emacs -Q
M-x run-octave ;; now emacs keeps busy until you press C-g to cancel.
C-g ;; now there is a buffer named *Inferior Octave* indeed.
M-x run-octave ;; split window, popup *Inferior Octave*
C-x o ;; switch back to *scratch* buffer
M-x octave-mode ;;
1+2 ;; goto octave mode and enter some text.
C-c TAB C-l ;; octave-send-line. Now emacs keeps busy until you send C-g.

by the way I have apt-get installed octave in my system.

In GNU Emacs 24.3.1 (x86_64-pc-linux-gnu, GTK+ Version 3.10.7)
of 2014-03-08 on lamiak, modified by Debian
Windowing system distributor `The X.Org Foundation', version 11.0.11501000
System Description: Ubuntu 14.04 LTS

Configured using:
`configure '--build' 'x86_64-linux-gnu' '--build' 'x86_64-linux-gnu'
'--prefix=/usr' '--sharedstatedir=/var/lib' '--libexecdir=/usr/lib'
'--localstatedir=/var/lib' '--infodir=/usr/share/info'
'--mandir=/usr/share/man' '--with-pop=yes'
'--enable-locallisppath=/etc/emacs24:/etc/emacs:/usr/local/share/emacs/24.3/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/24.3/site-lisp:/usr/share/emacs/site-lisp'

'--with-crt-dir=/usr/lib/x86_64-linux-gnu' '--with-x=yes'
'--with-x-toolkit=gtk3' '--with-toolkit-scroll-bars'
'build_alias=x86_64-linux-gnu' 'CFLAGS=-g -O2 -fstack-protector
--param=ssp-buffer-size=4 -Wformat -Werror=format-security -Wall'
'LDFLAGS=-Wl,-Bsymbolic-functions -Wl,-z,relro'
'CPPFLAGS=-D_FORTIFY_SOURCE=2''

Important settings:
value of $LC_CTYPE: zh_CN.UTF-8
value of $LC_MONETARY: en_US.UTF-8
value of $LC_NUMERIC: en_US.UTF-8
value of $LC_TIME: en_US.UTF-8
value of $LANG: en_US.UTF-8
value of $XMODIFIERS: @im=fcitx
locale-coding-system: utf-8-unix
default enable-multibyte-characters: t

Major mode: Octave

Minor modes in effect:
tooltip-mode: t
mouse-wheel-mode: t
tool-bar-mode: t
menu-bar-mode: t
file-name-shadow-mode: t
global-font-lock-mode: t
font-lock-mode: t
blink-cursor-mode: t
auto-composition-mode: t
auto-encryption-mode: t
auto-compression-mode: t
line-number-mode: t
transient-mark-mode: t

Recent input:
M-x r u n - o c t a v e <return> M-x r u n - o c t
a v e <return> C-x o 1 + 2 C-c TAB M-x o c t a v e
- m o d e <return> C-c TAB C-l M-x r e p o r t - e
<tab> <return>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Quit [2 times]

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr emacsbug message format-spec rfc822 mml
mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev
gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util
mail-prsvr mail-utils octave-inf comint ansi-color ring octave-mod smie
easymenu time-date china-util tooltip ediff-hook vc-hooks
lisp-float-type mwheel x-win x-dnd tool-bar dnd fontset image regexp-opt
fringe tabulated-list newcomment lisp-mode register page menu-bar
rfn-eshadow timer select scroll-bar mouse jit-lock font-lock syntax
facemenu font-core frame cham georgian utf-8-lang misc-lang vietnamese
tibetan thai tai-viet lao korean japanese hebrew greek romanian slovak
czech european ethiopic indian cyrillic chinese case-table epa-hook
jka-cmpr-hook help simple abbrev minibuffer loaddefs button faces
cus-face macroexp files text-properties overlay sha1 md5 base64 format
env code-pages mule custom widget hashtable-print-readable backquote
make-network-process dbusbind dynamic-setting system-font-setting
font-render-setting move-toolbar gtk x-toolkit x multi-tty emacs)