File existence checks in Bash Scripting - Cheat Sheet & Quick Revision

Recall & Review

beginner

What command checks if a file exists in a bash script?

Use the test command with -e flag: if [ -e filename ]; then checks if the file named 'filename' exists.

beginner

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

The -f flag checks if the file exists and is a regular file (not a directory or special file).

beginner

How do you check if a directory exists in bash?

Use -d flag: if [ -d directoryname ]; then checks if 'directoryname' exists and is a directory.

intermediate

What is the difference between -e and -f in bash file tests?

-e checks if a file or directory exists. -f checks if a regular file exists (not directory).

beginner

Write a simple bash script snippet that prints 'File found' if a file named 'data.txt' exists.

if [ -e data.txt ]; then
  echo "File found"
else
  echo "File not found"
fi

Which bash test flag checks if a file exists regardless of type?

A -f

B -e

C -d

D -x

The -e flag checks if a file or directory exists, regardless of type.

What does the -d flag check in bash?

A If a file is executable

B If a regular file exists

C If a directory exists

D If a file is empty

The -d flag checks if the given path exists and is a directory.

What will this script print if 'myfile' does not exist?

if [ -f myfile ]; then echo "Found"; else echo "Not found"; fi

A Found

B Nothing

C Error

D Not found

Since 'myfile' does not exist, the condition fails and 'Not found' is printed.

Which test flag would you use to check if a file is executable?

A -x

B -r

C -w

D -e

The -x flag checks if the file is executable.

What does this script check?

if [ -e /tmp ]; then echo "Exists"; fi

A If /tmp exists (file or directory)

B If /tmp is a directory

C If /tmp is a regular file

D If /tmp is executable

The -e flag checks if the path exists, whether file or directory.

Explain how to check if a file exists in a bash script and what flags you can use for different file types.

Think about the test command and its flags.

Write a bash script snippet that checks if a directory named 'backup' exists and prints a message accordingly.

Use the -d flag inside an if condition.

Practice

1. Which command correctly checks if a file named data.txt exists in a bash script?

easy

A. if [ -e data.txt ]; then echo "File exists"; fi

B. if ( -e data.txt ); then echo "File exists"; fi

C. if [[ exists data.txt ]]; then echo "File exists"; fi

D. if test -f data.txt then echo "File exists"; fi

Solution

1. Step 1: Understand the correct syntax for file existence check

   The test command with square brackets and -e checks if a file or directory exists.

2. Step 2: Verify the command structure

   The command if [ -e data.txt ]; then ... fi is the correct syntax in bash for this check.

3. Final Answer:

   if [ -e data.txt ]; then echo "File exists"; fi -> Option A

4. Quick Check:

   Use [ -e filename ] to check existence [OK]

Hint: Use [ -e filename ] inside if for existence check [OK]

Common Mistakes:

• Using parentheses instead of square brackets
• Using incorrect test operators like 'exists'
• Missing semicolon or then keyword

2. Which of the following is the correct syntax to check if a file report.log exists and is a regular file in bash?

easy

A. if [ -d report.log ]; then echo "Exists"; fi

B. if [ -f report.log ]; then echo "Exists"; fi

C. if [ -e report.log ]; then echo "Exists"; fi

D. if test -x report.log; then echo "Exists"; fi

Solution

1. Step 1: Identify the test for regular file

   The -f option checks if the file exists and is a regular file (not directory).

2. Step 2: Confirm the syntax

   The syntax if [ -f report.log ]; then ... fi correctly checks for a regular file.

3. Final Answer:

   if [ -f report.log ]; then echo "Exists"; fi -> Option B

4. Quick Check:

   -f checks regular file existence [OK]

Hint: Use [ -f filename ] to check regular file existence [OK]

Common Mistakes:

• Using -d which checks for directories
• Using -x which checks for executable permission
• Confusing -e (exists) with -f (regular file)

3. What will be the output of this script if myfile.txt does not exist?

if [ -e myfile.txt ]; then
  echo "Found"
else
  echo "Not Found"
fi

medium

A. Not Found

B. Syntax error

C. Found

D. No output

Solution

1. Step 1: Understand the condition

   The condition [ -e myfile.txt ] checks if the file exists.

2. Step 2: Evaluate the file existence

   Since myfile.txt does not exist, the condition is false, so the else branch runs.

3. Final Answer:

   Not Found -> Option A

4. Quick Check:

   File missing triggers else branch [OK]

Hint: If file missing, else branch runs [OK]

Common Mistakes:

• Assuming output is 'Found' even if file missing
• Confusing -e with other test operators
• Missing else branch handling

4. Identify the error in this bash snippet that checks if config.cfg exists:

if [ -e config.cfg ]
  echo "Exists"
fi

medium

A. Echo command syntax is wrong

B. Wrong test operator -e used

C. Missing closing bracket ]

D. Missing then keyword after condition

Solution

1. Step 1: Check if statement syntax

   Bash requires the then keyword after the condition in an if statement.

2. Step 2: Identify missing part

   The snippet lacks then after [ -e config.cfg ], causing a syntax error.

3. Final Answer:

   Missing then keyword after condition -> Option D

4. Quick Check:

   if needs then after condition [OK]

Hint: Always put then after if condition [OK]

Common Mistakes:

• Omitting then keyword
• Forgetting semicolon before then on same line
• Misplacing brackets

5. You want to write a bash script that checks if a file named backup.tar.gz exists, and if it does, prints "Backup found", otherwise creates an empty file with that name. Which script snippet correctly does this?

hard

A. if [ -e backup.tar.gz ]; then touch backup.tar.gz; else echo "Backup found"; fi

B. if [ -f backup.tar.gz ]; then touch backup.tar.gz; else echo "Backup found"; fi

C. if [ -e "backup.tar.gz" ]; then echo "Backup found"; else touch backup.tar.gz; fi

D. if test -d backup.tar.gz; then echo "Backup found"; else touch backup.tar.gz; fi

Solution

1. Step 1: Check file existence correctly

   Use [ -e "backup.tar.gz" ] to check if the file exists, quoting filename to handle spaces.

2. Step 2: Execute correct commands based on condition

   If file exists, print "Backup found"; else create empty file with touch.

3. Final Answer:

   if [ -e "backup.tar.gz" ]; then echo "Backup found"; else touch backup.tar.gz; fi -> Option C

4. Quick Check:

   Check existence then else create file [OK]

Hint: Quote filenames and use if-else for existence and creation [OK]

Common Mistakes:

• Swapping then and else commands
• Using -d to check regular files
• Not quoting filenames with spaces