test command and [ ] syntax in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of test command with string comparison

What is the output of this bash script snippet?

Bash Scripting

if test "abc" = "abc"; then echo success; else echo fail; fi

A syntax error

B success

C test: command not found

D fail

💡 Hint

The test command checks if two strings are equal.

The test command with '=' compares strings. Since both are "abc", the condition is true and 'success' is printed.

💻 Command Output

intermediate

Behavior of [ ] with numeric comparison

What will this script print?

Bash Scripting

if [ 5 -gt 3 ]; then echo yes; else echo no; fi

A yes

B no

C syntax error

D command not found

💡 Hint

The -gt operator compares numbers inside [ ].

5 is greater than 3, so the condition is true and 'yes' is printed.

💻 Command Output

advanced

Effect of missing spaces in [ ] test

What error or output does this script produce?

Bash Scripting

if [5 -eq 5]; then echo ok; else echo fail; fi

A fail

B syntax error

C ok

D bash: [5: command not found

💡 Hint

Remember that spaces are required around [ and ] in bash tests.

Without spaces, bash treats '[5' as a command, which does not exist, causing a command not found error.

💻 Command Output

advanced

Difference between test and [ ] with file existence

What is the output of this script if file.txt exists?

Bash Scripting

if test -f file.txt; then echo found; else echo missing; fi

A syntax error

B missing

C found

D command not found

💡 Hint

The -f option checks if a file exists and is a regular file.

If file.txt exists as a regular file, test -f returns true and 'found' is printed.

💻 Command Output

expert

Complex condition with test and [ ] combined

What does this script print if variable VAR is empty?

Bash Scripting

VAR=""; if test -z "$VAR" && [ 1 -eq 1 ]; then echo pass; else echo fail; fi

A pass

B fail

C syntax error

D command not found

💡 Hint

test -z checks if a string is empty; && combines conditions.

VAR is empty, so test -z "$VAR" is true, and [ 1 -eq 1 ] is also true, so 'pass' is printed.

Practice

1. What does the [ -f filename ] test check in a bash script?

easy

A. If filename is a directory

B. If filename is empty

C. If filename is executable

D. If filename exists and is a regular file

Solution

1. Step 1: Understand the -f test

   The -f option in [ ] checks if the file exists and is a regular file (not a directory or special file).

2. Step 2: Compare with other options

   -d checks for directory, -x for executable, and -s for non-empty file, so they don't match.

3. Final Answer:

   If filename exists and is a regular file -> Option D

4. Quick Check:

   -f means regular file check [OK]

Hint: Remember: -f means regular file exists [OK]

Common Mistakes:

• Confusing -f with -d for directories
• Forgetting spaces inside [ ]
• Using filename without quotes causing errors

2. Which of the following is the correct syntax to test if variable var is equal to string hello in bash?

easy

A. [ $var = hello ]

B. [ $var == hello ]

C. [ "$var" = "hello" ]

D. [ "$var" == hello ]

Solution

1. Step 1: Check quoting rules

   Variables should be quoted to avoid errors if empty or contain spaces, so "$var" is correct.

2. Step 2: Check operator correctness

   Single equals = is POSIX compliant for string comparison inside [ ]. Double equals == works in [[ ]] but not always in [ ].

3. Final Answer:

   [ "$var" = "hello" ] -> Option C

4. Quick Check:

   Quote variables and use = inside [ ] [OK]

Hint: Always quote variables and use = inside [ ] [OK]

Common Mistakes:

• Not quoting variables causing syntax errors
• Using == inside [ ] which may fail
• Missing spaces around brackets

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

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

medium

A. Empty

B. Not Empty

C. Syntax Error

D. No output

Solution

1. Step 1: Understand the -z test

   -z returns true if the string length is zero (empty string).

2. Step 2: Check variable value

   Variable var is set to empty string "", so [ -z "$var" ] is true and the if branch runs.

3. Final Answer:

   Empty -> Option A

4. Quick Check:

   -z tests empty string [OK]

Hint: Use -z to check empty strings [OK]

Common Mistakes:

• Not quoting variable causing errors
• Confusing -z with -n
• Expecting else branch to run

4. Identify the error in this bash condition:

if [ $num -gt 10 ]; then
  echo "Greater"
fi

medium

A. Missing spaces inside [ ]

B. Variable $num should be quoted

C. Wrong operator for numeric comparison

D. Missing then keyword

Solution

1. Step 1: Check variable usage in test

   When using variables in [ ], they should be quoted to avoid errors if empty or unset.

2. Step 2: Analyze the given code

   The code uses $num unquoted. If num is empty, the test becomes invalid syntax.

3. Final Answer:

   Variable $num should be quoted -> Option B

4. Quick Check:

   Always quote variables in [ ] to avoid syntax errors [OK]

Hint: Quote variables inside [ ] to prevent errors [OK]

Common Mistakes:

• Not quoting variables causing syntax errors
• Confusing numeric and string operators
• Forgetting spaces around brackets

5. You want to check if a file data.txt exists and is not empty before processing it in a script. Which condition correctly does this?

hard

A. [ -f data.txt ] && [ -s data.txt ]

B. [ -f data.txt -o -s data.txt ]

C. [ -f data.txt && -s data.txt ]

D. [ -f data.txt ] || [ -s data.txt ]

Solution

1. Step 1: Understand the tests

   -f checks if file exists and is regular file; -s checks if file size is greater than zero (not empty).

2. Step 2: Choose correct logical operator

   To require both conditions, use logical AND. Inside a single [ ], use -a; or chain separate tests with &&. Using && directly inside [ ] causes syntax error.

3. Step 3: Analyze options

   The option with && inside single [ ] has syntax error. Chained tests with && are clear and reliable. Options using -o or || apply OR logic, incorrect.

4. Final Answer:

   [ -f data.txt ] && [ -s data.txt ] -> Option A

5. Quick Check:

   Use && to combine separate [ ] tests [OK]

Hint: Use separate [ ] with && for AND conditions [OK]

Common Mistakes:

• Using -o or || which means OR, not AND
• Using && inside a single [ ] (syntax error)
• Not checking file size with -s