Read-only variables (readonly) in Bash Scripting - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the readonly command do in bash scripting?

It marks a variable as read-only, so its value cannot be changed or unset after being set.

beginner

How do you declare a read-only variable named MY_VAR with value hello?

Use readonly MY_VAR="hello" or MY_VAR="hello"; readonly MY_VAR.

beginner

What happens if you try to change a read-only variable in bash?

Bash will show an error message and will not allow the variable's value to be changed.

beginner

Can you unset a read-only variable in bash?

No, once a variable is marked read-only, it cannot be unset or deleted.

beginner

Why use read-only variables in bash scripts?

To protect important values from accidental changes, making scripts more reliable and easier to debug.

Which command makes a variable read-only in bash?

A export

B readonly

C declare -i

D unset

The readonly command marks variables as read-only.

What happens if you try to assign a new value to a read-only variable?

A The value changes successfully

B The variable is unset

C Bash throws an error and keeps the original value

D The script exits immediately

Bash prevents changing read-only variables and shows an error.

How do you declare a read-only variable after assigning it a value?

A readonly VAR=value

B VAR=value; export readonly VAR

C declare readonly VAR=value

D VAR=value; readonly VAR

You can assign first, then mark it read-only with readonly VAR.

Can you unset a variable marked as read-only?

A No, read-only variables cannot be unset

B Yes, with <code>unset</code>

C Only if you use <code>readonly -u</code>

D Only in interactive shells

Read-only variables cannot be unset or deleted.

Why is it useful to use read-only variables in scripts?

A To prevent accidental changes to important values

B To save memory

C To speed up script execution

D To allow variables to be shared between scripts

Read-only variables protect important values from accidental changes.

Explain how to create and use a read-only variable in bash scripting.

Think about how to protect a variable from changes.

Describe what happens if you try to modify or unset a read-only variable in bash.

Consider bash's behavior when protecting variables.