Transform variable length line into multiple lines with specific selected fields, retaining first and last delimited column on each line

Question

I have output from a firewall configuration that contains lines with data in a specific format. I need to transform this data for a spreadsheet to split groups of 4 columns from each line into a new, while retaining the first and last delimited fields of the line from which it came, then removing the first line.

I've attempted to use awk, ed, rs, tr, and can't seem to figure out how to properly do this. Each line is a different length, but the fields will always be a group of 4 starting at the second delimited field. So fields 2,3,4,5; 6,7,8,9; 10,11,12,13; 14,15,16,17, etc... length of lines could be up to 128 fields

The data i'm attempting to transform looks as follows

startoflinesampletext_25;10.2.8.13;25;10.2.8.13%2;25;10.2.8.14;25;10.2.8.14%2;25;10.2.8.15;25;10.2.8.15%2;25;10.2.8.56;25;10.2.8.56%2;25;10.2.8.57;25;10.2.8.57%2;25;endoflinesampletext

The expected result I'm hoping for would look like this :

startoflinesampletext_25;10.2.8.13;25;10.2.8.13%2;25;endoflinesampletext
startoflinesampletext_25;10.2.8.14;25;10.2.8.14%2;25;endoflinesampletext
startoflinesampletext_25;10.2.8.15;25;10.2.8.15%2;25;endoflinesampletext
startoflinesampletext_25;10.2.8.56;25;10.2.8.56%2;25;endoflinesampletext
startoflinesampletext_25;10.2.8.57;25;10.2.8.57%2;25;endoflinesampletext

Answer 1

awk to the rescue!

$ awk -F';' 'BEGIN{OFS=FS} {for(i=2;i<NF;i+=4) print $1,$i,$(i+1),$(i+2),$(i+3),$NF}' file

startoflinesampletext_25;10.2.8.13;25;10.2.8.13%2;25;endoflinesampletext
startoflinesampletext_25;10.2.8.14;25;10.2.8.14%2;25;endoflinesampletext
startoflinesampletext_25;10.2.8.15;25;10.2.8.15%2;25;endoflinesampletext
startoflinesampletext_25;10.2.8.56;25;10.2.8.56%2;25;endoflinesampletext
startoflinesampletext_25;10.2.8.57;25;10.2.8.57%2;25;endoflinesampletext

note that there is no validation that the fields are multiple of four.

Answer 2

This might work for you (GNU sed):

sed -E 's/^(([^;]*)(;[^;]*){4})(.*(;.*))$/\1\5\n\2\4/;P;D' file

Replace the fourth ; by the last field, followed by a newline, followed by the first field, print/delete the first line and repeat. The iteration whittles down the string until pattern matching no longer works and the last record is printed by default.