Awk Fundamentals

What you’ll practice

• Print fields
• Use separators
• Filter and calculate

The mental model

• awk sees each line as a record and each column as a field.
• $0 is the whole line; $1 is first field; NF is number of fields; NR is line number.

Try it in your terminal

cd ~/linux-practice
echo -e 'Name Age City\nJohn 30 NYC\nJane 25 LA' > data.txt
awk '{print $1, $3}' data.txt
awk '{print NR, $0}' data.txt

echo -e 'Product,Price,Quantity\nApple,1.50,100\nBanana,0.75,200' > inventory.csv
awk -F, 'NR>1 {print $1, $2 * $3}' inventory.csv

awk -F, 'NR>1 {total += $2 * $3} END {print total}' inventory.csv

Put it into practice

1. Create a small expenses.csv and calculate total spending.

Milestone challenge

Build a report from a small CSV: filter the rows you need, transform one value, calculate a total, and save the verified result without changing the source.

Common mistakes

• You run `awk '{print $2}'` on a CSV file and get the wrong column. That's because awk splits on whitespace by default, not commas. Add `-F,` to tell awk your separator is a comma: `awk -F, '{print $2}' inventory.csv`. Without it, 'Apple,1.50,100' is one field, not three.
• You calculate a total with awk and the number is wrong by the first row's amount. Your header row — 'Product,Price,Quantity' — got included in the math. Add `NR>1` to skip it: `awk -F, 'NR>1 {total += $2}' file.csv`. NR is the row number, so NR>1 means 'start from row 2.'

Check your understanding

Explain these in your own words. If you’re unsure, revisit the examples before moving on.

1. What does NR mean?
2. How do you set comma as the field separator?