diff --git a/doc/devel/matlab_example1.py b/doc/devel/matlab_example1.py
index aaf6c4cb3a..9f15389669 100644
--- a/doc/devel/matlab_example1.py
+++ b/doc/devel/matlab_example1.py
@@ -1,13 +1,17 @@
 from nipype.interfaces.matlab import MatlabCommand
-from nipype.interfaces.base import TraitedSpec, \
-    BaseInterface, BaseInterfaceInputSpec, File
+from nipype.interfaces.base import (
+    TraitedSpec,
+    BaseInterface,
+    BaseInterfaceInputSpec,
+    File,
+)
 import os
 from string import Template
 
 
 class ConmapTxt2MatInputSpec(BaseInterfaceInputSpec):
     in_file = File(exists=True, mandatory=True)
-    out_file = File('cmatrix.mat', usedefault=True)
+    out_file = File("cmatrix.mat", usedefault=True)
 
 
 class ConmapTxt2MatOutputSpec(TraitedSpec):
@@ -19,14 +23,15 @@ class ConmapTxt2Mat(BaseInterface):
     output_spec = ConmapTxt2MatOutputSpec
 
     def _run_interface(self, runtime):
-        d = dict(in_file=self.inputs.in_file,
-                 out_file=self.inputs.out_file)
+        d = dict(in_file=self.inputs.in_file, out_file=self.inputs.out_file)
         # This is your MATLAB code template
-        script = Template("""in_file = '$in_file';
+        script = Template(
+            """in_file = '$in_file';
                              out_file = '$out_file';
                              ConmapTxt2Mat(in_file, out_file);
                              exit;
-                          """).substitute(d)
+                          """
+        ).substitute(d)
 
         # mfile = True  will create an .m file with your script and executed.
         # Alternatively
@@ -43,5 +48,5 @@ def _run_interface(self, runtime):
 
     def _list_outputs(self):
         outputs = self._outputs().get()
-        outputs['out_file'] = os.path.abspath(self.inputs.out_file)
+        outputs["out_file"] = os.path.abspath(self.inputs.out_file)
         return outputs
diff --git a/doc/devel/matlab_example2.py b/doc/devel/matlab_example2.py
index 8d683ea45f..7d75e307b1 100644
--- a/doc/devel/matlab_example2.py
+++ b/doc/devel/matlab_example2.py
@@ -4,8 +4,7 @@
 
 
 class HelloWorldInputSpec(MatlabInputSpec):
-    name = traits.Str(mandatory=True,
-                      desc='Name of person to say hello to')
+    name = traits.Str(mandatory=True, desc="Name of person to say hello to")
 
 
 class HelloWorldOutputSpec(TraitedSpec):
@@ -29,6 +28,7 @@ class HelloWorld(MatlabCommand):
     >>> out = hello.run()
     >>> print out.outputs.matlab_output
     """
+
     input_spec = HelloWorldInputSpec
     output_spec = HelloWorldOutputSpec
 
@@ -37,7 +37,9 @@ def _my_script(self):
         script = """
         disp('Hello %s Python')
         two = 1 + 1
-        """ % (self.inputs.name)
+        """ % (
+            self.inputs.name
+        )
         return script
 
