Recipe : Basic awk primer


$ echo -e "line1\nline2" | awk 'BEGIN{ print "Start" } { print } END{ print "End" } ' 
Start 
line1 
line2 
End 



$ echo -e "line1 f2 f3\nline2 f4 f5\nline3 f6 f7" | \

awk '{
 print "Line no:"NR",No of fields:"NF, "$0="$0, "$1="$1,"$2="$2,"$3="$3 
}' 
Line no:1,No of fields:3 $0=line1 f2 f3 $1=line1 $2=f2 $3=f3 
Line no:2,No of fields:3 $0=line2 f4 f5 $1=line2 $2=f4 $3=f5 
Line no:3,No of fields:3 $0=line3 f6 f7 $1=line3 $2=f6 $3=f7


Summing numbers from each line
==============================
$ seq 5 | awk 'BEGIN{ sum=0; print "Summation:" } 
{ print $1"+"; sum+=$1 } END { print "=="; print sum }' 
Summation: 
1+ 
2+ 
3+ 
4+ 
5+ 
==
15


Passing a variable value from outside to awk
============================================
$ VAR=10000
$ echo | awk -v VARIABLE=$VAR'{ print VARIABLE }
1


getline var
===========
$ seq 5 | awk 'BEGIN { getline; print "Read ahead first line", $0 } { print $0 }' 
Read ahead first line 1 
2 
3 
4 
5 


Filtering lines processed by awk with filter patterns
=====================================================
$ awk 'NR < 5' # Line number less than 5
$ awk 'NR==1,NR==4' #Line numbers from 1-5
$ awk '/linux/' # Lines contianing the pattern linux (We can specify regex)
$ awk '!/linux/' # Lines not containing pattern linux



Setting delimiter for fields
============================
$ awk -F: '{ print $NF }' /etc/passwd

$ awk  'BEGIN { FS=":" } { print $NF }' /etc/passwd