Count occurrences per key

Frequency count of the first field (e.g. IP addresses)

awk '{count[$1]++} END {for (k in count) print count[k], k}' access.log | sort -rn

More awk commands

Print last field

awk '{print $NF}' file.txt

NF holds the number of fields; $NF is the last field
Multi-condition filter

awk '$2 > 500 && $5 == "POST"' access.log

Print lines where field 2 > 500 AND field 5 is POST
Reformat output

awk '{printf "%-20s %5d\n", $1, $2}' data.txt

Aligned printf formatting with fixed column widths
Run awk script from file

awk -f transform.awk input.txt

Load awk program from an external script file
In-place-style transform with awk

awk '{gsub(/foo/, "bar"); print}' input.txt > tmp && mv tmp input.txt

Global substitution and write back to same file