File existence checks in Bash Scripting - Mini Project: Build & Apply

File existence checks

📖 Scenario: You are writing a simple script to check if certain files exist on your computer. This is useful when you want to make sure important files are present before running other commands.

🎯 Goal: Create a bash script that checks if a file named data.txt exists in the current folder and prints a message based on the result.

📋 What You'll Learn

Create a variable called filename with the value data.txt

Create a variable called filepath that stores the full path to the file using $(pwd) and filename

Use an if statement with the -e test to check if the file exists at filepath

Print File exists. if the file is found

Print File does not exist. if the file is not found

💡 Why This Matters

🌍 Real World

Checking if files exist is a common task in automation scripts to avoid errors when processing files.

💼 Career

Many IT and DevOps roles require writing scripts that verify file presence before running backups, deployments, or data processing.

1

Create the filename variable

Create a variable called filename and set it to the string data.txt.

Bash Scripting

# Create a variable called filename and set it to 'data.txt'
# Your code here

Hint

Use filename="data.txt" to create the variable.

2

Create the filepath variable

Create a variable called filepath that combines the current directory path from $(pwd) and the filename variable, separated by a slash /.

Bash Scripting

filename="data.txt"
# Create a variable called filepath combining $(pwd) and filename
# Your code here

Hint

Use filepath="$(pwd)/$filename" to combine the current directory and filename.

3

Check if the file exists

Write an if statement that uses [ -e "$filepath" ] to check if the file exists at filepath. Inside the if, print File exists.. Use else to print File does not exist. if the file is missing.

Bash Scripting

filename="data.txt"
filepath="$(pwd)/$filename"
# Write an if statement to check if the file exists at filepath
# Print 'File exists.' if true, else print 'File does not exist.'
# Your code here

Hint

Use if [ -e "$filepath" ]; then to check file existence.

4

Print the result

Run the script and ensure it prints File exists. if data.txt is in the current folder, or File does not exist. if it is not.

Bash Scripting

filename="data.txt"
filepath="$(pwd)/$filename"
if [ -e "$filepath" ]; then
    echo "File exists."
else
    echo "File does not exist."
fi
# Run the script to see the output

Hint

Make sure the file data.txt is in your current folder or not, then run the script.

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