     def run(self, **inputs):
diff --git a/nipype/interfaces/mrtrix3/__init__.py b/nipype/interfaces/mrtrix3/__init__.py
index 9ea9850b1b..126192030f 100644
--- a/nipype/interfaces/mrtrix3/__init__.py
+++ b/nipype/interfaces/mrtrix3/__init__.py
@@ -15,6 +15,7 @@
     DWIExtract,
     SHConv,
     SH2Amp,
+    MRCat,
 )
 from .preprocess import (
     ResponseSD,
diff --git a/nipype/interfaces/mrtrix3/tests/test_auto_MRCat.py b/nipype/interfaces/mrtrix3/tests/test_auto_MRCat.py
new file mode 100644
index 0000000000..5659da4507
--- /dev/null
+++ b/nipype/interfaces/mrtrix3/tests/test_auto_MRCat.py
@@ -0,0 +1,73 @@
+# AUTO-GENERATED by tools/checkspecs.py - DO NOT EDIT
+from ..utils import MRCat
+
+
+def test_MRCat_inputs():
+    input_map = dict(
+        args=dict(
+            argstr="%s",
+        ),
+        axis=dict(
+            argstr="-axis %s",
+        ),
+        bval_scale=dict(
+            argstr="-bvalue_scaling %s",
+        ),
+        datatype=dict(
+            argstr="-datatype %s",
+        ),
+        environ=dict(
+            nohash=True,
+            usedefault=True,
+        ),
+        grad_file=dict(
+            argstr="-grad %s",
+            extensions=None,
+            xor=["grad_fsl"],
+        ),
+        grad_fsl=dict(
+            argstr="-fslgrad %s %s",
+            xor=["grad_file"],
+        ),
+        in_bval=dict(
+            extensions=None,
+        ),
+        in_bvec=dict(
+            argstr="-fslgrad %s %s",
+            extensions=None,
+        ),
+        in_files=dict(
+            argstr="%s",
+            mandatory=True,
+            position=-2,
+        ),
+        nthreads=dict(
+            argstr="-nthreads %d",
+            nohash=True,
+        ),
+        out_file=dict(
+            argstr="%s",
+            extensions=None,
+            mandatory=True,
+            position=-1,
+            usedefault=True,
+        ),
+    )
+    inputs = MRCat.input_spec()
+
+    for key, metadata in list(input_map.items()):
+        for metakey, value in list(metadata.items()):
+            assert getattr(inputs.traits()[key], metakey) == value
+
+
+def test_MRCat_outputs():
+    output_map = dict(
+        out_file=dict(
+            extensions=None,
+        ),
+    )
+    outputs = MRCat.output_spec()
+
+    for key, metadata in list(output_map.items()):
+        for metakey, value in list(metadata.items()):
+            assert getattr(outputs.traits()[key], metakey) == value
diff --git a/nipype/interfaces/mrtrix3/utils.py b/nipype/interfaces/mrtrix3/utils.py
index 77c3047f20..fa624fa79c 100644
--- a/nipype/interfaces/mrtrix3/utils.py
+++ b/nipype/interfaces/mrtrix3/utils.py
@@ -64,9 +64,108 @@ def _list_outputs(self):
         return outputs
 
