abspath

#! .desc:
# Convert a relative pathname into an absolute pathname
#! .params:
# <"$1"> - path
#! .uses.var:
# <PWD> $ - environment variable;
#           absolute pathname of the current working directory
#! .gives:
# <"$_path"> - string;
#              [absolute <$1>]
#! .rc:
# (0) success
#! .ec:
# (255) bad input
#.
abspath() {
    [ "$1" ] || exit 255

    # Use $PWD (absolute pathname of the current working directory) to convert
    # a relative path into an absolute one if it's not already.
    #
    # For more information, refer to:
    # > "POSIX.1-2024, Volume: Base Definitions, Section: Definitions,
    #   Subsection: Absolute Pathname".
    # > "POSIX.1-2024, Volume: Base Definitions, Section: Definitions,
    #   Subsection: Relative Pathname".
    # > "POSIX.1-2024, Volume: Base Definitions, Section: Environment
    #   Variables, Subsection: Environment Variable Definition".
    # > "POSIX.1-2024, Volume: Base Definitions, Section: Environment
    #   Variables, Subsection: Other Environment Variables".
    case "$1" in
        '/'*) _path="$1" ;;
        *) _path="${PWD%/}/$1" ;;
    esac

    return 0
}