File test operators (-f, -d, -e, -r, -w, -x) in Bash Scripting - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the -f file test operator check in a bash script?

The -f operator checks if a given path is a regular file (not a directory or special file).

beginner

How do you test if a directory exists using bash file test operators?

Use the -d operator to check if a directory exists at the given path.

intermediate

What is the difference between -e and -f operators?

-e checks if a file or directory exists (any type), while -f checks specifically for a regular file.

beginner

Which file test operator checks if a file is readable?

The -r operator checks if the current user has read permission on the file.

beginner

Explain what -w and -x operators check in bash.

-w checks if the file is writable, and -x checks if the file is executable by the current user.

Which operator would you use to check if a file exists regardless of type?

A -d

B -f

C -e

D -r

The -e operator checks if any file or directory exists at the path.

What does the -d operator test for?

A If a directory exists

B If a regular file exists

C If a file is readable

D If a file is executable

-d tests if the path is a directory.

If you want to check if a file can be executed, which operator do you use?

A -r

B -w

C -f

D -x

-x checks if the file is executable.

Which operator would confirm a file is writable?

A -r

B -w

C -e

D -d

-w checks write permission on the file.

What does -f specifically check?

A File is a regular file

B File is a directory

C File exists (any type)

D File is executable

-f checks if the file is a regular file.

Describe how you would check if a file exists and is readable in a bash script using file test operators.

Think about testing existence first, then readability.

Explain the difference between checking if a path is a directory versus a regular file using bash file test operators.

Directories and files behave differently in scripts.

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