- 01Setting up (what you'll need)
- 02Your first shell script (echo)
- 03Using variables
- 04Command-line arguments ($1, $2 ...)
- 05Branching (the if statement)
- 06Repeating (the for loop)
- 07Repeating (the while loop)
- 08Writing your own function
- 09Working with arrays
- 10Command substitution ($())
- 11Working with strings (parameter expansion)
- 12Reading from standard input (read)
- 13Exit status and && / ||
- 14Pipes and redirection
- 15The case statement
- 16Arithmetic ($(( )))
- 17The basics of grep, sed and awk
- 18Argument checks and error handling
- 19Function return values and exit codes
- 20[Project] Build a small log-tallying script
Arithmetic ($(( )))
This lesson covers arithmetic expansion, the way a shell script does numeric calculation.
Writing $((expression)) performs arithmetic. Ordinary variable expansion ($var) alone treats everything as a string, so calculation needs its own notation.
The sample code totals two variables with total=$((a + b)).
A common early stumble is trying to calculate with plain variable expansion, as in total=$a+$b. That simply assigns the string "10+20" — no calculation happens.
In professional work, this arithmetic is used for simple sums: totalling how many items were processed, counting loop iterations.
๐งช This site can't compile or run Shell Script directly, so it checks on the spot whether what you typed matches the reference code (scoring happens entirely in your browser โ nothing is sent anywhere).