String comparisons (=, !=, -z, -n) in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this Bash script snippet?

Consider the following Bash code:

str="hello"
if [ "$str" = "hello" ]; then
  echo "Match"
else
  echo "No match"
fi

What will be printed when this script runs?

Bash Scripting

str="hello"
if [ "$str" = "hello" ]; then
  echo "Match"
else
  echo "No match"
fi

A Syntax error

B No match

C Match

D Empty output

💡 Hint

Check how string equality is tested in Bash with single brackets.

The test [ "$str" = "hello" ] checks if the variable str equals the string "hello". Since it does, the script prints "Match".

💻 Command Output

intermediate

What does this Bash condition check?

What is the output of this Bash snippet?

str=""
if [ -z "$str" ]; then
  echo "Empty"
else
  echo "Not empty"
fi

Bash Scripting

str=""
if [ -z "$str" ]; then
  echo "Empty"
else
  echo "Not empty"
fi

A Not empty

B Empty

C Syntax error

D No output

💡 Hint

The -z test checks if a string is empty.

The -z operator returns true if the string is empty. Since str is empty, it prints "Empty".

💻 Command Output

advanced

What is the output of this Bash script with string inequality?

Analyze this Bash code:

str="world"
if [ "$str" != "hello" ]; then
  echo "Different"
else
  echo "Same"
fi

What will it print?

Bash Scripting

str="world"
if [ "$str" != "hello" ]; then
  echo "Different"
else
  echo "Same"
fi

A Different

B Same

C Syntax error

D No output

💡 Hint

The != operator checks if strings are not equal.

Since "world" is not equal to "hello", the condition is true and it prints "Different".

💻 Command Output

advanced

What happens when using -n with a non-empty string?

What is the output of this Bash snippet?

str="text"
if [ -n "$str" ]; then
  echo "Has content"
else
  echo "Empty"
fi

Bash Scripting

str="text"
if [ -n "$str" ]; then
  echo "Has content"
else
  echo "Empty"
fi

A Syntax error

B Empty

C No output

D Has content

💡 Hint

The -n test checks if a string is not empty.

The -n operator returns true if the string is not empty. Since str contains "text", it prints "Has content".

💻 Command Output

expert

What is the output of this Bash script with multiple string tests?

Consider this Bash script:

str1=""
str2="data"
if [ -z "$str1" ] && [ "$str2" = "data" ]; then
  echo "Condition met"
else
  echo "Condition not met"
fi

What will it print?

Bash Scripting

str1=""
str2="data"
if [ -z "$str1" ] && [ "$str2" = "data" ]; then
  echo "Condition met"
else
  echo "Condition not met"
fi

A Condition met

B Condition not met

C Syntax error

D No output

💡 Hint

Both conditions must be true for the && operator to pass.

str1 is empty, so -z "$str1" is true. str2 equals "data", so "$str2" = "data" is true. Both true means the script prints "Condition met".

Practice

1. Which operator in bash scripting checks if two strings are equal?

easy

A. Using = inside double brackets [[ ]]

B. Using -z to check string length

C. Using != inside double brackets [[ ]]

D. Using -n to check if string is not empty

Solution

1. Step 1: Understand string equality operator

   In bash, = inside [[ ]] compares if two strings are equal.

2. Step 2: Differentiate from other operators

   -z checks if string is empty, != checks inequality, -n checks non-empty string.

3. Final Answer:

   Using = inside double brackets [[ ]] -> Option A

4. Quick Check:

   String equality = = [OK]

Hint: Use = inside [[ ]] to check if strings are equal [OK]

Common Mistakes:

• Confusing = with -z or -n
• Using = outside [[ ]] without quotes
• Mixing != with = for equality

2. Which of the following is the correct syntax to check if a variable var is not empty in bash?

easy

A. [ -z "$var" ]

B. [ "$var" = "" ]

C. [ -n "$var" ]

D. [ $var != "" ]

Solution

1. Step 1: Understand -n operator

   -n returns true if the string length is greater than zero (not empty).

2. Step 2: Check syntax correctness

   Using quotes around $var prevents errors if variable is empty or contains spaces.

3. Final Answer:

   [ -n "$var" ] -> Option C

4. Quick Check:

   Not empty check = -n [OK]

Hint: Use [ -n "$var" ] to test if var is not empty [OK]

Common Mistakes:

• Using -z instead of -n for not empty
• Forgetting quotes around variable
• Using = "" to check emptiness incorrectly

3. What will be the output of this bash script snippet?

var="hello"
if [[ "$var" != "world" ]]; then
  echo "Not world"
else
  echo "World"
fi

medium

A. Not world

B. World

C. Syntax error

D. No output

Solution

1. Step 1: Evaluate string comparison

   Variable var is "hello", which is not equal to "world".

2. Step 2: Determine which branch runs

   The condition [[ "$var" != "world" ]] is true, so it echoes "Not world".

3. Final Answer:

   Not world -> Option A

4. Quick Check:

   hello != world -> Not world [OK]

Hint: If strings differ, != condition is true [OK]

Common Mistakes:

• Confusing = and != operators
• Missing quotes causing syntax errors
• Assuming else branch runs when condition is true

4. Identify the error in this bash snippet that checks if input is empty:

if [ -z $input ]; then
  echo "Empty"
else
  echo "Not empty"
fi

medium

A. Using -z instead of -n

B. Missing quotes around $input in test

C. Using single brackets instead of double brackets

D. No error, script is correct

Solution

1. Step 1: Check variable quoting in test

   Variable $input is not quoted, which can cause errors if empty or contains spaces.

2. Step 2: Understand correct syntax

   Quotes around $input like "$input" are needed to safely test emptiness.

3. Final Answer:

   Missing quotes around $input in test -> Option B

4. Quick Check:

   Always quote variables in tests [OK]

Hint: Always quote variables in [ ] tests to avoid errors [OK]

Common Mistakes:

• Forgetting quotes around variables
• Thinking -z and -n are interchangeable
• Believing single brackets can't test strings

5. You want to write a bash script that prints "Empty string" if variable text is empty, and "Has content" otherwise. Which snippet correctly does this?

hard

A. if [ "$text" != "" ]; then echo "Empty string"; else echo "Has content"; fi

B. if [[ "$text" = "" ]]; then echo "Has content"; else echo "Empty string"; fi

C. if [ -n "$text" ]; then echo "Empty string"; else echo "Has content"; fi

D. if [[ -z "$text" ]]; then echo "Empty string"; else echo "Has content"; fi

Solution

1. Step 1: Understand -z usage

   -z "$text" returns true if text is empty.

2. Step 2: Check echo outputs match condition

   If empty, print "Empty string"; else print "Has content". if [[ -z "$text" ]]; then echo "Empty string"; else echo "Has content"; fi matches this logic correctly.

3. Final Answer:

   if [[ -z "$text" ]]; then echo "Empty string"; else echo "Has content"; fi -> Option D

4. Quick Check:

   -z empty -> print "Empty string" [OK]

Hint: Use if [[ -z "$var" ]] for empty string check [OK]

Common Mistakes:

• Swapping outputs for empty and non-empty cases
• Using = "" without quotes or wrong logic
• Confusing -n and -z meanings