tr for character transformation in Bash Scripting - Mini Project: Build & Apply

Character Transformation Using tr Command

📖 Scenario: You work in a small office where you often receive text files with inconsistent letter cases. Your task is to automate the process of converting all lowercase letters to uppercase to maintain uniformity in reports.

🎯 Goal: Build a simple Bash script that uses the tr command to convert lowercase letters in a given string to uppercase.

📋 What You'll Learn

Create a variable called input_text with the exact value hello world

Create a variable called uppercase_text that uses tr to convert input_text from lowercase to uppercase

Print the value of uppercase_text

💡 Why This Matters

🌍 Real World

Automating text formatting tasks like converting letter cases in reports or filenames.

💼 Career

Shell scripting skills are essential for system administrators and developers to automate repetitive text processing tasks efficiently.

1

DATA SETUP: Create the input text variable

Create a variable called input_text and set it to the string hello world exactly.

Bash Scripting

# Create a variable called input_text with the value 'hello world'
# Your code here

Hint

Use input_text="hello world" to assign the string.

2

CONFIGURATION: Prepare to transform characters

Create a variable called uppercase_text that uses the tr command to convert all lowercase letters in input_text to uppercase.

Bash Scripting

input_text="hello world"
# Use tr to convert input_text to uppercase and store in uppercase_text
# Your code here

Hint

Use $(echo "$input_text" | tr '[:lower:]' '[:upper:]') to convert lowercase to uppercase.

3

CORE LOGIC: Apply the character transformation

Use the tr command inside a command substitution to convert input_text to uppercase and assign it to uppercase_text.

Bash Scripting

input_text="hello world"
uppercase_text=$(echo "$input_text" | tr '[:lower:]' '[:upper:]')
# Your code here

Hint

This step repeats the transformation to reinforce the core logic.

4

OUTPUT: Display the transformed text

Print the value of uppercase_text to show the converted uppercase string.

Bash Scripting

input_text="hello world"
uppercase_text=$(echo "$input_text" | tr '[:lower:]' '[:upper:]')
# Print uppercase_text
# Your code here

Hint

Use echo "$uppercase_text" to print the result.

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 '*'