 
+class MRCatInputSpec(MRTrix3BaseInputSpec):
+    in_files = traits.List(
+        File(exists=True),
+        argstr="%s",
+        position=-2,
+        mandatory=True,
+        desc="files to concatenate",
+    )
+
+    out_file = File(
+        "concatenated.mif",
+        argstr="%s",
+        mandatory=True,
+        position=-1,
+        usedefault=True,
+        desc="output concatenated image",
+    )
+
+    axis = traits.Int(
+        argstr="-axis %s",
+        desc="""specify axis along which concatenation should be performed. By default,
+     the program will use the last non-singleton, non-spatial axis of any of
+     the input images - in other words axis 3 or whichever axis (greater than
+     3) of the input images has size greater than one""",
+    )
+
+    datatype = traits.Enum(
+        "float32",
+        "float32le",
+        "float32be",
+        "float64",
+        "float64le",
+        "float64be",
+        "int64",
+        "uint64",
+        "int64le",
+        "uint64le",
+        "int64be",
+        "uint64be",
+        "int32",
+        "uint32",
+        "int32le",
+        "uint32le",
+        "int32be",
+        "uint32be",
+        "int16",
+        "uint16",
+        "int16le",
+        "uint16le",
+        "int16be",
+        "uint16be",
+        "cfloat32",
+        "cfloat32le",
+        "cfloat32be",
+        "cfloat64",
+        "cfloat64le",
+        "cfloat64be",
+        "int8",
+        "uint8",
+        "bit",
+        argstr="-datatype %s",
+        desc="specify output image data type",
+    )
+
+
+class MRCatOutputSpec(TraitedSpec):
+    out_file = File(exists=True, desc="the output concatenated image")
+
+
+class MRCat(CommandLine):
+    """
+    Concatenate several images into one
+
+
+    Example
+    -------
+
+    >>> import nipype.interfaces.mrtrix3 as mrt
+    >>> mrcat = mrt.MRCat()
+    >>> mrcat.inputs.in_files = ['image1.mif','image2.mif']
+    >>> mrcat.cmdline                               # doctest: +ELLIPSIS
+    'mrcat image1.mif image2.mif concatenated.mif'
+    >>> mrcat.run()                                 # doctest: +SKIP
+    """
+
+    _cmd = "mrcat"
+    input_spec = MRCatInputSpec
+    output_spec = MRCatOutputSpec
+
+    def _list_outputs(self):
+        outputs = self.output_spec().get()
+        outputs["out_file"] = op.abspath(self.inputs.out_file)
+        return outputs
+
+
 class Mesh2PVEInputSpec(CommandLineInputSpec):
     in_file = File(
-        exists=True, argstr="%s", mandatory=True, position=-3, desc="input mesh"
+        exists=True,
+        argstr="%s",
+        mandatory=True,
+        position=-3,
+        desc="input mesh",
     )
     reference = File(
         exists=True,
@@ -134,7 +233,11 @@ class Generate5ttInputSpec(MRTrix3BaseInputSpec):
         desc="tissue segmentation algorithm",
     )
     in_file = File(
-        exists=True, argstr="%s", mandatory=True, position=-2, desc="input image"
+        exists=True,
+        argstr="%s",
+        mandatory=True,
+        position=-2,
+        desc="input image",
     )
     out_file = File(argstr="%s", mandatory=True, position=-1, desc="output image")
 
@@ -173,7 +276,11 @@ def _list_outputs(self):
 
 class TensorMetricsInputSpec(CommandLineInputSpec):
     in_file = File(
-        exists=True, argstr="%s", mandatory=True, position=-1, desc="input DTI image"
+        exists=True,
+        argstr="%s",
+        mandatory=True,
+        position=-1,
+        desc="input DTI image",
     )
 
     out_fa = File(argstr="-fa %s", desc="output FA file")
@@ -246,10 +353,18 @@ def _list_outputs(self):
 
 class ComputeTDIInputSpec(CommandLineInputSpec):
     in_file = File(
-        exists=True, argstr="%s", mandatory=True, position=-2, desc="input tractography"
+        exists=True,
+        argstr="%s",
+        mandatory=True,
+        position=-2,
+        desc="input tractography",
     )
     out_file = File(
-        "tdi.mif", argstr="%s", usedefault=True, position=-1, desc="output TDI file"
+        "tdi.mif",
+        argstr="%s",
+        usedefault=True,
+        position=-1,
+        desc="output TDI file",
     )
     reference = File(
         exists=True,
@@ -353,7 +468,8 @@ class ComputeTDIInputSpec(CommandLineInputSpec):
         "(these lengths are then taken into account during TWI calculation)",
     )
     ends_only = traits.Bool(
-        argstr="-ends_only", desc="only map the streamline" " endpoints to the image"
+        argstr="-ends_only",
+        desc="only map the streamline" " endpoints to the image",
     )
 
     tck_weights = File(
@@ -438,10 +554,18 @@ def _list_outputs(self):
 
