Shell Programming and Scripting

$ cat file_lines_to_insert => contents are
abc
def
lkj

x=$(sed '/PIN (new)/!d;=;d;q' final-file)
# check if x has value and not 1
# ...
sed "$((x-1))r inser-file" final-file

awk 'NR==FNR{a=a==""?$0:a RS $0;next}
      /PIN/{print a}1' file_lines_to_insert final_file

sed -e '/PIN (new)/r file_lines_to_insert' -e 'x' final_file

'/PIN (new)/r file_lines_to_insert'  => When this pattern matches lines from file_lines_to_insert in inserted.

'x' => This command helps to switch the content of pattern buffer with hold buffer. So when 1st line is read 'x' puts the 1st line to hold buffer 
       and pattern buffer takes a new-line char, after this switch what ever there is in pattern buffer is printed, that's why a new line is printed
       first in the output.
       Now 2nd line is read, 'x' puts 2nd line into hold buffer and line 1 which is already in hold buffer comes to pattern buffer and line 1 now gets printed. 
       This action repeats for all the remaining lines.