Inserting Lines between data sets using SED?

Shell Programming and Scripting
1

Hello all and thanks in advance!
What I'm looking to do is insert a blank line, anytime the first 9 characters of a given line don't match the first 9 characters of the previous line.

i.e.
Convert the data set

1 45 64 89
1 89 69 235
2 89 234 67
2 56 90 23
to because 1 and 2 don't match.
1 45 64 89
1 89 69 235

2 89 234 67
2 56 90 23

However the expression in the first few charachters will change throughout the input file, so anytime there is a difference i'll need to insert a new line.

I can't quite figure out how to carry the expression I need to match from line to line, nor how to insert the line in the correct position!

Thanks
Josh

2

Hi,
I suppose your requirements is as follow:

INPUT:

123456789avadf
123456789iowqeuroi
123456780fdkljfdsa
123456789kljasdgl;kj
123456789nm,zxcvn

OUTPUT:

123456789avadf
123456789iowqeuroi

123456780fdkljfdsa

123456789kljasdgl;kj
123456789nm,zxcvn

CODE:

cat c | awk '{
if (pre=="")
{
	print $0
}
else
{
	if (substr($0,1,9)!=pre)
	{
		print ""
		print $0
	}
	else
	{
		print $0
	}
}
pre=substr($0,1,9)
}'