Logical operators (-a, -o, !) in Bash Scripting - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the '-a' operator do in bash scripting?

The '-a' operator means AND. It checks if both conditions on its sides are true.

beginner

What is the purpose of the '-o' operator in bash?

The '-o' operator means OR. It checks if at least one of the conditions is true.

beginner

What does the '!' operator do in bash conditional expressions?

The '!' operator means NOT. It reverses the result of the condition that follows it.

intermediate

How would you write a condition to check if a file exists AND is readable using '-a'?

You write: [ -e filename -a -r filename ] which means the file exists AND is readable.

intermediate

Why should you be careful when mixing '-a' and '-o' in the same test expression?

Because '-a' and '-o' have different precedence and can cause unexpected results. It's safer to use separate tests or parentheses.

In bash, what does '[ -f file -a -w file ]' check?

A File exists and is writable

B File exists or is writable

C File does not exist and is writable

D File is not writable

The '-a' means AND, so both conditions must be true: file exists (-f) AND file is writable (-w).

What does the '!' operator do in '[ ! -e folder ]'?

A Checks if folder is readable

B Checks if folder exists

C Checks if folder does NOT exist

D Checks if folder is writable

'!' negates the condition, so it checks if the folder does NOT exist.

Which operator means OR in bash test expressions?

A -o

B !

C -a

D &&

'-o' means OR, checking if either condition is true.

Why might mixing '-a' and '-o' in one test be risky?

A They always return false

B They only work in scripts, not command line

C They are deprecated

D They have different precedence which can cause logic errors

Different precedence can cause unexpected results, so it's better to separate conditions.

How do you write a condition to check if a file is NOT empty using '!'?

A [ -s ! file ]

B [ ! -s file ]

C [ ! -e file ]

D [ -s file ]

'-s' checks if file size is greater than zero; '!' negates it, so '[ ! -s file ]' means file is empty.

Explain how to use '-a', '-o', and '!' in bash conditional tests with simple examples.

Think about checking file properties with AND, OR, and negation.

Describe a real-life scenario where you might use logical operators '-a', '-o', and '!' in a bash script.

Imagine checking if a file is ready to be processed.