How to remove multiple newlines at EOF?

From useful one-line scripts for sed.

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

awk '/^$/ {nlstack=nlstack "\n";next;} {printf "%s",nlstack; nlstack=""; print;}' file

Since you already have answers with the more suitable tools sed and awk; you could take advantage of the fact that $(< file) strips off trailing blank lines.

a=$(<file); printf '%s\n' "$a" > file

That cheap hack wouldn't work to remove trailing blank lines which may contain spaces or other non-printing characters, only to remove trailing empty lines. It also won't work if the file contains null bytes.

In shells other than bash and zsh, use $(cat file) instead of $(<file).