How to use variables in Bash scripts

Variables let a Bash script name values that would otherwise be repeated, such as a user name, retry count, file path, or job label. A script is easier to adjust when those values live in one assignment or come from arguments instead of being copied through every command.

Bash assigns a variable with name=value and reads it with $name or ${name}. The braces mark the variable boundary when text follows the value, and quotes around expansions keep spaces and empty strings from being split into separate command arguments.

A short script can combine a default argument, a numeric counter, and a derived log filename without drifting into a parameter-expansion reference. Running it with no argument and with a quoted argument confirms that the fallback value, explicit input, braces, and quoted expansions behave as expected.

1. Create a script that assigns variables and prints their expanded values.

   variables-demo.sh

   #!/usr/bin/env bash
   set -euo pipefail
    
   name=${1:-operator}
   count=3
   job_name="backup"
   log_file="${job_name}-${count}.log"
    
   printf "name=%s\n" "$name"
   printf "count=%s\n" "$count"
   printf "job=%s\n" "$job_name"
   printf "log=%s\n" "$log_file"

   Do not add spaces around = in a variable assignment. name=value assigns a variable, while name = value asks the shell to run a command named name.

2. Check the script syntax before running it.

   $ bash -n variables-demo.sh

   No output means Bash did not find a parse error.

3. Run the script without an argument to verify the default value.

   $ bash variables-demo.sh
   name=operator
   count=3
   job=backup
   log=backup-3.log

4. Run the script with a quoted name to verify that the argument stays one value.

   $ bash variables-demo.sh "Ops Team"
   name=Ops Team
   count=3
   job=backup
   log=backup-3.log

5. Keep variable expansions quoted unless the script intentionally needs word splitting or glob expansion.

   printf "name=%s\n" "$name"

   Unquoted variables can turn an empty value into a missing argument or split a value with spaces into several arguments.