String suffix removal (${var%pattern}) in Bash Scripting - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to remove the shortest suffix matching '.txt' from the variable.

Bash Scripting

filename="document.txt"
result=${filename[1]

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

A%'.txt'

B%%'.txt'

C#'.txt'

D##'.txt'

Attempts:

3 left

💡 Hint

Common Mistakes

Using # or ## which remove prefixes instead of suffixes.

Using %% which removes the longest suffix, not the shortest.

The single % removes the shortest matching suffix pattern from the variable's value.

2fill in blank

medium

Complete the code to remove the shortest suffix matching any characters after the last dot.

Bash Scripting

filename="archive.tar.gz"
result=${filename[1]

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

A%.*

B##.*

C#.*

D%%.*

Attempts:

3 left

💡 Hint

Common Mistakes

Using %% which removes the longest suffix, removing more than intended.

Using # or ## which remove prefixes, not suffixes.

Using %.* removes the shortest suffix starting with a dot, effectively removing the file extension.

3fill in blank

hard

Fix the error in the code to correctly remove the shortest suffix '.backup' from the variable.

Bash Scripting

file="data.backup"
clean=${file[1]

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

A##.backup

B#.backup

C%%.backup

D%.backup

Attempts:

3 left

💡 Hint

Common Mistakes

Using # or ## which remove prefixes instead of suffixes.

Using %% which removes longest suffix unnecessarily.

Single % removes the shortest suffix '.backup' correctly; %% removes longest suffix which is unnecessary here.

4fill in blank

hard

Fill both blanks to remove the shortest suffix '.log' and then the longest suffix starting with a dot.

Bash Scripting

file="server.old.log"
step1=${file[1]
result=${step1[2]

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

A%'.log'

B%%'.log'

C%%.*

D%.*

Attempts:

3 left

💡 Hint

Common Mistakes

Using %% first removes too much.

Using %.* first removes shortest suffix starting with dot, not '.log'.

First remove shortest suffix '.log' with %, then remove longest suffix starting with dot with %%.

5fill in blank

hard

Fill all three blanks to create a dictionary with keys as filenames without extensions and values as original filenames, filtering only files ending with '.txt'.

Bash Scripting

files=("a.txt" "b.log" "c.txt")
result=([1]: [2] for f in files if [[ f [3] *.txt ]])

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

A${f%.*}

Bf

C==

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using != instead of == in condition.

Using # or ## instead of % for suffix removal.

Use ${f%.*} to remove extension for key, f as value, and f == *.txt to filter files ending with '.txt'.

Practice

1. What does the Bash expression ${filename%.txt} do to the variable filename?

easy

A. Removes the shortest prefix matching '.txt' from the start of filename

B. Removes the longest suffix matching '.txt' from the end of filename

C. Removes the shortest suffix matching '.txt' from the end of filename

D. Removes the longest prefix matching '.txt' from the start of filename

Solution

1. Step 1: Understand the % operator in Bash

   The single % operator removes the shortest matching suffix pattern from the variable's value.

2. Step 2: Apply to the pattern '.txt'

   It removes '.txt' only if it appears at the end of the string, trimming that suffix.

3. Final Answer:

   Removes the shortest suffix matching '.txt' from the end of filename -> Option C

4. Quick Check:

   ${var%pattern} removes shortest suffix [OK]

Hint: Single % removes shortest suffix, double %% removes longest [OK]

Common Mistakes:

• Confusing % with prefix removal operators
• Using %% instead of %
• Thinking it removes prefix instead of suffix

2. Which of the following is the correct syntax to remove the shortest suffix '.log' from the variable file in Bash?

easy

A. ${file%%.log}

B. ${file%.log}

C. ${file#log}

D. ${file%log}

Solution

1. Step 1: Identify suffix removal syntax

   To remove the shortest suffix matching a pattern, use single % with the pattern including the dot: %.log

2. Step 2: Check each option

   A uses %% which removes longest suffix, C uses # which removes prefix, D misses the dot before 'log'. Only B is correct syntax.

