Shell Programming and Scripting

awk '
END{                    ###So this is awks END section which will be executed when ALL the Input_file(s) are done with reading by awk. 
print NR+1-length(ARGV) ###Now doing print of value of NR+1-length(ARGV) where NR value is the value of all the lines of Input_files(total of all lines of all files) then adding 1 to it and
                        ###Subtracting the value of length of array ARGV, array named ARGV is the default array for awk which will have the total number of Input_file(s) passed to it.
}                       ###So let's say you passed 3 files so its value will be 3 and value of headings will also be 3 so I am subtracting those lines which have headings in them as per your request.
' *.txt                 ###Mentioning all the .txt Input_file(s) here.

awk 'FNR>1 {n++} END {print n+0}' *.txt