Backticks vs braces in Bash
The `` is called Command Substitution and is equivalent to $() (parenthesis), while you are using ${} (curly braces).
So all of these expressions are equal and mean "interpret the command placed inside":
joulesFinal=`echo $joules2 \* $cpu | bc`joulesFinal=$(echo $joules2 \* $cpu | bc)# v v# ( instead of { v# ) instead of }While ${} expressions are used for variable substitution.
Note, though, that backticks are deprecated, while $() is POSIX compatible, so you should prefer the latter.
From man bash:
Command substitution allows the output of a command to replace thecommand name. There are two forms:
$(command) or `command`
Also, `` are more difficult to handle, you cannot nest them for example. See comments below and also Why is $(...) preferred over ... (backticks)?.
They behave slightly differently in specific case:
$ echo "`echo \"test\" `"test$ echo "$(echo \"test\" )""test"so backticks silently remove the double quotes.