source: vendor/bash/3.1/examples/functions/external

# Contributed by Noah Friedman.

# To avoid using a function in bash, you can use the `builtin' or
# `command' builtins, but neither guarantees that you use an external
# program instead of a bash builtin if there's a builtin by that name.  So
# this function can be used like `command' except that it guarantees the
# program is external by first disabling any builtin by that name.  After
# the command is done executing, the state of the builtin is restored. 
function external ()
{
 local state=""
 local exit_status
  
    if builtin_p "$1"; then
       state="builtin"
       enable -n "$1"
    fi

    command "$@"
    exit_status=$?

    if [ "$state" = "builtin" ]; then
       enable "$1"
    fi

    return ${exit_status}
}

# What is does is tell you if a particular keyword is currently enabled as
# a shell builtin.  It does NOT tell you if invoking that keyword will
# necessarily run the builtin.  For that, do something like
#
#       test "$(builtin type -type [keyword])" = "builtin"
#
# Note also, that disabling a builtin with "enable -n" will make builtin_p
# return false, since the builtin is no longer available.
function builtin_p ()
{
 local word

    set $(builtin type -all -type "$1")

    for word in "$@" ; do
       if [ "${word}" = "builtin" ]; then
          return 0
       fi
    done

    return 1
}