Bash Arithmetic and Numeric Input
Validate a bounded decimal count before calculating.
How it works
Bash arithmetic is integer arithmetic with a shell-specific grammar. Input can be interpreted as an expression, and leading zeros may trigger a different numeric base. Do not treat arbitrary input as an arithmetic expression. First require a small decimal representation, then explicitly select base ten. Choose another language or tool when floating-point arithmetic is required.
Run the code
Reviewed with Git for Windows Bash 5.2.37. Open Git Bash, save the download with LF line endings in a separate learning folder, check it with bash -n lesson-name.sh, then run bash lesson-name.sh using the actual filename. Bash 4 or newer is required for the full course. Linux-only notes identify unavailable tools or POSIX behaviour. There is no Bash browser runner; Apache and MySQL are not required.
This complete example was executed in the stated local review environment.
Example
#!/usr/bin/env bash
set -u
set -o pipefail
export LC_ALL=C
count="08"
[[ $count =~ ^[0-9]{1,3}$ ]] || exit 2
value=$((10#$count))
total=$((value * 3))
[[ $total -eq 24 ]] || exit 1
printf "Three batches: %d sheets\n" "$total"
Expected result
Three batches: 24 sheets
The format check allows only one to three ASCII digits, keeping the range bounded and excluding expression syntax. The 10# prefix gives a decimal interpretation to 08. Production constraints may require a smaller business maximum too. Arithmetic evaluation is not a substitute for validating a request or file field.
Primary technical reference: Bash documentation.