Looping over files and directories in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this script when run in a directory with files a.txt, b.txt, and c.log?

Consider this bash script:

for file in *.txt; do echo "$file"; done

What will it print?

Bash Scripting

for file in *.txt; do echo "$file"; done

A *.txt

B

a.txt
b.txt

C

a.txt
b.txt
c.log

D

a.txt
b.txt
*.txt

💡 Hint

The wildcard *.txt matches only files ending with .txt.

The loop iterates over files matching the pattern *.txt, so it prints only a.txt and b.txt, not c.log or the literal '*.txt'.

💻 Command Output

intermediate

What does this script output if the directory contains subdirectories dir1 and dir2?

Given this script:

for entry in *; do if [ -d "$entry" ]; then echo "$entry"; fi; done

What will it print?

Bash Scripting

for entry in *; do if [ -d "$entry" ]; then echo "$entry"; fi; done

A

dir1
dir2

B

dir1
dir2
file.txt

C *.txt

D file.txt

💡 Hint

The test -d checks if the entry is a directory.

The loop lists all entries, but only prints those that are directories, so it prints dir1 and dir2 only.

📝 Syntax

advanced

Which option correctly loops over all .log files and prints their names?

Choose the correct bash loop syntax to print all .log files in the current directory.

A for file in *.log; do echo $file; done

B for file in *.log { echo $file; }

C for (file in *.log); do echo $file; done

D foreach file in *.log; do echo $file; done

💡 Hint

Bash uses 'for var in list; do ... done' syntax.

Option A uses correct bash syntax. Options B, C, and D use invalid syntax causing errors.

🚀 Application

advanced

How to count the number of files (not directories) in the current directory using a loop?

You want to count files only (exclude directories). Which script correctly does this?

A

count=0
for item in *; do count=$((count+1)); done
echo $count

B

count=0
for item in *; do if [ -d "$item" ]; then count=$((count+1)); fi; done
echo $count

C

count=0
for item in *; do if [ -f "$item" ]; then count=$((count+1)); fi; done
echo $count

D

count=0
for item in *; do if [ -e "$item" ]; then count=$((count+1)); fi; done
echo $count

💡 Hint

Use -f to test if an entry is a regular file.

Option C counts only files. B counts directories, C counts all entries, D counts all existing entries including directories.

🔧 Debug

expert

Why does this script fail to print filenames with spaces correctly?

Script:

for file in $(ls *.txt); do echo "$file"; done

What is the problem?

Bash Scripting

for file in $(ls *.txt); do echo "$file"; done

A It loops over directories instead of files

B It does not expand *.txt pattern

C It causes a syntax error due to missing quotes

D It splits filenames on spaces, so multi-word names break into parts

💡 Hint

Command substitution splits output by spaces and newlines.

Using $(ls *.txt) splits filenames on spaces, breaking names with spaces into multiple words. Using 'for file in *.txt' is safer.

Practice

1. What does the following bash loop do?
for file in *; do echo "$file"; done

easy

A. It runs the echo command once without any output.

B. It deletes all files in the current folder.

C. It lists only directories in the current folder.

D. It prints the names of all files and directories in the current folder.

Solution

1. Step 1: Understand the loop variable and pattern

   The loop uses * which matches all files and directories in the current folder.

2. Step 2: Analyze the command inside the loop

   Each matched item is stored in file and printed with echo.

3. Final Answer:

   It prints the names of all files and directories in the current folder. -> Option D

4. Quick Check:

   Loop over * prints all names [OK]

Hint: Remember * matches all files and folders [OK]

Common Mistakes:

• Thinking * matches only files, not directories
• Assuming the loop deletes files
• Believing echo runs only once

2. Which of the following is the correct syntax to loop over all directories only in the current folder?

easy

A. for dir in *; do if [ -f "$dir" ]; then echo "$dir"; fi; done

B. for dir in *; do echo "$dir"; done

C. for dir in */; do echo "$dir"; done

D. for dir in /*; do echo "$dir"; done

Solution

1. Step 1: Understand the pattern for directories

   The pattern */ matches only directories in the current folder because directories end with a slash.

2. Step 2: Check the loop and echo command

   The loop iterates over directories and prints their names correctly.

3. Final Answer:

   for dir in */; do echo "$dir"; done -> Option C

4. Quick Check:

   */ matches directories only [OK]

Hint: Use */ pattern to match directories only [OK]

Common Mistakes:

• Using * matches files and directories, not only directories
• Using -f to check for directories instead of -d
• Using absolute path /* instead of current folder

3. What will be the output of this script if the current folder contains files: file1.txt, file2.txt and a directory docs/?

for item in *; do
  if [ -f "$item" ]; then
    echo "File: $item"
  else
    echo "Not a file: $item"
  fi
done

medium

A. File: file1.txt
File: file2.txt
Not a file: docs

B. File: file1.txt
File: file2.txt
File: docs

C. Not a file: file1.txt
Not a file: file2.txt
Not a file: docs

D. File: file1.txt
Not a file: file2.txt
Not a file: docs

Solution

1. Step 1: Identify file and directory checks

   The script uses [ -f "$item" ] to check if the item is a file.

2. Step 2: Apply checks to each item

   file1.txt and file2.txt are files, so print "File: ..."; docs is a directory, so print "Not a file: docs".

3. Final Answer:

   File: file1.txt File: file2.txt Not a file: docs -> Option A

4. Quick Check:

   -f true for files only [OK]

Hint: Use -f to test files, else it's not a file [OK]

Common Mistakes:

• Assuming directories pass -f test
• Confusing -f with -d
• Expecting directory names with trailing slash

4. Find the error in this script that tries to print only directories:

for item in *; do
  if [ -f "$item" ]; then
    echo "$item"
  fi
done

medium

A. The echo command is missing quotes around $item.

B. It uses -f to check files instead of -d for directories.

C. The loop pattern * does not match any files.

D. The script will print directories correctly.

Solution

1. Step 1: Understand the test used

   The script uses [ -f "$item" ] which checks if the item is a file, not a directory.

2. Step 2: Identify correct test for directories

   To check directories, [ -d "$item" ] should be used instead.

3. Final Answer:

   It uses -f to check files instead of -d for directories. -> Option B

4. Quick Check:

   Use -d to test directories [OK]

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

Common Mistakes:

• Confusing -f and -d tests
• Assuming * matches only directories
• Ignoring quotes around variables

5. You want to count how many files (not directories) are in the current folder using a bash loop. Which script correctly does this?

hard

A. count=0
for item in *; do
if [ -f "$item" ]; then
count=$((count + 1))
fi
done
echo $count

B. count=0
for item in */; do
count=$((count + 1))
done
echo $count

C. count=0
for item in *; do
if [ -d "$item" ]; then
count=$((count + 1))
fi
done
echo $count

D. count=0
for item in *; do
count=$((count + 1))
done
echo $count

Solution

1. Step 1: Understand the goal

   We want to count files only, so we must check each item with [ -f "$item" ].

2. Step 2: Check each option

   count=0 for item in *; do if [ -f "$item" ]; then count=$((count + 1)) fi done echo $count correctly loops over all items, increments count only if item is a file, then prints count.

3. Final Answer:

   count=0 for item in *; do if [ -f "$item" ]; then count=$((count + 1)) fi done echo $count -> Option A

4. Quick Check:

   Use -f test and increment count [OK]

Hint: Increment count only if -f test passes [OK]

Common Mistakes:

• Counting directories instead of files
• Counting all items without checks
• Using */ pattern which matches directories only