How to use unix tool AWK

This artical will help you understand how to work with the AWK utility in UNIX. It also gives
the meaning of some of the AWK Built-in Variables

These few AWK one liners give very basic and random examples which will help to understand basic about this UNIX tool.

Meaning of some of the Awk Built-in Variables used below:

NF               : Number of fields in current line/record

NR               : Ordial number of current line/record

FS                : Field Separator (Also -F can be used)

OFS             : Output Field Separator (default=blank)

FILENAME : Name of current input file

All of following Awk one liner examples is based on the input file 'test1.txt’

$ cat test1.txt                                                               

Continent:Val

AS:12000

AF:9800                                                               

AS:12300

NA:3400

OC:12000

AF:500

AS:1000

Know more bout UNIX FILE PERMISSIONS   Click here

Scenario	Print 'line number' NR and 'Number of fields' NF for each line
Command	awk -F ":" '{print NR,NF}' test1.txt
Output	1 2
	2 2
	3 2
	4 2
	5 2
	6 2
	7 2
	8 2
Scenario	Print first field, colon delimited
Command	awk -F ":" '{print $1}' test1.txt
	Continent
	AS
	AF
	AS
	NA
	OC
	AF
	AS
Scenario	Print first field, colon delimited, but excluding the 'first line' (NR!=1)
Command	awk -F ":" 'NR!=1 {print $1}' test1.txt
Output	AS
	AF
	AS

	NA
	OC
	AF
	AS
Scenario	Print first field, colon delimited, but only for line number 1 (NR==1)
Command	awk -F ":" 'NR==1 {print $1}' test1.txt
Output	Continent
Scenario	Print first and second field, colon delimited, but excluding the 'first line' (NR!=1)
Command	awk -F ":" 'NR!=1 {print $1,$2}' test1.txt
Output	AS 12000
	AF 9800
	AS 12300
	NA 3400
	OC 12000
	AF 500
	AS 1000
Scenario	Setting output field separator as pipe
Command	awk -F ":" 'BEGIN{OFS="|"} NR!=1 {print $1,$2}' test1.txt
Output	AS|12000
	AF|9800
	AS|12300
	NA|3400
	OC|12000
	AF|500
	AS|1000
Scenario	Anything on BEGIN executes first
Command	awk 'BEGIN{FS=":"; OFS="|"; print "Con|SomeVal"} NR!=1 {print $1,$2}' test1.txt
Output	Con|SomeVal
	AS|12000
	AF|9800
	AS|12300
	NA|3400
	OC|12000
	AF|500
	AS|1000
Scenario	Printing FILENAME, will be printed for all the lines
Command	awk -F ":" '{print FILENAME}' test1.txt
Output	test1.txt
	test1.txt
	test1.txt
	test1.txt
	test1.txt
	test1.txt
	test1.txt
	test1.txt

Scenario	Printing FILENAME, but printing only last instance using END clause
Command	awk -F ":" ' END {print FILENAME}' test1.txt
Output	test1.txt
Scenario	Printing the last field of the file, same as printing $2 as there are only 2 fields
Command	awk -F ":" '{print $NF}' test1.txt
Output	Val
	12000
	9800
	12300
	3400
	12000
	500
	1000
Scenario	Matching, printing lines begin with "AS"
Command	awk -F ":" '/^AS/' test1.txt
Output	AS:12000
	AS:12300
	AS:1000
Scenario	Matching, printing lines not begining with "AS"
Command	awk -F ":" '!/^AS/' test1.txt
Output	Continent:Val
	AF:9800
	NA:3400
	OC:12000
	AF:500
Scenario	Direct matching, first field as "AS"
Command	awk -F ":" '$1=="AS"' test1.txt
Output	AS:12000
	AS:12300
	AS:1000
Scenario	Direct matching, first field as "AS", Print 2nd Column
Command	awk -F ":" '$1=="AS" {print $2}' test1.txt
Output	12000
	12300
	1000
Scenario	$0 prints the full line, same as {print}
Command 1	awk -F ":" '$1=="AS" {print $0}' test1.txt
Output	AS:12000
	AS:12300
	AS:1000

Command 2	awk -F ":" '$1=="AS" {print}' test1.txt
Output	AS:12000
	AS:12300
	AS:1000
Scenario	'Or' and 'AND' together
Command	awk -F ":" '($1=="AS" || $1=="OC") && $NF > 11000 {print}' test1.txt
Output	AS:12000
	AS:12300
	OC:12000
Scenario	Partial Matching
Command	awk -F ":" '$1 ~ /A/ {print}' test1.txt
Output	AS:12000
	AF:9800
	AS:12300
	NA:3400
	AF:500
	AS:1000
Scenario	Reading from STDOUT
Command	cat test1.txt | awk -F ":" '!/Continent/ {print $1}' | sort | uniq
Output	AF
	AS
	NA
	OC
Scenario	Add value 1000 to the 2nd field, where first field is "AF" and then print the output file
Command	awk -F ":" '$1=="AF" {$2+=1000} {print}' test1.txt
Output	Continent:Val
	AS:12000
	AF 10800
	AS:12300
	NA:3400
	OC:12000
	AF 1500
	AS:1000
Scenario	Sum of 2nd fields, exclude first line
Command	awk -F ":" 'NR!=1 {sum+=$NF} END {print sum}' test1.txt
Output	51000
Scenario	Set 2nd value as 0 where first field is "AS"
Command	awk -F ":" 'BEGIN {OFS=":"} $1=="AS" {$2=0} {print}' test1.txt
Output	Continent:Val
	AS:0
	AF:9800
	AS:0
	NA:3400