in reply to Combine files with same extension in new file

Depending on your use case, a simple one-liner may work:

perl -lne 'print unless /header contents/' file1 file2 file3 > new_file

if the header is varying but can be characterized by a known pattern, or

perl -lne 'print if $. > 3 } continue { close ARGV if eof' file1 file2 file3 > new_file

if the header has a fixed, known size (3 lines in this example).