Sed snippets

3-line cycle

    1 N
    $ { p; q }
    N

    # ... your conditions ...

    P; D

    :end_cycle
        n; h; H; g; N; D

    # ... your loops ...

Delete multiple empty lines and hanging empty lines in '{}' blocks (C/C++)

    N
    $ { p; q }
    /^\s*\n\s*}/ D
    /^\s*\{\n\s*$/ { P; n; h; H; g; D }
    /^\s*\n\s*$/ D
    P; D