tr for character transformation in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of tr command with character deletion

What is the output of this command?

echo "hello world" | tr -d 'aeiou'

Bash Scripting

echo "hello world" | tr -d 'aeiou'

A hll wrld

B hello world

C h e l l o w o r l d

D Syntax error

💡 Hint

The -d option deletes characters specified.

The command deletes all vowels from the input string, leaving only consonants and spaces.

💻 Command Output

intermediate

Transform lowercase to uppercase using tr

What is the output of this command?

echo "bash scripting" | tr 'a-z' 'A-Z'

Bash Scripting

echo "bash scripting" | tr 'a-z' 'A-Z'

A BASH SCRIPTING

B bash scripting

C Bash Scripting

D Syntax error

💡 Hint

tr replaces characters from the first set with the second set.

All lowercase letters are converted to uppercase letters.

💻 Command Output

advanced

Output of tr with complement and squeeze

What is the output of this command?

echo "aaabbbccc111222333" | tr -cs 'a-z' $'\n'

Bash Scripting

echo "aaabbbccc111222333" | tr -cs 'a-z' $'\n'

A aaa bbb ccc

B

aaa
bbb
ccc

C aaabbbccc

D Syntax error

💡 Hint

The -c option complements the set; -s squeezes repeated characters.

The command replaces all characters except lowercase letters with newlines and squeezes repeats, resulting in each group of letters on a new line.

💻 Command Output

advanced

Effect of tr with overlapping sets

What is the output of this command?

echo "123abc" | tr '1-3a-c' 'x-z1-3'

Bash Scripting

echo "123abc" | tr '1-3a-c' 'x-z1-3'

A 123abc

B Syntax error

C xyz123

D xxx111

💡 Hint

Characters in the first set are replaced by corresponding characters in the second set.

Digits 1-3 map to x-z and letters a-c map to 1-3, so '123abc' becomes 'xyz123'.

💻 Command Output

expert

Count unique characters after tr transformation

What is the number of unique characters in the output of this command?

echo "Hello World! 123" | tr 'A-Za-z' 'n-za-mN-ZA-M' | tr -d ' ' | tr -d '!' | fold -w1 | sort -u | wc -l

Bash Scripting

echo "Hello World! 123" | tr 'A-Za-z' 'n-za-mN-ZA-M' | tr -d ' ' | tr -d '!' | fold -w1 | sort -u | wc -l

A 12

B 15

C 13

D 10

💡 Hint

The first tr applies ROT13 cipher, then spaces and '!' are removed, unique characters counted.

ROT13 transforms letters, digits remain unchanged. After removing spaces and '!', counting unique characters yields 10.

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 '*'