Adding a blank line after every 5th line

Shell Programming and Scripting
1

Hello...
I have a file which contain certain number of records.
I want to generate another file from this file which will contain 1st line as a blank line & after every 5 lines one blank line will be inserted. How to achieve this through shell scripting?

Thanks...

2 
awk '{ print; } NR % 5 == 0 { print ""; }' inputfile...
3

Lets say I have file FILE1 which contains 100 records.

FILE1
------------

aaaaaaaaaaaa
bbbbbbbbbbbb
cccccccccccc
dddddddddddd
eeeeeeeeeeee
fffffffffffffffffff
gggggggggggg
hhhhhhhhhhhh
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii
jjjjjjjjjjjjjjjjjjjjjjj
kkkkkkkkkkkkk
lllllllllllllllllllllllllllll
mmmmmmmmm
nnnnnnnnnnnn
oooooooooooooo
ppppppppppppppp

I want to add a header record before the first record & after every 5th record so that file will look like this.

record set-1
aaaaaaaaaaaa
bbbbbbbbbbbb
cccccccccccc
dddddddddddd
eeeeeeeeeeee
record set-2
fffffffffffffffffff
gggggggggggg
hhhhhhhhhhhh
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii
jjjjjjjjjjjjjjjjjjjjjjj
record set-3
kkkkkkkkkkkkk
lllllllllllllllllllllllllllll
mmmmmmmmm
nnnnnnnnnnnn
oooooooooooooo
record set-4
ppppppppppppppp

How to achieve this?

4 
awk '(NR-1)%5||$0="record set-"++i RS $0' infile
5 
awk ' BEGIN {print "record set -1"; rec=1}
        {print $0 
        if (NF%5 == 0 ) {rec++; print "record set -" rec} } ' infile > outfile

try that

6

Or:

awk 'NR % 5 == 1 { print "record set-" ++rec; } { print; }' inputfile

> TIMTOWTDI