Values from Commands: $( ) and $(( ))

$( ) runs a command and puts what it prints into another command or a variable, such as today's date in a backup's name, and $(( )) works out whole-number arithmetic, such as an age or a count plus one.

Updated

Cheat sheet for the lesson Values from Commands: $( ) and $(( )): $( ) runs a command and puts what it prints into another command or a variable, such as today's date in a backup's name, and $(( )) works out whole-number arithmetic, such as an age or a count plus one.
Category
Bash
Level
Apprentice
Tags
arithmetic-expansion, command-substitution, date, linux, unix