awk field extraction in scripts in Bash Scripting - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print the second field of each line using awk.

Bash Scripting

awk '{ print $[1] }' file.txt

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

A2

B0

C1

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using $1 instead of $2 prints the first field.

Using $0 prints the whole line, not a single field.

The $2 in awk prints the second field of each line.

2fill in blank

medium

Complete the code to print the first and third fields separated by a dash.

Bash Scripting

awk '{ print $[1] "-" $3 }' data.txt

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

A1

B3

C0

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Using $2 instead of $1 prints the wrong field.

Forgetting to add quotes around the dash causes syntax errors.

Using $1 and $3 prints the first and third fields. The dash is added as a string between them.

3fill in blank

hard

Fix the error in the code to print the last field of each line.

Bash Scripting

awk '{ print $[1] }' file.txt

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

ANR

BNF

C0

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using NR prints the line number, not a field.

Using $0 prints the whole line, not a single field.

NF is a special awk variable that holds the number of fields in the current line, so $NF prints the last field.

4fill in blank

hard

Fill both blanks to print fields 2 and 4 separated by a comma.

Bash Scripting

awk '{ print $[1] "," $[2] }' input.txt

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

A2

B3

C4

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up field numbers causes wrong output.

Forgetting quotes around the comma causes syntax errors.

To print the second and fourth fields, use $2 and $4 separated by a comma string.

5fill in blank

hard

Fill all three blanks to create a dictionary of word lengths for words longer than 3 characters.

Bash Scripting

awk '{ if(length($[1]) > [2]) print $[3], length($[3]) }' words.txt

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

A1

B3

C2

D4

Attempts:

3 left

💡 Hint

Common Mistakes

Using $2 instead of $1 prints wrong fields.

Using 4 instead of 3 changes the filter condition.

We check the length of the first field ($1) to be greater than 3, then print the word ($1) and its length.

Practice

1. What does awk '{print $2}' file.txt do in a bash script?

easy

A. Prints the second word (field) from each line of file.txt

B. Prints the entire line from file.txt

C. Prints the first word (field) from each line of file.txt

D. Prints the number of lines in file.txt

Solution

1. Step 1: Understand awk field numbering

   Awk splits each line into fields separated by spaces by default. $1 is the first field, $2 is the second, and so on.

2. Step 2: Analyze the command

   The command prints $2, which is the second field of each line in file.txt.

3. Final Answer:

   Prints the second word (field) from each line of file.txt -> Option A

4. Quick Check:

   Awk $2 prints second field [OK]

Hint: Remember $1 is first field, $2 second, etc. [OK]

Common Mistakes:

• Confusing $2 with line number
• Thinking it prints entire line
• Mixing up field numbers starting at 0

2. Which of the following is the correct syntax to print the third field using awk with a comma as the field separator?

easy

A. awk -F ',' '{print $3}' file.csv

B. awk '{print $3 -F ','}' file.csv

C. awk '{print $3, -F ","}' file.csv

D. awk -F ';' '{print $3}' file.csv

Solution

1. Step 1: Identify field separator option

   The -F option sets the field separator. For comma-separated files, use -F ','.

2. Step 2: Check print syntax

   The correct print syntax is '{print $3}' to print the third field.

3. Final Answer:

   awk -F ',' '{print $3}' file.csv -> Option A

4. Quick Check:

   Use -F ',' before script block [OK]

Hint: Use -F 'separator' before the awk script block [OK]

Common Mistakes:

• Placing -F inside the print statement
• Using wrong separator like semicolon for CSV
• Misplacing quotes around separator

3. Given a file data.txt with the following content:

apple 10 red
banana 5 yellow
cherry 20 red

What is the output of awk '{print $1, $3}' data.txt?

medium

A. apple 10
banana 5
cherry 20

B. apple red
banana yellow
cherry red

C. 10 red
5 yellow
20 red

D. apple banana cherry

Solution

1. Step 1: Identify fields in each line

   Each line has three fields: $1=fruit, $2=number, $3=color.

2. Step 2: Print first and third fields

   The command prints $1 and $3 separated by space, so output lines are fruit and color pairs.

3. Final Answer:

   apple red banana yellow cherry red -> Option B

4. Quick Check:

   Print $1 and $3 fields [OK]

Hint: Match $1, $2, $3 to columns in data [OK]

Common Mistakes:

• Printing wrong fields like $2 instead of $3
• Confusing field order
• Expecting numbers instead of colors

4. What is wrong with this awk command to print the first field from a colon-separated file?
awk '{print $1}' -F ':' file.txt

medium

A. The colon separator is invalid in awk

B. The $1 should be $0 to print the whole line

C. The -F option should come before the script block

D. The file name should come before the script block

Solution

1. Step 1: Check placement of -F option

   The -F option must come before the script block in awk commands.

2. Step 2: Analyze the command structure

   Correct syntax is: awk -F ':' '{print $1}' file.txt

3. Final Answer:

   The -F option should come before the script block -> Option C

4. Quick Check:

   -F before script block [OK]

Hint: Put -F before the '{print ...}' block [OK]

Common Mistakes:

• Placing -F after the script block
• Using wrong field variable
• Misordering file name and script

5. You have a file records.txt with lines like:

John|Doe|30|Engineer
Jane|Smith|25|Designer
Bob|Brown|40|Manager

Write an awk command to print only the names (first and last) of people older than 28.

hard

A. awk -F '|' '$3 < 28 {print $1, $2}' records.txt

B. awk -F ',' '$3 > 28 {print $1, $2}' records.txt

C. awk '{if ($3 > 28) print $1, $2}' records.txt

D. awk -F '|' '$3 > 28 {print $1, $2}' records.txt

Solution

1. Step 1: Set correct field separator

   The file uses '|' as separator, so use -F '|' to split fields correctly.

2. Step 2: Filter by age and print names

   Use condition $3 > 28 to select lines where age is greater than 28, then print first and second fields (first and last names).

3. Final Answer:

   awk -F '|' '$3 > 28 {print $1, $2}' records.txt -> Option D

4. Quick Check:

   Filter $3 > 28 and print $1, $2 [OK]

Hint: Use -F '|' and condition $3 > 28 to filter [OK]

Common Mistakes:

• Using wrong field separator
• Using wrong comparison operator
• Not filtering before printing