commandline remeshing and simplifying tools
Netfabb came up in a number of suggestions that I found. Take a look at 3D Printing Under Arch Linux, which offers a number of solutions for Linux, including:


OpenSCAD
FreeCAD
Blender
NetFabb
Slic3r


Netfabb

Taking the section on Netfabb:


  netfabb Private will provide you with a fully-loaded tool-box to do all this and much more:
  
  
  fix complicated file errors
  make late design changes
  combine parts into one
  hollow out solid parts into a shell
  smooth the mesh to improve surfaces
  reduce file size
  


Installing it:


  netfabb is not at official repository so you must install it from AUR
  using yaourt

$ yaourt netfabb-basic
$ netfabb-basic



However, it is unclear as to whether there is a cmd line interface. It could be worth reading Problem in Netfabb Command Line execution and in particular the documentation on Automating Netfabb - although this seems to suggest that command line functionality is only available to users with Ultimate subscription and not Basic:


  


From Reducing Size of STL file to upload to shapeways, this post (#10) states:


  You can also decimate the model in Netfabb easily - Right click > Level of Detail > Choose something like 50%... or more or less depending on the level of detail needed.


Although, this isn't available in Basic subscription, or so says post #12.



Meshmixer

I also came across this, non-command line option.

From How to Reduce the File Size of .STL and .OBJ 3D Models


  For example, you can give the free 3D modeling program Meshmixer a try. Choose the ‘Select’ tool from the menu on the right, then double-click on your model (this will select your entire mesh). Then click on the ‘Edit…’ option and select ‘Reduce’.
  
  You can now reduce the polygon count using several options. The best working choice is to use the percentage tool. It will immediately tell you by how much percent your file size (and polygon count) has been reduced.


Available for Windows and OSX.

From Reducing Size of STL file to upload to shapeways, this post (#8) states:


  The meshlab tutorial is exactly what you want to do - the options described help preserve the overall geometry of the model while reducing the poly count. Start with a target of 150,000 polys and work up until the desired detail is retained, bearing in mind the printability I mentioned above.


Also, by way of Quora, How do I reduce the size of an STL file? Does it affect the CAD coordinates for 3D printing?, I also found this Meshmixer tutorial: Easy Guide on How to Repair Your .STL Files. Under the section Problem 4: File Size is too Large for 3D Printing are the following steps:


  The last problem that you may stumble upon, particularly as your
  objects get larger and their complexity increases, is that the
  resulting .stl file size is too large for your 3D printer or 3D
  printing service of choice. Third party printing services like
  i.materialise or Shapeways  have upload limits so you may have to
  change the size of your file (100&nbsp;MB limit at imaterialise and 64&nbsp;MB for
  Shapeways). It’s important to reduce the mesh without sacrificing the
  quality, which I should say at the outset is best done at the initial
  export from your CAD software to minimise any distortion. My number one quick
  tip is to make sure in the export settings that your saving in
  ‘Binary’ format, not ‘ASCII’ –  it’s a significantly more compact file
  format for .stl’s without losing quality). However if it’s not an
  option, Meshmixer can be really useful to quickly reduce file size and
  visualise how this will affect the quality of your surfaces.
  
  For this example I’m going to return to the leaf from Problem 1, which
  as a .stl file is 30.757&nbsp;MB – pretty large for such a small design and
  definitely over the limit for someone’s email if I wanted to send it.
  So let’s look at how we can get this under 10&nbsp;MB.
  
  
  Select the entire model by pressing Ctrl + A on your keyboard to select all.
  Go to Edit>Reduce to bring up the options to reduce the mesh. Essentially the file size of a .stl is directly related to the number
  of polygons (triangles) that make up all of the surfaces. We will use
  the Reduce tool to reduce the quantity of polygons, therefore reducing
  file size.
  The menu will give you a range of options to reduce the size of your file. The simplest is to use the default Percentage option,
  allowing you to determine the final file size you want rather than
  needing to know exactly how many triangles will be used to make up the
  file. In this case I have calculated that in order to get my original
  .stl file below 10&nbsp;MB, I need a reduction of 70&nbsp;% or more. As you
  adjust the values, you will get a preview of what your model will look
  like, allowing you to control how much reduction you employ before the
  model becomes too distorted and ‘pixelated.’
  
  
  
  
  
  Once you’re happy and have accepted the changes, you can click on the Export button or go to File>Export to save this new reduced .stl
  file. As you can see in the comparison below, there is almost no
  perceptible difference in the quality of the 30.757&nbsp;MB file compared
  with the final reduced version at 9.362&nbsp;MB. I have simply increased the
  size of the triangles, minimising the quantity needed to create the
  same volume. Your regular 3D printer, or even a highly accurate SLS
  printer will never even know the difference in a change like this.
  It’s only if you really go crazy with the file reduction that you
  might start to notice them in your final print (and in fact many of
  the low-poly models which are popular on Pinshape can be produced
  using this technique – start with a detailed .stl of the object you
  want, and then just keep reducing the number of triangles!).
  
  
  


Blender

From Reducing Size of STL file to upload to shapeways, this post (#8) states:


  Another option is to import the model into Blender, then use the Remesh or Decimate modifiers. Blender can be tough to get into initially but there are plenty of introduction tutorials on YouTube to help.


