def command_list(self, sources, _opt=False):
        '''command line as list'''
        def abspath(x):
            x = Path(x).abspath()
            if not x.exists():
                raise ValueError('file not found! ' + x)
            return x

        self.f_cpu = int(self.f_cpu)

        self.mcu = str(self.mcu)
#        if not self.mcu  in self.targets:
#            raise ValueError('invalid mcu:' + self.mcu)

        if not _opt:
            sources = [abspath(x) for x in sources]
        includes = [abspath(x) for x in self.includes]

        if not self.output:
            self.output = tempfile.NamedTemporaryFile(
                prefix='pyavrutils_', suffix='.elf', delete=0).name

        defines = self.defines + ['F_CPU=' + str(self.f_cpu)]

        cmd = [self.cc]
        if not self.use_only_extra_options:
            if not _opt:
                cmd += sources
            cmd += ['-D' + x for x in defines]
            cmd += ['-I' + x for x in includes]
            if not _opt:
                cmd += ['-o', self.output]
            cmd += ['-mmcu=' + self.mcu]
            cmd += ['--std=' + self.std]
            if self.relax:
                cmd += ['-Wl,--relax']
            if self.gc_sections:
                cmd += ['-Wl,--gc-sections']
            if self.ffunction_sections:
                cmd += ['-ffunction-sections']
            if self.fdata_sections:
                cmd += ['-fdata-sections']
            if self.fno_inline_small_functions:
                cmd += ['-fno-inline-small-functions']
            if self.optimization != 0:
                cmd += ['-O' + str(self.optimization)]

        cmd += self.options_extra
        return cmd