Here is a lisp that collects the lengths of lines or polylines on selected layers:

;;; LENLYR.LSP a program to find the length of all
;;; entities on any selected layer
;;;
(defun err (s)
  (if (= s "Function cancelled")
    (princ "\nLENLYR - cancelled: ")
    (progn (princ "\nLENLYR - Error: ") (princ s)
    (terpri))
  ); if
  (resetting)
  (princ "SYSTEM VARIABLES have been reset\n")
  (princ)
); err
(defun setv (systvar newval)
   (setq x (read (strcat systvar "1")))  
   (set x (getvar systvar))
   (setvar systvar newval)
); setv
(defun setting ()
   (setq oerr *error*)
   (setq *error* err)
   (setv "CMDECHO" 0)
   (setv "BLIPMODE" 0)
); end of setting
(defun rsetv (systvar)
   (setq x (read (strcat systvar "1")))
   (setvar systvar (eval x))
); restv
(defun resetting ()
   (rsetv "CMDECHO")
   (rsetv "BLIPMODE")
   (setq *error* oerr)
); end of resetting

(defun dxf (code ename)
  (cdr (assoc code (entget ename)))
); dxf

(defun lenlyr ( / LayerList EntityList EntityLengths)
  (setq LayerList (get-lyrs)
        EntityList (get-ents LayerList)
        EntityLengths (do-len EntityList)
  ) ; setq
  (prin1 (read (rtos EntityLengths 2 2)))
); lenlyr

(defun get-lyrs ( / isent lyr-list ss i lname)
  (setq isent nil lyr-list nil)
  (prompt
       "\nSelect object(s) on required layer(s): ")
  (setq ss nil)
  (while (not ss)
    (setq ss (ssget))
    (if (not ss)
        (prompt "\nNo entities were selected.")
    ); if
  ); while
  (setq i (- 1))
  (repeat (sslength ss)
    (setq lname (dxf 8 (ssname ss (setq i (1+ i)))))
    (if (not (member lname lyr-list)) 
      (setq lyr-list (append lyr-list (list lname)))
    ); if
  ); repeat
  lyr-list
); get-lyrs

(defun get-ents (LayerList / lstr lst lyr str
      filtlist i ss ename elist)
  (setq lstr (strcat (car LayerList) ","))
  (setq lst (cdr LayerList))
  (foreach lyr lst
    (setq str (strcat lyr ",")
          lstr (strcat lstr str)
    ); setq
  ); foreach
  (setq lstr (substr lstr 1 (1- (strlen lstr))))
  (setq filtlist (list
       (cons 8 lstr)
        '(-4 . "<or")
          '(0 . "LINE")
          '(0 . "ARC")
          '(0 . "CIRCLE")
          '(0 . "POLYLINE")
          '(0 . "LWPOLYLINE")
        '(-4 . "or>")
    ); list
  ); setq
  (setq i (- 1) elist nil ss nil)
  (setq ss (ssget "X" filtlist))
  (if ss
    (progn
      (repeat (sslength ss)
        (setq ename (ssname ss (setq i (1+ i))))
        (setq elist (append elist (list ename)))
      ); repeat
      (princ (strcat "\nTotal length of all "
            "entities on layer(s) " lstr ": ")
      ); print
     ); progn
     (progn
       (alert (strcat "No eligible entities on "
                "layer(s) \n" lstr "\naborting."))
       (exit)
     ); progn
   ); if
  elist
); get-ents

(defun do-len (EntityList / TotalLength ent len)
  (setq TotalLength 0 len 0)
  (foreach ent EntityList
    (setq len (ent-len ent))
    (if len
      (setq TotalLength (+ len TotalLength))
    ); if
  ); foreach
); do-len

(defun ent-len (en / elength)
  (setq elength
    (cond
      ((= (dxf 0 en ) "LINE") (do-line en))
      ((= (dxf 0 en ) "ARC") (do-arc en))
      ((= (dxf 0 en ) "CIRCLE") (do-circle en))
      ((= (dxf 0 en ) "POLYLINE") (do-pline en))
      ((= (dxf 0 en ) "LWPOLYLINE") (do-lwpline en))
    ); cond
  ); setq
  elength
); ent-len