3. Final Answer:

   ${file%.log} -> Option B

4. Quick Check:

   Use single % with pattern for shortest suffix removal [OK]

Hint: Use single % with exact suffix pattern to remove shortest suffix [OK]

Common Mistakes:

• Using %% instead of %
• Confusing % with # for prefix removal
• Omitting the dot in the pattern

3. Given the Bash code:

filename="report.final.txt"
echo ${filename%.txt}

What is the output?

medium

A. report.final.tx

B. report

C. report.final.txt

D. report.final

Solution

1. Step 1: Understand the variable value

   The variable filename contains 'report.final.txt'.

2. Step 2: Apply ${filename%.txt}

   This removes the shortest suffix matching '.txt' from the end, leaving 'report.final'.

3. Final Answer:

   report.final -> Option D

4. Quick Check:

   Suffix '.txt' removed once from end [OK]

Hint: Remove suffix by matching pattern at string end with % [OK]

Common Mistakes:

• Removing more than '.txt' suffix
• Confusing prefix removal with suffix removal
• Expecting the full string unchanged

4. Consider this Bash snippet:

file="archive.tar.gz"
echo ${file%*.gz}

It outputs archive.tar. You want to remove the entire suffix .tar.gz. What is the fix?

medium

A. Use ${file%%*.gz} to remove the longest matching suffix

B. Use ${file%.gz} to remove only '.gz' suffix

C. Use ${file#*.tar.gz} to remove prefix instead

D. Use ${file%.tar} to remove only '.tar' suffix

Solution

1. Step 1: Understand why ${file%*.gz} removes only '.gz'

   Single % removes shortest suffix matching *.gz pattern, so it matches '.gz' (with * matching empty).

2. Step 2: Use %% to remove longest suffix

   Double %% removes longest matching suffix, so ${file%%*.gz} removes entire '.tar.gz'.

3. Final Answer:

   Use ${file%%*.gz} to remove the longest matching suffix -> Option A

4. Quick Check:

   %% removes longest suffix, % removes shortest [OK]

Hint: Use %% to remove longest suffix pattern [OK]

Common Mistakes:

• Using single % when longest suffix removal needed
• Confusing prefix removal (#) with suffix removal (%)
• Trying to remove partial suffix only

5. You have a list of filenames:

files=("data1.csv" "data2.csv" "notes.txt" "summary.csv")

You want to remove the '.csv' suffix only from files that end with '.csv' using Bash parameter expansion. Which command correctly prints the filenames with '.csv' removed where applicable?

hard

A. for f in "${files[@]}"; do echo ${f%.csv}; done

B. for f in "${files[@]}"; do echo ${f%%csv}; done

C. for f in "${files[@]}"; do echo ${f%csv}; done

D. for f in "${files[@]}"; do echo ${f#%.csv}; done

Solution

1. Step 1: Understand the goal

   Remove '.csv' suffix only if it exists, leave other filenames unchanged.

2. Step 2: Check each option's effect

   A uses single % with '.csv' pattern, removing suffix if present. B uses %%csv missing the dot, incorrect. C misses the dot, incorrect. D uses # which removes prefix, wrong direction.

3. Step 3: Choose best option

   for f in "${files[@]}"; do echo ${f%.csv}; done is correct and simplest for shortest suffix removal of '.csv'.

4. Final Answer:

   for f in "${files[@]}"; do echo ${f%.csv}; done -> Option A

5. Quick Check:

   Use ${var%.csv} to remove '.csv' suffix if present [OK]

Hint: Use ${var%.ext} in loop to trim suffix conditionally [OK]

Common Mistakes:

• Using prefix removal (#) instead of suffix removal (%)
• Omitting the dot in suffix pattern
• Using %% unnecessarily when % suffices