Special Characters in Bash

• $0: name of the script
• $1 to $9, arguments to the script. $1 is the first argument and so on.
• $@: all the arguments
• $#: number of arguments
• $?: return code of the previous command
• $$: process identification number (PID) for the current script

FYI:

• https://tldp.org/LDP/abs/html/special-chars.html
• https://missing.csail.mit.edu/2020/shell-tools/