How awk Works

The awk command is a command line tool for processing and analyzing text that works by lines and columns. It is essentially a small program that reads data, selects parts of lines, operates on them and prints the result. It shines brightest when processing tables, logs and CSV files.

awk '{ print $1 }' file.txt

What Is awk

The name awk comes from the surnames of its three authors: Aho, Weinberger and Kernighan. It splits each line of input text into fields (columns) separated by spaces. Fields are accessible as variables $1 through $NF, and the whole line as $0.

Printing Columns

The most common use of awk is printing a specific column from text. Column 1 is $1, the last column is $NF (number of fields).

cat names.txt
# output: Ana Smith 34

awk '{ print $2 }' names.txt
# output: Smith

awk '{ print $NF }' names.txt
# output: 34

Matching Patterns

A condition or pattern can be placed before the block of commands. Commands are executed only on lines that match the pattern.

awk '/error/ { print }' log.txt # prints lines containing the word error
awk '$3 > 30 { print $1, $3 }' names.txt # lines where column 3 is greater than 30

Changing Field Separator

The default field separator is a space. For processing CSV files we change it with the -F flag.

awk -F ';' '{ print $2 }' data.csv # fields separated by semicolon

Calculations and Sums

awk can also do arithmetic and sum up all lines. The variable NF is the number of fields in a line, NR is the current line number.

awk '{ sum += $3 } END { print sum }' names.txt # sums column 3
awk 'END { print NR }' file.txt # prints the number of lines

These basic commands cover most everyday text processing tasks — printing columns, filtering by pattern and simple calculations. Anyone who wants to dig deeper will discover that awk can do much more.