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 AWK script will do the trick:

BEGIN {
    ne=0;
}

/^[[:space:]]*$/ {
    ne++;
}

/[^[:space:]]+/ {
    for(i=0; i < ne; i++)
        print "";
    ne=0;
    print
}

The idea is simple: empty lines do not get echoed immediately. Instead, we wait till we get a non-empty line, and only then we first echo out as much empty lines as seen before it, and only then echo out the new non-empty line.