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

this can be solved easily with sed -z option

sed -rz 's/^\n+//; s/\n+$/\n/g' file
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