What's the difference between ${varname} and $varname in a shell scripts

Question

I have a simple question but I wonder what is the difference between ${varname} and $varname ?

I use both but I don\'t see any difference w

Answer 1

They are the same in a basic case, but using ${varname} gives more control and ability to work with the variable. It also skips edge cases in which it can create confusion. And finally, it enables variable expansion as described in Shell Parameter Expansion:

The ‘$’ character introduces parameter expansion, command substitution, or arithmetic expansion. The parameter name or symbol to be expanded may be enclosed in braces, which are optional but serve to protect the variable to be expanded from characters immediately following it which could be interpreted as part of the name.

When braces are used, the matching ending brace is the first ‘}’ not escaped by a backslash or within a quoted string, and not within an embedded arithmetic expansion, command substitution, or parameter expansion.

The basic form of parameter expansion is ${parameter}. The value of parameter is substituted. The braces are required when parameter is a positional parameter with more than one digit, or when parameter is followed by a character that is not to be interpreted as part of its name.

Let's see a basic example. Here, the use of ${} allows us to do something that a simple $ does not. Consider we want to write $myvar + "blabla"::

$ myvar=23
$ echo $myvar
23
$ echo $myvarblabla
                        <--- the variable $myvarblabla doesn't exist!
$ echo ${myvar}blabla
23blabla