Why patterns solve common automation needs in Bash Scripting - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print all files in the current directory.

Bash Scripting

for file in [1]; do echo "$file"; done

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

A*

Becho

Cpwd

Dls

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'ls' directly in the loop variable, which causes errors.

Using 'pwd' which prints the current directory path, not files.

The asterisk (*) matches all files in the current directory, so the loop prints each file name.

2fill in blank

medium

Complete the code to check if a file named 'data.txt' exists.

Bash Scripting

if [[ [1] "data.txt" ]]; then echo "File exists"; fi

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

A-f

B-e

C-s

D-d

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-d' which checks for directories only.

Using '-s' which checks if file size is greater than zero.

The '-e' option checks if the file exists, regardless of type.

3fill in blank

hard

Fix the error in the code to count lines in 'log.txt'.

Bash Scripting

count=$(cat log.txt | [1] -l)

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

Als

Bgrep

Cwc

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'ls -l' which lists files, not lines.

Using 'grep -l' which lists filenames matching a pattern.

'wc -l' counts the number of lines in the input. The original code misses the command 'wc'.

4fill in blank

hard

Fill both blanks to create a loop that prints numbers 1 to 5.

Bash Scripting

for num in [1]; do echo [2]; done

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

A{1..5}

Bnum

C$num

D1 2 3 4 5

Attempts:

3 left

💡 Hint

Common Mistakes

Printing 'num' without '$' prints the word 'num' literally.

Using 'num' instead of a sequence in the loop.

'{1..5}' generates numbers 1 to 5. '$num' prints the current number in the loop.

5fill in blank

hard

Fill all three blanks to create a dictionary-like structure with file sizes.

Bash Scripting

declare -A sizes
for file in [1]; do sizes[[2]]=$(stat -c [3] "$file"); done
for f in "${!sizes[@]}"; do echo "$f: ${sizes[$f]} bytes"; done

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

A*

Bfile

C%s

D%n

Attempts:

3 left

💡 Hint

Common Mistakes

Using '%n' which returns the file name, not size.

Using incorrect keys in the associative array.

'*' matches all files. 'file' is the key for the associative array. '%s' gets file size in bytes with stat.

Practice

1. Why are patterns useful in bash scripting automation?

easy

A. They provide reusable solutions to common tasks.

B. They make scripts run faster by using special commands.

C. They allow scripts to run without any errors always.

D. They automatically fix bugs in your code.

Solution

1. Step 1: Understand what patterns mean in scripting

   Patterns are common ways to solve repeated problems efficiently.

2. Step 2: Identify the benefit of using patterns

   They save time and reduce errors by reusing tested solutions.

3. Final Answer:

   They provide reusable solutions to common tasks. -> Option A

4. Quick Check:

   Patterns = reusable solutions [OK]

Hint: Patterns = repeatable solutions that save time [OK]

Common Mistakes:

• Thinking patterns speed up script execution
• Believing patterns fix all bugs automatically
• Confusing patterns with error-free guarantees

2. Which of the following is the correct syntax to start a bash script with a pattern for error handling?

easy

A. #!/bin/bash
error -set

B. #!/bin/bash
set -e

C. #!/bin/bash
set error

D. #!/bin/bash
set +e

Solution

1. Step 1: Recall the standard bash shebang line

   It starts with #!/bin/bash to specify the interpreter.

2. Step 2: Identify the correct command to stop on errors

   set -e tells bash to exit on any error, a common pattern.

3. Final Answer:

   #!/bin/bash set -e -> Option B

4. Quick Check:

   set -e = exit on error pattern [OK]

Hint: Use 'set -e' to stop script on errors [OK]

Common Mistakes:

• Using 'set +e' which disables error exit
• Writing 'error -set' which is invalid syntax
• Confusing 'set error' as a command

3. What will be the output of this script snippet using a common pattern to loop over files?

for file in *.txt; do
  echo "$file"
done

medium

A. Prints the string '*.txt' literally

B. Throws an error if no .txt files exist

C. Lists all files ending with .txt in the current directory

D. Lists all files in the directory regardless of extension

Solution

1. Step 1: Understand the for loop pattern over files

   The loop iterates over all files matching the pattern '*.txt'.

2. Step 2: Determine what echo prints each iteration

   It prints the current filename matching the pattern.

3. Final Answer:

   Lists all files ending with .txt in the current directory -> Option C

4. Quick Check:

   for file in *.txt = list .txt files [OK]

Hint: for file in *.txt loops over matching files [OK]

Common Mistakes:

• Expecting literal '*.txt' output
• Assuming error if no matches (depends on shell settings)
• Thinking it lists all files, not filtered

4. This script is intended to stop on errors but does not. What is the error?

#!/bin/bash
set +e
cp file1.txt file2.txt

medium

A. Using 'set +e' disables exit on error, so script continues

B. Missing quotes around filenames causes error

C. The shebang line is incorrect

D. The cp command syntax is wrong

Solution

1. Step 1: Check the meaning of 'set +e'

   It disables the exit-on-error behavior, allowing script to continue.

2. Step 2: Understand why script does not stop on error

   Because 'set +e' is used, errors won't stop the script.

3. Final Answer:

   Using 'set +e' disables exit on error, so script continues -> Option A

4. Quick Check:

   set +e disables error exit [OK]

Hint: Use 'set -e' to stop on errors, not 'set +e' [OK]

Common Mistakes:

• Confusing +e and -e options
• Thinking quotes are mandatory for cp here
• Assuming shebang line causes error

5. You want to create a bash script pattern that processes only non-empty text files in a directory. Which snippet correctly applies this pattern?

hard

A. for f in *.txt; do echo "$f"; done

B. for f in *.txt; do if [[ -z "$f" ]]; then echo "$f"; fi; done

C. for f in *.txt; do if [[ -f "$f" ]]; then echo "$f"; fi; done

D. for f in *.txt; do if [[ -s "$f" ]]; then echo "$f"; fi; done

Solution

1. Step 1: Identify the test for non-empty files

   Using [[ -s "$f" ]] checks if file size is greater than zero (non-empty).

2. Step 2: Confirm the loop processes only .txt files and echoes them if non-empty

   The loop iterates over *.txt files and echoes only those passing the size test.

3. Final Answer:

   for f in *.txt; do if [[ -s "$f" ]]; then echo "$f"; fi; done -> Option D

4. Quick Check:

   Use [[ -s file ]] to check non-empty files [OK]

Hint: Use [[ -s file ]] to filter non-empty files [OK]

Common Mistakes:

• Using [[ -z ]] which checks for empty files
• Using only [[ -f ]] which checks if file exists but not size
• Not filtering files at all