Shell Programming and Scripting

Either you add an empty line to the end of infile by using (echo "" >> infile) then execute or modify the code to below

Code:

awk 'NR>1 && ($1 != p) {print a[c-1]"\n"a[c] ; c=0} {p=$1 ; a[++c]=$0 }
END{print  a[c-1]"\n"a[c] }' infile

Except for the first line read, it checks to see when the first field changes (a->b, b->c, etc). When this happens, it prints out the desired lines (using the pr_lines function) which have been collected in an array. At end of file, pr_lines is run again to print any lines since the last printing

$ cat a.awk

Code:

function pr_lines() { for (i=j-N; i<j; i++) print a[i]; j=0 }
$1!=old1 && NR!=1 { pr_lines() }
{ a[j++]=$0; old1=$1 }
END { pr_lines() }

$ awk -v N=1 -f a.awk data
a 4
b 4
c 4

$ awk -v N=2 -f a.awk data
a 3
a 4
b 3
b 4
c 3
c 4

awk -v N=3 -f a.awk data
a 2
a 3
a 4
b 2
b 3
b 4
c 2
c 3
c 4

Thank you danmero ,ahmad.diab, thegeek and alister for all your efforts.

It's been a good experience with AWK. I'll dig deep into this stuff.

The problem has been solved.

Thank you once again.

Cheers,
14341

Ops , we should work after the END

Code:

awk 'END{print a,b}$1!=x && a{print a,b}{a=b;b=$0;x=$1}' OFS="\n" file

Should work now