 class TCK2VTKInputSpec(CommandLineInputSpec):
     in_file = File(
-        exists=True, argstr="%s", mandatory=True, position=-2, desc="input tractography"
+        exists=True,
+        argstr="%s",
+        mandatory=True,
+        position=-2,
+        desc="input tractography",
     )
     out_file = File(
-        "tracks.vtk", argstr="%s", usedefault=True, position=-1, desc="output VTK file"
+        "tracks.vtk",
+        argstr="%s",
+        usedefault=True,
+        position=-1,
+        desc="output VTK file",
     )
     reference = File(
         exists=True,
@@ -498,7 +622,11 @@ def _list_outputs(self):
 
 class DWIExtractInputSpec(MRTrix3BaseInputSpec):
     in_file = File(
-        exists=True, argstr="%s", mandatory=True, position=-2, desc="input image"
+        exists=True,
+        argstr="%s",
+        mandatory=True,
+        position=-2,
+        desc="input image",
     )
     out_file = File(argstr="%s", mandatory=True, position=-1, desc="output image")
     bzero = traits.Bool(argstr="-bzero", desc="extract b=0 volumes")
@@ -549,7 +677,11 @@ def _list_outputs(self):
 
 class MRConvertInputSpec(MRTrix3BaseInputSpec):
     in_file = File(
-        exists=True, argstr="%s", mandatory=True, position=-2, desc="input image"
+        exists=True,
+        argstr="%s",
+        mandatory=True,
+        position=-2,
+        desc="input image",
     )
     out_file = File(
         "dwi.mif",
@@ -566,7 +698,10 @@ class MRConvertInputSpec(MRTrix3BaseInputSpec):
         desc="extract data at the specified coordinates",
     )
     vox = traits.List(
-        traits.Float, sep=",", argstr="-vox %s", desc="change the voxel dimensions"
+        traits.Float,
+        sep=",",
+        argstr="-vox %s",
+        desc="change the voxel dimensions",
     )
     axes = traits.List(
         traits.Int,
@@ -615,7 +750,11 @@ def _list_outputs(self):
 
 class MRMathInputSpec(MRTrix3BaseInputSpec):
     in_file = File(
-        exists=True, argstr="%s", mandatory=True, position=-3, desc="input image"
+        exists=True,
+        argstr="%s",
+        mandatory=True,
+        position=-3,
+        desc="input image",
     )
     out_file = File(argstr="%s", mandatory=True, position=-1, desc="output image")
     operation = traits.Enum(
@@ -637,7 +776,9 @@ class MRMathInputSpec(MRTrix3BaseInputSpec):
         desc="operation to computer along a specified axis",
     )
     axis = traits.Int(
-        0, argstr="-axis %d", desc="specfied axis to perform the operation along"
+        0,
+        argstr="-axis %d",
+        desc="specfied axis to perform the operation along",
     )
 
 
@@ -677,7 +818,11 @@ def _list_outputs(self):
 
 class MRResizeInputSpec(MRTrix3BaseInputSpec):
     in_file = File(
-        exists=True, argstr="%s", position=-2, mandatory=True, desc="input DWI image"
+        exists=True,
+        argstr="%s",
+        position=-2,
+        mandatory=True,
+        desc="input DWI image",
     )
     image_size = traits.Tuple(
         (traits.Int, traits.Int, traits.Int),
diff --git a/tools/checkspecs.py b/tools/checkspecs.py
index 032fd122cc..7aaac0d107 100644
--- a/tools/checkspecs.py
+++ b/tools/checkspecs.py
@@ -13,8 +13,7 @@
 
 # Functions and classes
 class InterfaceChecker(object):
-    """Class for checking all interface specifications
-    """
+    """Class for checking all interface specifications"""
 
     def __init__(
         self,
@@ -23,7 +22,7 @@ def __init__(
         module_skip_patterns=None,
         class_skip_patterns=None,
     ):
-        r""" Initialize package for parsing
+        r"""Initialize package for parsing
 
