tr for character transformation in Bash Scripting - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to convert all lowercase letters in the input to uppercase using tr.

Bash Scripting

echo "hello world" | tr [1]

Drag options to blanks, or click blank then click option'

A"a-z A-Z"

B"a-z" "A-Z"

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to quote the character sets.

Swapping the order of character sets.

The tr command uses the syntax tr 'a-z' 'A-Z' to convert lowercase letters to uppercase.

2fill in blank

medium

Complete the code to replace all spaces with underscores using tr.

Bash Scripting

echo "hello world" | tr [1]

Drag options to blanks, or click blank then click option'

A" _"

C" " "_"

Attempts:

3 left

💡 Hint

Common Mistakes

Not quoting the space character.

Using the wrong order of characters.

The tr command replaces characters from the first set with those in the second set. Here, spaces are replaced with underscores.

3fill in blank

hard

Fix the error in the code to delete all digits from the input using tr.

Bash Scripting

echo "abc123def" | tr -d [1]

Drag options to blanks, or click blank then click option'

A"0-9"

B"a-z"

C"A-Z"

D"1-9"

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect character ranges like 1-9 which misses zero.

Trying to delete letters instead of digits.

The -d option deletes characters. To delete digits, use the range 0-9.

4fill in blank

hard

Fill both blanks to replace all vowels with the letter 'x' using tr.

Bash Scripting

echo "hello world" | tr [1] [2]

Drag options to blanks, or click blank then click option'

A"aeiou"

B"xyz"

C"x"

D"aeiouAEIOU"

Attempts:

3 left

💡 Hint

Common Mistakes

Not including uppercase vowels.

Using multiple characters in the replacement set.

To replace vowels (both lowercase and uppercase) with 'x', use tr 'aeiouAEIOU' 'x'.

5fill in blank

hard

Fill all three blanks to create a dictionary that maps each word to its length, but only for words longer than 3 characters.

Bash Scripting

words=("apple" "bat" "cat" "dog" "elephant")
for word in "${words[@]}"; do
  if [[ ${#word} [1] [2] ]]; then
    echo "${word}: $[3]"
  fi
done

Drag options to blanks, or click blank then click option'

A>

B3

C${#word}

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using less than instead of greater than.

Printing the word instead of its length.

The code checks if the length of the word is greater than 3, then prints the word and its length.

Practice

1. What does the tr command do in bash scripting?

easy

A. It transforms or deletes characters from input text streams.

B. It compiles bash scripts into executables.

C. It lists files in a directory.

D. It runs commands in the background.

Solution

1. Step 1: Understand the purpose of tr

   The tr command is used to translate or delete characters from input text streams.

2. Step 2: Compare with other options

   Options B, C, and D describe unrelated commands or functions in bash.

3. Final Answer:

   It transforms or deletes characters from input text streams. -> Option A

4. Quick Check:

   tr = transform/delete characters [OK]

Hint: Remember: tr means translate characters [OK]

Common Mistakes:

• Confusing tr with file listing commands like ls
• Thinking tr compiles scripts
• Assuming tr runs commands in background

2. Which of the following is the correct syntax to convert lowercase letters to uppercase using tr?

easy

A. echo "hello" | tr 'A-Z' '0-9'

B. echo "hello" | tr 'a-z' 'A-Z'

C. echo "hello" | tr '0-9' 'A-Z'

D. echo "hello" | tr 'A-Z' 'a-z'

Solution

1. Step 1: Identify the correct character ranges for case conversion

   To convert lowercase to uppercase, use 'a-z' as source and 'A-Z' as target.

2. Step 2: Check the syntax correctness

   echo "hello" | tr 'a-z' 'A-Z' correctly uses tr 'a-z' 'A-Z'. Other options either reverse case or use wrong ranges.

3. Final Answer:

   echo "hello" | tr 'a-z' 'A-Z' -> Option B

4. Quick Check:

   Lowercase to uppercase = echo "hello" | tr 'a-z' 'A-Z' [OK]

Hint: Use 'a-z' then 'A-Z' to uppercase letters [OK]

Common Mistakes:

• Swapping source and target ranges
• Using digits instead of letters
• Mixing uppercase and lowercase incorrectly

3. What is the output of this command?

echo "Hello World 123" | tr -d '0-9'

medium

A. Hello World 123

B. HelloWorld123

C. HelloWorld

D. Hello World

Solution

1. Step 1: Understand the -d option in tr

   The -d option deletes characters matching the set given, here digits '0-9'.

2. Step 2: Apply deletion to the input string

   All digits '1', '2', '3' are removed, leaving "Hello World " with spaces intact.

3. Final Answer:

   Hello World -> Option D

4. Quick Check:

   Digits deleted = "Hello World " [OK]

Hint: Use -d to delete characters, here digits removed [OK]

Common Mistakes:

• Expecting digits to be replaced, not deleted
• Removing spaces accidentally
• Confusing -d with character translation

4. Identify the error in this command:

echo "abc123" | tr 'a-z' 'A-Z' -d '0-9'

medium

A. The command will convert letters but ignore digits.

B. The order of options is wrong; -d must come before sets.

C. You cannot combine translation and deletion in one tr command.

D. The syntax is correct and will work as expected.

Solution

1. Step 1: Understand tr option usage

   tr does not support combining translation and deletion in one command; they are separate operations.

2. Step 2: Analyze the command

   The command tries to translate and delete simultaneously, which is invalid syntax.

3. Final Answer:

   You cannot combine translation and deletion in one tr command. -> Option C

4. Quick Check:

   Translation + deletion together = invalid [OK]

Hint: tr does either translate OR delete, not both at once [OK]

Common Mistakes:

• Trying to chain translate and delete in one tr call
• Assuming option order fixes the problem
• Expecting partial command success

5. You want to replace all vowels in a string with the character '*', but keep other characters unchanged. Which command achieves this?

hard

A. echo "banana" | tr 'aeiou' '*'

B. echo "banana" | tr 'aeiou' 'AEIOU'

C. echo "banana" | tr -d 'aeiou'

D. echo "banana" | tr 'aeiou' 'ABCDE'

Solution

1. Step 1: Understand character replacement with tr

   To replace vowels with '*', map all vowels to a single character '*'.

2. Step 2: Analyze each option

   echo "banana" | tr 'aeiou' '*' replaces each vowel with '*'. echo "banana" | tr 'aeiou' 'AEIOU' changes vowels to uppercase vowels. echo "banana" | tr -d 'aeiou' deletes vowels. echo "banana" | tr 'aeiou' 'ABCDE' replaces vowels with A,B,C,D,E respectively.

3. Final Answer:

   echo "banana" | tr 'aeiou' '*' -> Option A

4. Quick Check:

   Vowels replaced by '*' = echo "banana" | tr 'aeiou' '*' [OK]

Hint: Map vowels to '*' with single char target in tr [OK]

Common Mistakes:

• Using a target set like 'ABCDE' instead of '*'
• Deleting vowels instead of replacing
• Replacing vowels with uppercase instead of '*'