What is $NF in awk Command

Source: wikipedia

In awk, $NF is a special variable that represents the value of the last field in the current record being processed. The NF built-in variable in awk holds the total number of fields in the current record, and when you use $NF, it directly accesses the value of the field that corresponds to that number.

Example Usage

Consider the following input file data.txt:

Alice 30 Engineer
Bob 25 Designer
Charlie 35 Manager

You can use an awk command to print the last field (job title) of each line:

awk '{ print $NF }' data.txt

Output:

Engineer
Designer
Manager

Explanation:

• In each line of the file data.txt, awk splits the line into fields based on whitespace (the default behavior).
• For the first line, NF would be 3 (for "Alice", "30", "Engineer"), so $NF refers to Engineer.
• For the second line, it refers to Designer, and for the third line, it refers to Manager.

More Examples

Print the Last Field with Line Number:

awk '{ print NR ": " $NF }' data.txt

Output:

1: Engineer
2: Designer
3: Manager

Check if the Last Field Matches a Specific Value:

awk '$NF == "Manager" { print $1 }' data.txt

Output:

Charlie

This command prints names where the last field is “Manager”.

Sum the Second Field but Only Print the Last Field:

awk '{ sum += $2 } END { print "Total age is:", sum; print "Last field in last line is:", $NF }' data.txt

Output:

Total age is: 90
Last field in last line is: Manager

Note that in the last statement, $NF refers to the last field of the last line processed by awk.

The $NF variable is very useful when dealing with data where the number of fields can vary from line to line, allowing you to grab the last field dynamically.

In this video, using the awk command and its internal variables such as $1 and $NF, as well as combining the awk and rev commands, we find the first and last word in a string.

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