Blender does offer a Command Line Interface (CLI), see Command Line Arguments:

Usage: blender [args …] [file] [args …]


However, there doesn't appear to be an option for Remesh or Decimate. Although take a look at Is it possible to decimate or remesh via the CLI?:


  You can specify a Python script to run, see the Python Options section of the documentation you linked. In this script, you can import the model, add the modifiers, apply them and export the result. 


Related - Is it possible to automatically simplify geometry in blender without losing object shape?, which has this comment:


  Is there a way to execute this modifier from command line and export the result? 


which then leads to Can modifiers be computed and applied from the command line?


  You'd have to use bpy.ops.object.modifier_apply, e.g.

import bpy

for obj in bpy.context.scene.objects:
    bpy.context.scene.objects.active = obj
    count = 1
    length = len(obj.modifiers)
    while obj.modifiers:
        name = obj.modifiers[0].name
        print("%s: Applying %s (%d/%d)" % (obj, name, count, length))
        bpy.ops.object.modifier_apply(modifier=name)
        count += 1
print("All done.")

  
  For info on how to to run the above, see here.


Meshlab

Seeing as you are already using Meshlab, it might be worth reading Executing meshlab from commandline reduce faces of a mesh iteratively (awesomebytes/reduce_faces.py)

#!/usr/bin/env python

import sys
import os
import subprocess

# Script taken from doing the needed operation
# (Filters &gt; Remeshing, Simplification and Reconstruction &gt;
# Quadric Edge Collapse Decimation, with parameters:
# 0.9 percentage reduction (10%), 0.3 Quality threshold (70%)
# Target number of faces is ignored with those parameters
# conserving face normals, planar simplification and
# post-simplimfication cleaning)
# And going to Filter &gt; Show current filter script
filter_script_mlx = """&lt;!DOCTYPE FilterScript&gt;
&lt;FilterScript&gt;
 &lt;filter name="Quadric Edge Collapse Decimation"&gt;
  &lt;Param type="RichInt" value="1448" name="TargetFaceNum"/&gt;
  &lt;Param type="RichFloat" value="0.9" name="TargetPerc"/&gt;
  &lt;Param type="RichFloat" value="0.3" name="QualityThr"/&gt;
  &lt;Param type="RichBool" value="false" name="PreserveBoundary"/&gt;
  &lt;Param type="RichFloat" value="1" name="BoundaryWeight"/&gt;
  &lt;Param type="RichBool" value="true" name="PreserveNormal"/&gt;
  &lt;Param type="RichBool" value="false" name="PreserveTopology"/&gt;
  &lt;Param type="RichBool" value="false" name="OptimalPlacement"/&gt;
  &lt;Param type="RichBool" value="true" name="PlanarQuadric"/&gt;
  &lt;Param type="RichBool" value="false" name="QualityWeight"/&gt;
  &lt;Param type="RichBool" value="true" name="AutoClean"/&gt;
  &lt;Param type="RichBool" value="false" name="Selected"/&gt;
 &lt;/filter&gt;
&lt;/FilterScript&gt;
"""


def create_tmp_filter_file(filename='filter_file_tmp.mlx'):
    with open('/tmp/' + filename, 'w') as f:
        f.write(filter_script_mlx)
    return '/tmp/' + filename


def reduce_faces(in_file, out_file,
                 filter_script_path=create_tmp_filter_file()):
    # Add input mesh
    command = "meshlabserver -i " + in_file
    # Add the filter script
    command += " -s " + filter_script_path
    # Add the output filename and output flags
    command += " -o " + out_file + " -om vn fn"
    # Execute command
    print "Going to execute: " + command
    output = subprocess.check_output(command, shell=True)
    last_line = output.splitlines()[-1]
    print
    print "Done:"
    print in_file + " &gt; " + out_file + ": " + last_line


if __name__ == '__main__':
    if len(sys.argv) &lt; 3:
        print "Usage:"
        print sys.argv[0] + " /path/to/input_mesh num_iterations"
        print "For example, reduce 10 times:"
        print sys.argv[0] + " /home/myuser/mymesh.dae 10"
        exit(0)

    in_mesh = sys.argv[1]
    filename = in_mesh.split('/')[-1]
    num_iterations = int(sys.argv[2])

    folder_name = filename.replace('.', '_')
    tmp_folder_name = '/tmp/' + folder_name + '_meshes/'

    print "Input mesh: " + in_mesh + " (filename: " + filename + ")"
    print "Num iterations: " + str(num_iterations)
    print "Output folder: " + tmp_folder_name
    try:
        os.mkdir(tmp_folder_name)
    except OSError as e:
        print &gt;&gt; sys.stderr, "Exception creating folder for meshes: " + str(e)
        exit(0)
    for it in range(1, num_iterations):
        if it == 1:
            out_mesh = tmp_folder_name + folder_name + "_it" + str(it) + ".dae"
            reduce_faces(in_mesh, out_mesh)
        else:
            out_mesh = tmp_folder_name + folder_name + "_it" + str(it) + ".dae"
            reduce_faces(last_out_mesh, out_mesh)
        last_out_mesh = out_mesh

    print
print "Done reducing, find the files at: " + tmp_folder_name


Also


  here are some updates for python 3.6.2: https://gist.github.com/tylerlindell/7435ca2261e7c404ccc1241f18e483aa