awk basics (field processing) in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this awk command?

Given a file data.txt with the following content:

apple 10
banana 20
cherry 30

What is the output of this command?

awk '{print $2}' data.txt

Linux CLI

awk '{print $2}' data.txt

A

apple
banana
cherry

B

10
20
30

C

1
2
3

D

apple 10
banana 20
cherry 30

💡 Hint

Remember, $2 means the second field in each line.

The awk command prints the second field ($2) from each line. The second fields are 10, 20, and 30.

💻 Command Output

intermediate

What does this awk command print?

Given the same data.txt file:

apple 10
banana 20
cherry 30

What is the output of this command?

awk '{print $1 "-" $2}' data.txt

Linux CLI

awk '{print $1 "-" $2}' data.txt

A

apple-10
banana-20
cherry-30

B

apple 10
banana 20
cherry 30

C

10-apple
20-banana
30-cherry

D

apple
banana
cherry

💡 Hint

The command joins the first and second fields with a dash.

The print statement concatenates $1, a dash, and $2, producing lines like apple-10.

📝 Syntax

advanced

Which awk command correctly prints the third field?

Choose the correct awk command to print the third field from a file.

A awk '{print $3;}' file.txt

B awk '{print $[3]}' file.txt

C awk '{print $3}' file.txt

D awk '{print $-3}' file.txt

💡 Hint

Field variables in awk use $ followed by the field number without brackets or signs.

Only $3 is valid syntax to print the third field. $[3] and $-3 are invalid. The semicolon in A is allowed but option C is simpler and correct.

🔧 Debug

advanced

Why does this awk command produce an error?

Consider this command:

awk '{print $1 + $2}' data.txt

Given data.txt contains:

apple 10
banana 20
cherry 30

Why does it produce an error or unexpected output?

Linux CLI

awk '{print $1 + $2}' data.txt

A Because $2 is not a valid field

B Because awk requires a comma between fields in print

C Because the file is missing a header line

D Because $1 is a string and cannot be added to a number directly

💡 Hint

Think about how awk treats strings and numbers in arithmetic.

Awk tries to convert $1 and $2 to numbers for addition. Since $1 is 'apple' (a string), it converts to 0, so output is 0+10=10 for first line, which may be unexpected.

🚀 Application

expert

How many lines will this awk command print?

Given data.txt contains:

apple 10
banana 20
cherry 30
42 100

What is the number of lines printed by this command?

awk '$1 ~ /^[a-z]+$/ {print $0}' data.txt

Linux CLI

awk '$1 ~ /^[a-z]+$/ {print $0}' data.txt

A 3

B 4

C 1

D 0

💡 Hint

The regex matches lines where the first field is only lowercase letters.

The first three lines have first fields 'apple', 'banana', 'cherry' which match the regex. The last line '42' does not match, so 3 lines print.