaces on either side of =

**Quotes " '**

Double will do variable substitution, single will not.

**variable=$( command )**

Save the output of a command into a variable

**export var1**

Make the variable var1 available to child processes.