concatenate n lines with sed

Question

Recently, I asked a question how to sort pairs of lines, and one of the answers suggested concatenating lines with sed, like this:

cat file.txt | sed -n 'N;s/\n//;p' | sort -t";" -k43,43n | perl -F';' -ane '$,=";";print @F[0..13],"\n";print @F[14..$#F]'

which worked brilliantly, but now my problem generalized to sorting n-tupels of lines, which I can't figure out how to do with sed.

Everything I found was either for 2 lines or ALL lines, but I need n lines (where n is 5 at the moment, but a general way would be great).

Bonus points for a nice way of rewriting the perl part to accomodate n lines, but the problem is really about the sed part.

I am also not hung on sed specifically, so if you have a nice solution using a different command line tool, please post it.

Update: Example input (n == 3)

a1;b1;c1; 
n1;m1;l1; 
d1;e1;f1;g1
n2;m2;l2;
a2;b2;c2;
d2;e2;f2;g2

Answer 1

sed -e:n -e$\bo -e'N;s/\n/&/4;to' -ebn -e:o -e'y/\n/ /' <in >out

That will concatenate 5 lines - or 1 + 4 lines - replacing each newline with a single space. However:

paste -d\  - - - - - <in >out

...would also work.

Your g sort thing could work like:

paste -d\  - - <input   |
sed 's/.*;\(.*\)/\1;&/' |
sort -t\; -k1,1         |
cut  -d\; -f2-          |
tr \  \\n

...which would be a fairly general way of doing it, though it relies on there being no spaces in the input file. it joins every two lines on a space, the copies the last ; split field to the head of each line, sorts on the first field, then cuts it away and splits the lines back out.

Answer 2

With minor modification, you can use the solution I posted to your other question.

Again using GNU sed and GNU awk and assuming homogeneous structure of the data, use the last element as the sorting key:

# Separate input into records, here 3 lines each
sed '3~3G' infile |

# Use GNU awk's built-in sort, here index-string-descending
awk '
  BEGIN { PROCINFO["sorted_in"] = "@ind_str_desc" }
  { h[$NF] = $0 }
  END { for(k in h) print h[k] }
' RS= FS='[;\n]+'   

Output:

n2;m2;l2;
a2;b2;c2;
d2;e2;f2;g2
a1;b1;c1; 
n1;m1;l1; 
d1;e1;f1;g1