File test operators (-f, -d, -e, -r, -w, -x) in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this script?

Consider a file named example.txt that exists and is readable but not executable. What will this script print?

Bash Scripting

if [ -r example.txt ] && [ ! -x example.txt ]; then
  echo "Readable but not executable"
else
  echo "Other"
fi

A Readable but not executable

B Other

C Syntax error

D No output

💡 Hint

Think about what -r and -x check for in a file.

The -r operator checks if the file is readable, and -x checks if it is executable. Since the file is readable but not executable, the condition is true and prints "Readable but not executable".

💻 Command Output

intermediate

What does this script output if mydir is a directory?

Given mydir is a directory, what will this script print?

Bash Scripting

if [ -d mydir ]; then
  echo "Directory exists"
else
  echo "Not a directory"
fi

A Not a directory

B No output

C Syntax error

D Directory exists

💡 Hint

The -d operator checks if the path is a directory.

The -d operator returns true if the file exists and is a directory. Since mydir is a directory, it prints "Directory exists".

💻 Command Output

advanced

What error does this script produce?

What error will this script produce when run?

Bash Scripting

if [ -f ]; then
  echo "File exists"
fi

A File exists

B bash: [: -f: unary operator expected

C No output

D Syntax error: unexpected token

💡 Hint

Check if the -f operator requires an argument.

The -f operator needs a filename to check. Without it, the test command reports 'unary operator expected'.

💻 Command Output

advanced

What is the output of this script if script.sh is executable and writable?

Given script.sh is executable and writable, what will this script print?

Bash Scripting

if [ -x script.sh ] && [ -w script.sh ]; then
  echo "Executable and writable"
else
  echo "Other"
fi

A Executable and writable

B Other

C No output

D Syntax error

💡 Hint

Remember what -x and -w check for.

The -x operator checks if the file is executable, and -w checks if it is writable. Both conditions are true, so it prints "Executable and writable".

💻 Command Output

expert

What is the value of variable result after running this script?

Assuming file.txt exists and is readable but not writable, what is the value of result after this script runs?

Bash Scripting

if [ -e file.txt ]; then
  if [ -r file.txt ] && [ ! -w file.txt ]; then
    result="read-only"
  else
    result="other"
  fi
else
  result="missing"
fi

A missing

B other

C read-only

D Syntax error

💡 Hint

Check the file existence and permissions carefully.

The file exists (-e true), is readable (-r true), and not writable (! -w true), so result is set to "read-only".

Practice

1. Which file test operator checks if a path is a regular file in a bash script?

easy

A. -e

B. -f

C. -d

D. -x

Solution

1. Step 1: Understand the meaning of each operator

   -f checks if the path is a regular file, -d checks for directory, -e checks if the path exists, and -x checks if the file is executable.

2. Step 2: Match the operator to the question

   The question asks for the operator that checks if a path is a regular file, which is -f.

3. Final Answer:

   -f -> Option B

4. Quick Check:

   Regular file check = -f [OK]

Hint: Remember: -f means file, -d means directory [OK]

Common Mistakes:

• Confusing -f with -d
• Using -e which only checks existence
• Mixing -x (executable) with file type

2. Which of the following is the correct syntax to check if a directory exists in bash?

easy

A. if [ -f /path/to/dir ]; then echo "Exists"; fi

B. if [ -x /path/to/dir ]; then echo "Exists"; fi

C. if [ -e /path/to/dir ]; then echo "Exists"; fi

D. if [ -d /path/to/dir ]; then echo "Exists"; fi

Solution

1. Step 1: Identify the operator for directory check

   -d is used to check if a path is a directory.

2. Step 2: Verify the syntax correctness

   The syntax if [ -d /path/to/dir ]; then ... fi is correct for checking directory existence.

3. Final Answer:

   if [ -d /path/to/dir ]; then echo "Exists"; fi -> Option D

4. Quick Check:

   Directory check uses -d [OK]

Hint: Use -d to check directories, not -f or -x [OK]

Common Mistakes:

• Using -f to check directories
• Confusing -e (exists) with directory check
• Missing spaces inside [ ] causing syntax errors

3. What will be the output of this script if myfile.txt exists and is readable but not writable?

if [ -r myfile.txt ]; then echo "Readable"; else echo "Not readable"; fi
if [ -w myfile.txt ]; then echo "Writable"; else echo "Not writable"; fi

medium

A. Readable\nWritable

B. Not readable\nWritable

C. Readable\nNot writable

D. Not readable\nNot writable

Solution

1. Step 1: Check readability condition

   The file exists and is readable, so [ -r myfile.txt ] is true, printing "Readable".

2. Step 2: Check writability condition

   The file is not writable, so [ -w myfile.txt ] is false, printing "Not writable".

3. Final Answer:

   Readable\nNot writable -> Option C

4. Quick Check:

   Readable true, writable false = A [OK]

Hint: Check each permission separately with -r and -w [OK]

Common Mistakes:

• Assuming writable if readable
• Mixing up -r and -w operators
• Ignoring else branch output

4. Identify the error in this bash snippet that checks if a file exists and is executable:

if [ -e myscript.sh -a -x ]; then echo "Executable file"; fi

medium

A. Missing filename after -x operator

B. Wrong operator -e should be -f

C. Missing spaces around -a operator

D. Should use double brackets [[ ]] instead of single [ ]

Solution

1. Step 1: Analyze the -x operator usage

   The -x operator requires a filename argument, but none is provided after it.

2. Step 2: Check other parts of the condition

   -e myscript.sh is valid to check existence; spaces around -a are correct; using single brackets is valid.

3. Final Answer:

   Missing filename after -x operator -> Option A

4. Quick Check:

   -x needs a file name [OK]

Hint: Always provide filename after each test operator [OK]

Common Mistakes:

• Forgetting filename after -x
• Confusing -e and -f operators
• Missing spaces around operators causing syntax errors

5. You want to write a bash script that prints "Ready" only if config.cfg exists, is a regular file, and is readable and writable. Which condition correctly checks all these?

hard

A. if [ -f config.cfg ] && [ -r config.cfg ] && [ -w config.cfg ]; then echo "Ready"; fi

B. if [ -e config.cfg -a -r config.cfg -a -w config.cfg ]; then echo "Ready"; fi

C. if [ -d config.cfg ] && [ -r config.cfg ] && [ -w config.cfg ]; then echo "Ready"; fi

D. if [ -e config.cfg ] && [ -r config.cfg ] && [ -w config.cfg ]; then echo "Ready"; fi

Solution

1. Step 1: Identify the operator for regular file check

   -f checks if the path is a regular file, which is required.

2. Step 2: Combine all conditions correctly

   Using && between separate [ ] tests is correct and clear. The script checks existence as a file, readability, and writability.

3. Step 3: Eliminate incorrect options

   if [ -e config.cfg ] && [ -r config.cfg ] && [ -w config.cfg ]; then echo "Ready"; fi uses -e which allows directories; if [ -e config.cfg -a -r config.cfg -a -w config.cfg ]; then echo "Ready"; fi uses -e which allows directories; if [ -d config.cfg ] && [ -r config.cfg ] && [ -w config.cfg ]; then echo "Ready"; fi checks for directory which is wrong.

4. Final Answer:

   if [ -f config.cfg ] && [ -r config.cfg ] && [ -w config.cfg ]; then echo "Ready"; fi -> Option A

5. Quick Check:

   Regular file with read/write uses -f, -r, -w combined [OK]

Hint: Use -f for file, combine tests with && for clarity [OK]

Common Mistakes:

• Using -e instead of -f to check file type
• Using -a inside single [ ] causing confusion
• Checking directory instead of file