Coding Macros for Polylines Total Length
That kind of automation is not possible in LT, but there is nothing stopping you using the list command on your selected polylines and copy the results from the command history into excel. And in excel filter the resulting list to just show the lengths of all the polylines, (takes about 30 seconds to do it).
But if you want to try creating a macro you could look at using the lengthen command with the percentage option (use 100%) this updates the perimeter variable to read the length of the selected object, and you can then read that variable using diesel. It's doubtful this will help but it is a way to read length information from objects if you enjoy a challenge.
Accepted solution
Indeed that level of automation is not possible. But should not be possible to miss lengths when you are using the list command and excel. Sometimes copying the command history from Autocad can be a problem as it only holds a limited amount of information. If you turn on "logfiles" and find where Autocad stores those logfiles then that keeps a complete record of everything you do within an Autocad session so it is easy to find the results of the list command and copy that. Look in the Autocad "options" under files tab for where the files are stored or set your own location for logfiles. A unique file is created for every drawing you have open so they are easy to find, plus it is just a text file so once you find the results for the "list" command you can just do a simple copy (or even make a copy of the logfile and change the extension to xls which you can open in excel). In excel select the column of data and first "trim" all the spaces away, then use data to columns and finally filter the column that contains the length keyword. One of your other columns will have all the values which you can easily select. It takes a little while to get used to but once you figure out the sequence and how to just get at the data you need then this does only take less than a minute, whether you have 10 polylines or 100,000.
Accepted solution
@steven-g wrote:
But if you want to try creating a macro you could look at using the lengthen command with the percentage option (use 100%) this updates the perimeter variable to read the length of the selected object, and you can then read that variable using diesel. It's doubtful this will help but it is a way to read length information from objects if you enjoy a challenge.
Thankyou Steven, I had no idea that value was stored in a variable. I wish I had known earlier.
Challenge accepted! 
Is this what you had in mind? (Tested on LT2013)
*^C^C$m=$(if,$(or,$(eq,$(getenv,pgm_c),0),$(eq,$(getenv,pgm_c),)),_select;"""$m=$(if,$(getvar,cmdactive),\)"""$(if,$(and,$(getvar,menuecho),5),,^p)menuecho;3;$(if,$(and,$(getvar,menuecho),4),^p)_setenv;pgm_c;5)$(if,$(eq,$(getenv,pgm_c),5),_setenv;pgm_pickfirst;$(getvar,pickfirst);;pgm_selectsimilarmode;$(getvar,selectsimilarmode);;pgm_expert;$(getvar,expert);;pgm_clayer;$(getvar,clayer);;pgm_c;10)$(if,$(eq,$(getenv,pgm_c),10),"_setenv;pgm_c;0;_expert;5;_-block;@selset@;0,0;previous;;oops;;_-bedit;@selset@;_zoom;_extents;_-layer;_thaw;`@selset`@;_unlock;`@selset`@;_make;@selset@;;_setenv;pgm_c;15")$(if,$(eq,$(getenv,pgm_c),15),_setenv;pgm_c;0;_selectsimilarmode;0;_pickfirst;1;setenv;pgm_totlen;0;;pgm_c;20)$(if,$(eq,$(getenv,pgm_c),20),"_setenv;pgm_c;0;_line;_none;0,0;_none;10,0;;_selectsimilar;last;;_chprop;_layer;@selset@;;_erase;_last;;_setenv;pgm_c;21")$(if,$(eq,$(getenv,pgm_c),21),"_setenv;pgm_c;0;_pline;_none;0,0;_none;10,0;;_selectsimilar;last;;_chprop;_layer;@selset@;;_erase;_last;;_setenv;pgm_c;22")$(if,$(eq,$(getenv,pgm_c),22),"_setenv;pgm_c;0;_3dpoly;_none;0,0;_none;10,0;;_selectsimilar;last;;_chprop;_layer;@selset@;;_erase;_last;;_setenv;pgm_c;23")$(if,$(eq,$(getenv,pgm_c),23),"_setenv;pgm_c;0;^r_spline;_none;0,0;_none;10,0;;_selectsimilar;last;;_chprop;_layer;@selset@;;_erase;_last;;_setenv;pgm_c;24")$(if,$(eq,$(getenv,pgm_c),24),"_setenv;pgm_c;0;_circle;_none;5,5;5;_selectsimilar;last;;_chprop;_layer;@selset@;;_erase;_last;;_setenv;pgm_c;25")$(if,$(eq,$(getenv,pgm_c),25),"_setenv;pgm_c;0;_arc;_none;0,0;_none;5,5;_none;10,0;_selectsimilar;last;;_chprop;_layer;@selset@;;_erase;_last;;_setenv;pgm_c;26")$(if,$(eq,$(getenv,pgm_c),26),"_setenv;pgm_c;0;_ellipse;_none;0,5;_none;10,5;_none;5,10;_selectsimilar;last;;_chprop;_layer;@selset@;;_erase;_last;;_setenv;pgm_c;30")$(if,$(eq,$(getenv,pgm_c),30),_setenv;pgm_c;0;_selectsimilarmode;$(getenv,pgm_selectsimilarmode);_pickfirst;$(getenv,pgm_pickfirst);_-layer;_off;*;_on;`@selset`@;;expert;$(getenv,pgm_expert);_setenv;pgm_c;loop)$(if,$(eq,$(getenv,pgm_c),loop),_select;_single;_last;"""$m=$(if,$(getvar,cmdactive),^c_setenv;pgm_c;0;_bsave;_bclose;_layerp;;;_-purge;_blocks;`@selset`@;_no;;_layers;`@selset`@;_no;_menuecho;0;_getenv;pgm_msg;$,_setenv;pgm_c;100)""")$(if,$(eq,$(getenv,pgm_c),100),_setenv;pgm_c;0;_lengthen;last;_percent;100;;_erase;_last;;"""$m=_setenv;pgm_totlen;$(+,$(getenv,pgm_totlen),$(getvar,perimeter));;pgm_c;110""")$(if,$(eq,$(getenv,pgm_c),110),_setenv;pgm_msg;""""""""""Total length: $(rtos,$(getenv,pgm_totlen))"""""""""";;pgm_c;loop)
@Anonymous
This macro should do what you are looking for:
Simply select the linear objects (lines, polylines, 3dpolylines, splines, arcs, circles or ellipses) you wish to add up the lengths of and the macro will loop through them and give you the total at the end. The macro filters out any non-linear objects such as text, dimensions, hatches etc. in order to avoid it crashing when it uses the lengthen command to set the perimeter variable. However, I recommend you set up filters to help you select only the objects you want, such as lines on particular layers or polylines with certain widths and colours, for example. The total is displayed in the format determined by your current unit settings.
When pasting the code into the CUI editor, I suggest you open the long string editor in the macro field to make sure it's all copied and check that there are no spaces or returns at the end of the code.
@Johneng Thankyou for recommending my spreadsheet. I'm glad you found it useful.
Works fine for me, admittedly I don't have the benefit of your drawing which might have some odd objects, but a quick test with just a few polylines in 2022.1 and the macro still performs as well as ever.
Do you get any error messages?
Maybe turn 'on' logfiles' and post a copy of the results here so we can see where the macro might be tripping up. A copy of a dwg file showing which items you select would also help us try and pinpoint the problem.