tr (translate characters) in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this tr command?

Given the input string hello world, what is the output of the command echo 'hello world' | tr 'a-z' 'A-Z'?

Linux CLI

echo 'hello world' | tr 'a-z' 'A-Z'

A hello world

B HELLO WORLD

C HELLO world

D Error: invalid range

💡 Hint

The tr command can convert lowercase letters to uppercase by specifying ranges.

The command translates all lowercase letters (a-z) to their uppercase equivalents (A-Z), so 'hello world' becomes 'HELLO WORLD'.

💻 Command Output

intermediate

What does this tr command output?

What is the output of echo '123-456-7890' | tr -d '-'?

Linux CLI

echo '123-456-7890' | tr -d '-'

A 1234567890

B 123 456 7890

C Error: invalid option

D 123-456-7890

💡 Hint

The -d option deletes characters specified in the set.

The command deletes all dashes '-' from the input, resulting in '1234567890'.

💻 Command Output

advanced

What is the output of this tr command with squeeze?

Given the input echo 'aaabbbcccaaa' | tr -s 'a', what is the output?

Linux CLI

echo 'aaabbbcccaaa' | tr -s 'a'

A abbbccc

B abbbcccaa

C abbbccca

D Error: invalid option

💡 Hint

The -s option squeezes repeated characters in the set into one.

The command squeezes repeated 'a's into a single 'a', so 'aaabbbcccaaa' becomes 'abbbccca'.

💻 Command Output

advanced

What error does this tr command produce?

What error message results from running echo 'test' | tr 'a-z' 'A-Z' '0-9'?

Linux CLI

echo 'test' | tr 'a-z' 'A-Z' '0-9'

A tr: extra operand '0-9'

B test

C TEST

D Error: invalid range

💡 Hint

The tr command accepts only two sets of characters for translation.

The command provides three arguments to tr, which expects only two sets. This causes an error about an extra operand.

🚀 Application

expert

How many characters are in the output after this tr command?

Given the input string echo 'aabbccddeeff' | tr -d 'bdf', how many characters does the output contain?

Linux CLI

echo 'aabbccddeeff' | tr -d 'bdf'

A 8

B 9

C 12

D 6

💡 Hint

Count the characters after deleting all 'b', 'd', and 'f'.

The input has 12 characters: a a b b c c d d e e f f. Deleting 'b', 'd', and 'f' removes 2 b's, 2 d's, and 2 f's (6 total). Remaining characters: a a c c e e (6 characters). So output length is 6.

Practice

1. What does the tr command do in Linux?

easy

A. It translates or deletes characters from input text.

B. It lists files in a directory.

C. It compiles source code.

D. It displays the current directory path.

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 A, C, and D describe other commands like ls, compilers, and pwd, which are unrelated to tr.

3. Final Answer:

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

4. Quick Check:

   tr = translate/delete chars [OK]

Hint: Remember: tr = translate characters [OK]

Common Mistakes:

• Confusing tr with ls or pwd commands
• Thinking tr compiles code
• Assuming tr lists files

2. Which of the following is the correct syntax to replace all lowercase 'a' characters with 'b' using tr?

easy

A. tr -replace a b

B. tr a-z b

C. tr 'a' 'b'

D. tr 'a' to 'b'

Solution

1. Step 1: Recall tr syntax

   The correct syntax uses single quotes around the sets of characters: tr 'a' 'b'.

2. Step 2: Evaluate options

   tr a-z b uses a range which translates all lowercase letters to 'b' (padded), incorrect for only 'a'. Options A and C use invalid syntax for tr.

3. Final Answer:

   tr 'a' 'b' -> Option C

4. Quick Check:

   Use quotes around sets in tr [OK]

Hint: Use quotes around characters in tr command [OK]

Common Mistakes:

• Using range 'a-z' for single character
• Using invalid options like -replace
• Adding extra words like 'to'

3. What is the output of the command:
echo "hello world" | tr 'a-z' 'A-Z'?

medium

A. HELLO WORLD

B. hello world

C. HELLO world

D. Error: invalid range

Solution

1. Step 1: Understand the command

   The command converts all lowercase letters (a-z) to uppercase (A-Z) in the input text "hello world".

2. Step 2: Apply translation

   All letters become uppercase, so "hello world" becomes "HELLO WORLD".

3. Final Answer:

   HELLO WORLD -> Option A

4. Quick Check:

   Lowercase to uppercase translation = HELLO WORLD [OK]

Hint: tr 'a-z' 'A-Z' converts lowercase to uppercase [OK]

Common Mistakes:

• Expecting partial uppercase
• Confusing input and output
• Thinking it causes an error

4. Identify the error in this command:
echo "123abc" | tr '0-9' 'a-j'

medium

A. Ranges in sets are mismatched length causing error

B. No error, command works correctly

C. Output will be empty

D. Quotes are missing around sets

Solution

1. Step 1: Analyze the command

   The command replaces digits 0-9 with letters a-j. Both sets have equal length (10 characters).

2. Step 2: Check for syntax or runtime errors

   Quotes are present, ranges are valid and equal length, so no error occurs.

3. Final Answer:

   No error, command works correctly -> Option B

4. Quick Check:

   Equal length ranges with quotes = valid command [OK]

Hint: Ensure equal length sets in tr to avoid errors [OK]

Common Mistakes:

• Assuming mismatched lengths cause errors here
• Missing quotes around sets
• Expecting output to be empty

5. You want to remove all vowels (a, e, i, o, u) from a text file named input.txt. Which command correctly does this using tr?

hard

A. tr -remove 'aeiou' < input.txt

B. tr 'aeiou' < input.txt

C. tr -r 'aeiou' < input.txt

D. tr -d 'aeiou' < input.txt

Solution

1. Step 1: Understand the goal

   The goal is to delete vowels from the input text file.

2. Step 2: Identify correct tr option

   The -d option deletes specified characters. So tr -d 'aeiou' removes vowels.

3. Step 3: Check other options

   tr 'aeiou' < input.txt lacks the second character set, causing an error. Options C and D use invalid options.

4. Final Answer:

   tr -d 'aeiou' < input.txt -> Option D

5. Quick Check:

   Use -d to delete chars in tr [OK]

Hint: Use tr -d to delete characters from input [OK]

Common Mistakes:

• Missing second character set operand
• Using invalid options like -r or -remove
• Forgetting to redirect input