echo 'first line to add' >> file
echo 'second line to add' >> file
echo 'third line to add' >> file
or:
echo 'first line to add
second line to add
third line to add' >> file
一击必中。
So, tying these two ideas together, if you wanted to get the first 10 lines of the input.txt file to output.txt and append a line with five "=" characters, you could use something like:
( head -10 input.txt ; echo '=====' ) > output.txt