         Parameters
         ----------
@@ -113,14 +112,14 @@ def _uri2path(self, uri):
         return path
 
     def _path2uri(self, dirpath):
-        """ Convert directory path to uri """
+        """Convert directory path to uri"""
         relpath = dirpath.replace(self.root_path, self.package_name)
         if relpath.startswith(os.path.sep):
             relpath = relpath[1:]
         return relpath.replace(os.path.sep, ".")
 
     def _parse_module(self, uri):
-        """ Parse module defined in *uri* """
+        """Parse module defined in *uri*"""
         filename = self._uri2path(uri)
         if filename is None:
             # nothing that we could handle here.
@@ -131,7 +130,7 @@ def _parse_module(self, uri):
         return functions, classes
 
     def _parse_lines(self, linesource, module):
-        """ Parse lines of text for functions and classes """
+        """Parse lines of text for functions and classes"""
         functions = []
         classes = []
         for line in linesource:
@@ -387,7 +386,7 @@ def test_specs(self, uri):
         return bad_specs
 
     def _survives_exclude(self, matchstr, match_type):
-        """ Returns True if *matchstr* does not match patterns
+        """Returns True if *matchstr* does not match patterns
 
         ``self.package_name`` removed from front of string if present
 
@@ -429,7 +428,7 @@ def _survives_exclude(self, matchstr, match_type):
         return True
 
     def discover_modules(self):
-        """ Return module sequence discovered from ``self.package_name``
+        """Return module sequence discovered from ``self.package_name``
 
 
         Parameters
diff --git a/tools/gitwash_dumper.py b/tools/gitwash_dumper.py
index 36efd7f83e..2c08547bac 100755
--- a/tools/gitwash_dumper.py
+++ b/tools/gitwash_dumper.py
@@ -50,9 +50,7 @@ def cp_files(in_path, globs, out_path):
 
 
 def filename_search_replace(sr_pairs, filename, backup=False):
-    """ Search and replace for expressions in files
-
-    """
+    """Search and replace for expressions in files"""
     in_txt = open(filename, "rt").read(-1)
     out_txt = in_txt[:]
     for in_exp, out_exp in sr_pairs:
@@ -94,7 +92,7 @@ def make_link_targets(
     url=None,
     ml_url=None,
 ):
-    """ Check and make link targets
+    """Check and make link targets
 
     If url is None or ml_url is None, check if there are links present for
     these in `known_link_fname`.  If not, raise error.  The check is:
diff --git a/tools/run_examples.py b/tools/run_examples.py
index 20382ef74d..bd77f1a0a4 100644
--- a/tools/run_examples.py
+++ b/tools/run_examples.py
@@ -4,9 +4,15 @@
 
 
 if __name__ == "__main__":
-    print(dedent("""Nipype examples have been moved to niflow-nipype1-examples.
+    print(
+        dedent(
+            """Nipype examples have been moved to niflow-nipype1-examples.
 
-Install with: pip install niflow-nipype1-examples"""))
+Install with: pip install niflow-nipype1-examples"""
+        )
+    )
     if sys.argv[1:]:
-        print("Run this command with: niflow-nipype1-examples " + " ".join(sys.argv[1:]))
+        print(
+            "Run this command with: niflow-nipype1-examples " + " ".join(sys.argv[1:])
+        )
     sys.exit(1)
diff --git a/tools/toollib.py b/tools/toollib.py
index 77d864f142..e740787575 100644
--- a/tools/toollib.py
+++ b/tools/toollib.py
@@ -31,7 +31,9 @@ def sh(cmd):
 def compile_tree():
     """Compile all Python files below current directory."""
     vstr = ".".join(map(str, sys.version_info[:2]))
-    stat = os.system("%s %s/lib/python%s/compileall.py ." % (sys.executable, sys.prefix, vstr))
+    stat = os.system(
+        "%s %s/lib/python%s/compileall.py ." % (sys.executable, sys.prefix, vstr)
+    )
     if stat:
         msg = "*** ERROR: Some Python files in tree do NOT compile! ***\n"
         msg += "See messages above for the actual file that produced it.\n"