Bash, and shell scripting languages in general, refer to the process of evaluating variables and other parameters such as $1 as parameter expansion.
The safest way to use parameter expansion is to prefix the name of the variable with a dollar sign as part of a double-quoted string:
$ realname='Bash User' $ printf '%s\n' "Hello, $realname." Hello, Bash User.
If you need to distinguish the variable name from characters around it, you can use curly brackets:
$ printf '%s\n' "__Hello, ${realname}__"
__Hello, Bash User__
This prevents Bash from trying to expand a variable named realname__, with two trailing underscores.
Note that if you expand a variable that doesn't exist, by default Bash does not issue any warnings; it just ...
