$ cat foo
    #!/usr/bin/env bash

    set -e
    echo -n 'echo "$0":                               '
    echo "$0"

    echo -n 'echo "$(dirname $(realpath $0))":        '
    echo "$(dirname $(realpath $0))"

    echo -n 'echo "$(dirname "$(realpath "$0")")":    '
    echo "$(dirname "$(realpath "$0")")"

    echo -n 'echo "$(dirname "$(realpath -- "$0")")": '
    echo "$(dirname "$(realpath -- "$0")")"

$ foo
    echo "$0":                               /home/sjl/bin/foo
    echo "$(dirname $(realpath $0))":        /home/sjl/bin
    echo "$(dirname "$(realpath "$0")")":    /home/sjl/bin
    echo "$(dirname "$(realpath -- "$0")")": /home/sjl/bin

$ ./foo
    echo "$0":                               ./foo
    echo "$(dirname $(realpath $0))":        /home/sjl/bin
    echo "$(dirname "$(realpath "$0")")":    /home/sjl/bin
    echo "$(dirname "$(realpath -- "$0")")": /home/sjl/bin

$ bash foo
    echo "$0":                               foo
    echo "$(dirname $(realpath $0))":        /home/sjl/bin
    echo "$(dirname "$(realpath "$0")")":    /home/sjl/bin
    echo "$(dirname "$(realpath -- "$0")")": /home/sjl/bin

$ mv foo 'foo bar'

$ 'foo bar'
    echo "$0":                               /home/sjl/bin/foo bar
    echo "$(dirname $(realpath $0))":        /home/sjl/bin
    /home/sjl/bin
    echo "$(dirname "$(realpath "$0")")":    /home/sjl/bin
    echo "$(dirname "$(realpath -- "$0")")": /home/sjl/bin

$ ./'foo bar'
    echo "$0":                               ./foo bar
    echo "$(dirname $(realpath $0))":        /home/sjl/bin
    /home/sjl/bin
    echo "$(dirname "$(realpath "$0")")":    /home/sjl/bin
    echo "$(dirname "$(realpath -- "$0")")": /home/sjl/bin

$ bash 'foo bar'
    echo "$0":                               foo bar
    echo "$(dirname $(realpath $0))":        /home/sjl/bin
    /home/sjl/bin
    echo "$(dirname "$(realpath "$0")")":    /home/sjl/bin
    echo "$(dirname "$(realpath -- "$0")")": /home/sjl/bin

$ mv 'foo bar' -- --help

$ --help
    echo "$0":                               /home/sjl/bin/--help
    echo "$(dirname $(realpath $0))":        /home/sjl/bin
    echo "$(dirname "$(realpath "$0")")":    /home/sjl/bin
    echo "$(dirname "$(realpath -- "$0")")": /home/sjl/bin

$ ./--help
    echo "$0":                               ./--help
    echo "$(dirname $(realpath $0))":        /home/sjl/bin
    echo "$(dirname "$(realpath "$0")")":    /home/sjl/bin
    echo "$(dirname "$(realpath -- "$0")")": /home/sjl/bin

$ bash -- --help
    echo "$0":                               --help
    echo "$(dirname $(realpath $0))":        dirname: invalid option -- 'e'
    Try 'dirname --help' for more information.

    echo "$(dirname "$(realpath "$0")")":    Usage: realpath [OPTION]... FILE...
    Print the resolved absolute file name;
    all but the last component must exist

      -e, --canonicalize-existing  all components of the path must exist
      -m, --canonicalize-missing   no path components need exist or be a directory
      -L, --logical                resolve '..' components before symlinks
      -P, --physical               resolve symlinks as encountered (default)
      -q, --quiet                  suppress most error messages
          --relative-to=DIR        print the resolved path relative to DIR
          --relative-base=DIR      print absolute paths unless paths below DIR
      -s, --strip, --no-symlinks   don't expand symlinks
      -z, --zero                   end each output line with NUL, not newline

          --help     display this help and exit
          --version  output version information and exit

    GNU coreutils online help: <http://www.gnu.org/software/coreutils/>
    Full documentation at: <http://www.gnu.org/software/coreutils
    echo "$(dirname "$(realpath -- "$0")")": /home/sjl/bin