awk

Basic Filtering

By default, it treats spaces/tabs as delimiters. This can be changed using -F'<del>'.

# extract the first field
awk '{print $1}' <file>
# extract multiple fields
awk '{print $1,$4}' <file>

Line Filtering

$NF (number of fields) represents the last field, while $NR (number of records) represents the total number of records.

# start from the 3rd line and print the last field.
awk 'NR > 3 {print $NF}' <file>

Printf

Whatever is within {} is the awk script that will be executed for each input line:

1. printf is a built-in awk function, which formats and prints data.

2. "%s " defines the string format: the output should be a string (%s) followed by a space.

3. $0 represents the entire current line of input in awk.

# for each input line, print the entire line and add a space after it
awk '{printf "%s ", $0}'

We can add a newline character at the end using an END block:

1. END {...} actions within an END block are executed after all input lines have been processed.

awk '{printf "%s ", $0} END {print ""}'