#! /bin/sh
# Please back up your files before runing this script.
# Use sed to delete row 1 to row 6 for all .txt files 
#  in the current direcotry tree (including sub-folders).
find . -type f -name '*.txt' -print | while read file
do
  sed '1,6d' $file > $file.tmp && mv $file.tmp $file
done