(defun do-line (en / p10 p11 len)
  (setq p10 (dxf 10 en)
        p11 (dxf 11 en)
        len (distance p10 p11)
  ); setq
  len
); do-line

(defun do-arc (en / rad sang eang theta len)
  (setq rad (dxf 40 en)
        sang (dxf 50 en)
        eang (dxf 51 en)
        theta (- eang sang)
  ); setq
  (if (minusp theta)
    (setq theta (+ theta pi pi))
  ); if
  (setq len (* rad theta))
); do-arc

(defun do-circle (en / rad len)
  (setq rad (dxf 40 en)
        len (* rad pi 2)
  ); setq
  len
); do-circle

(defun do-pline (en / is-closed vlist vvlist len)
  (setq is-closed (dxf 70 en))
  (if (/= is-closed 100)
    (progn
      (setq en (entnext en))
      (setq vlist nil
            vvlist nil
      ); setq
      (while (/= "SEQEND" (dxf 0 en))
        (setq vlist (dxf 10 en)
              vlist (reverse vlist)
              vlist (cdr vlist)
              vlist (list (reverse vlist))
        ); setq
        (setq vlist
          (append vlist (list (dxf 42 en))))
        (setq vvlist (append vvlist (list vlist)))
        (setq en (entnext en))
      ); while
    ); progn
  ); if
  (setq len (do-polylen vvlist is-closed))
); do-pline

(defun do-lwpline (en / num-vert is-closed elist
     vlist vvlist len)
  (setq num-vert (dxf 90 en)
        is-closed (dxf 70 en)
        elist (entget en)
        elist (member (assoc 10 elist) elist)
        vlist nil
        vvlist nil
  ); setq
  (repeat num-vert
    (setq vlist (list (cdr (assoc 10 elist))))
    (setq vlist
       (append vlist (list (cdr (assoc 42 elist)))))
    (setq vvlist (append vvlist (list vlist)))
    (setq elist (cdr elist)
          elist (member (assoc 10 elist) elist)
    ); setq
  ); repeat
  (setq len (do-polylen vvlist is-closed))
); do-lwpline

(defun do-polylen (vvlist is-closed / closed seglen
     plen first p10 p11 bulge)
  (setq closed (logand is-closed 1)
        seglen 0
        plen 0
  ); setq
  (if (= closed 1)
    (progn
      (setq first (car vvlist)
            vvlist (append vvlist (list first))
      ); setq
    ); progn
  ); if
  (repeat (1- (length vvlist))
    (setq p10 (caar vvlist)
          p11 (caadr vvlist)
          bulge (cadar vvlist)
    ); setq
    (setq seglen (do-seg p10 p11 bulge))
    (setq plen (+ plen seglen))
    (setq vvlist (cdr vvlist))
  ); repeat
  plen
); do-polylen

(defun do-seg (p1 p2 bulg / seglen ang4 ang dis rad)
  (if (= bulg 0.0)
    (progn
       (setq seglen (distance p1 p2))
    ); progn
    (progn
      (setq ang4 (atan bulg)
            ang (* 4.0 ang4)
            dis (distance p1 p2)
            rad (/ (/ dis 2.0) (sin (/ ang 2.0)))
            seglen (* rad ang)
       ); setq
    ); progn
  ); if
  seglen
); do-seg

(defun c:lnl ()
   (setting)
   (lenlyr)
   (resetting)
   (princ)
); c:lnl

(prompt "\nEnter LNL to start")

Olá,

I have some AutoLISP applications (written in portuguese and not translated yet) in my site  that return the total of perimeters, areas and volumes (3dsolids).
Some have the possibility to put the result in text, but you can just try the somaper.lsp (http://www.cadtom.com/Arquivo/AutoLISP/Somaper.zip). It shows on commands line the total length of select AutoCAD entities.
Write somaper in the commands line.

Sometimes I choose some lines with a list command to obtain the lenght of them, but this is so bored when take a lot of lines , curves, etc. , I will apreciatte if somebody can help me to obtain the sum total of them more quickly