Removing trailing / starting newlines with sed, awk, tr, and friends

Question

I would like to remove all of the empty lines from a file, but only when they are at the end/start of a file (that is, if there are no non-empty lines before them, at the start;

Answer 1

From Useful one-line scripts for sed:

# Delete all leading blank lines at top of file (only).
sed '/./,$!d' file

# Delete all trailing blank lines at end of file (only).
sed -e :a -e '/^\n*$/{$d;N;};/\n$/ba' file

Therefore, to remove both leading and trailing blank lines from a file, you can combine the above commands into:

sed -e :a -e '/./,$!d;/^\n*$/{$d;N;};/\n$/ba' file