lib/gen_cmd.py

#!/usr/bin/env python

r"""
This module provides command execution functions such as cmd_fnc and cmd_fnc_u.
"""

import os
import sys
import subprocess
import collections
import signal
import time
import re
import inspect

import gen_print as gp
import gen_valid as gv
import gen_misc as gm
import func_args as fa

robot_env = gp.robot_env

if robot_env:
    from robot.libraries.BuiltIn import BuiltIn


# cmd_fnc and cmd_fnc_u should now be considered deprecated.  shell_cmd and t_shell_cmd should be used
# instead.
def cmd_fnc(cmd_buf,
            quiet=None,
            test_mode=None,
            debug=0,
            print_output=1,
            show_err=1,
            return_stderr=0,
            ignore_err=1):
    r"""
    Run the given command in a shell and return the shell return code and the output.

    Description of arguments:
    cmd_buf                         The command string to be run in a shell.
    quiet                           Indicates whether this function should run the print_issuing() function
                                    which prints "Issuing: <cmd string>" to stdout.
    test_mode                       If test_mode is set, this function will not actually run the command.  If
                                    print_output is set, it will print "(test_mode) Issuing: <cmd string>" to
                                    stdout.
    debug                           If debug is set, this function will print extra debug info.
    print_output                    If this is set, this function will print the stdout/stderr generated by
                                    the shell command.
    show_err                        If show_err is set, this function will print a standardized error report
                                    if the shell command returns non-zero.
    return_stderr                   If return_stderr is set, this function will process the stdout and stderr
                                    streams from the shell command separately.  It will also return stderr in
                                    addition to the return code and the stdout.
    """

    # Determine default values.
    quiet = int(gm.global_default(quiet, 0))
    test_mode = int(gm.global_default(test_mode, 0))

    if debug:
        gp.print_vars(cmd_buf, quiet, test_mode, debug)

    err_msg = gv.valid_value(cmd_buf)
    if err_msg != "":
        raise ValueError(err_msg)

    if not quiet:
        gp.pissuing(cmd_buf, test_mode)

    if test_mode:
        if return_stderr:
            return 0, "", ""
        else:
            return 0, ""

    if return_stderr:
        err_buf = ""
        stderr = subprocess.PIPE
    else:
        stderr = subprocess.STDOUT

    sub_proc = subprocess.Popen(cmd_buf,
                                bufsize=1,
                                shell=True,
                                executable='/bin/bash',
                                stdout=subprocess.PIPE,
                                stderr=stderr)
    out_buf = ""
    if return_stderr:
        for line in sub_proc.stderr:
            try:
                err_buf += line
            except TypeError:
                line = line.decode("utf-8")
                err_buf += line
            if not print_output:
                continue
            gp.gp_print(line)
    for line in sub_proc.stdout:
        try:
            out_buf += line
        except TypeError:
            line = line.decode("utf-8")
            out_buf += line
        if not print_output:
            continue
        gp.gp_print(line)
    if print_output and not robot_env:
        sys.stdout.flush()
    sub_proc.communicate()
    shell_rc = sub_proc.returncode
    if shell_rc != 0:
        err_msg = "The prior shell command failed.\n"
        err_msg += gp.sprint_var(shell_rc, gp.hexa())
        if not print_output:
            err_msg += "out_buf:\n" + out_buf

        if show_err:
            gp.print_error_report(err_msg)
        if not ignore_err:
            if robot_env:
                BuiltIn().fail(err_msg)
            else:
                raise ValueError(err_msg)

    if return_stderr:
        return shell_rc, out_buf, err_buf
    else:
        return shell_rc, out_buf


def cmd_fnc_u(cmd_buf,
              quiet=None,
              debug=None,
              print_output=1,
              show_err=1,
              return_stderr=0,
              ignore_err=1):
    r"""
    Call cmd_fnc with test_mode=0.  See cmd_fnc (above) for details.

    Note the "u" in "cmd_fnc_u" stands for "unconditional".
    """

    return cmd_fnc(cmd_buf, test_mode=0, quiet=quiet, debug=debug,
                   print_output=print_output, show_err=show_err,
                   return_stderr=return_stderr, ignore_err=ignore_err)


def parse_command_string(command_string):
    r"""
    Parse a bash command-line command string and return the result as a dictionary of parms.

    This can be useful for answering questions like "What did the user specify as the value for parm x in the
    command string?".

    This function expects the command string to follow the following posix conventions:
    - Short parameters:
      -<parm name><space><arg value>
    - Long parameters:
      --<parm name>=<arg value>

    The first item in the string will be considered to be the command.  All values not conforming to the
    specifications above will be considered positional parms.  If there are multiple parms with the same
    name, they will be put into a list (see illustration below where "-v" is specified multiple times).

    Description of argument(s):
    command_string                  The complete command string including all parameters and arguments.

    Sample input:

    robot_cmd_buf:                                    robot -v OPENBMC_HOST:dummy1 -v keyword_string:'Set
    Auto Reboot  no' -v lib_file_path:/home/user1/git/openbmc-test-automation/lib/utils.robot -v quiet:0 -v
    test_mode:0 -v debug:0 --outputdir='/home/user1/status/children/'
    --output=dummy1.Auto_reboot.170802.124544.output.xml --log=dummy1.Auto_reboot.170802.124544.log.html
    --report=dummy1.Auto_reboot.170802.124544.report.html
    /home/user1/git/openbmc-test-automation/extended/run_keyword.robot

    Sample output:

    robot_cmd_buf_dict:
      robot_cmd_buf_dict[command]:                    robot
      robot_cmd_buf_dict[v]:
        robot_cmd_buf_dict[v][0]:                     OPENBMC_HOST:dummy1
        robot_cmd_buf_dict[v][1]:                     keyword_string:Set Auto Reboot no
        robot_cmd_buf_dict[v][2]:
        lib_file_path:/home/user1/git/openbmc-test-automation/lib/utils.robot
        robot_cmd_buf_dict[v][3]:                     quiet:0
        robot_cmd_buf_dict[v][4]:                     test_mode:0
        robot_cmd_buf_dict[v][5]:                     debug:0
      robot_cmd_buf_dict[outputdir]:                  /home/user1/status/children/
      robot_cmd_buf_dict[output]:                     dummy1.Auto_reboot.170802.124544.output.xml
      robot_cmd_buf_dict[log]:                        dummy1.Auto_reboot.170802.124544.log.html
      robot_cmd_buf_dict[report]:                     dummy1.Auto_reboot.170802.124544.report.html
      robot_cmd_buf_dict[positional]:
      /home/user1/git/openbmc-test-automation/extended/run_keyword.robot
    """

    # We want the parms in the string broken down the way bash would do it, so we'll call upon bash to do
    # that by creating a simple inline bash function.
    bash_func_def = "function parse { for parm in \"${@}\" ; do" +\
        " echo $parm ; done ; }"

    rc, outbuf = cmd_fnc_u(bash_func_def + " ; parse " + command_string,
                           quiet=1, print_output=0)
    command_string_list = outbuf.rstrip("\n").split("\n")

    command_string_dict = collections.OrderedDict()
    ix = 1
    command_string_dict['command'] = command_string_list[0]
    while ix < len(command_string_list):
        if command_string_list[ix].startswith("--"):
            key, value = command_string_list[ix].split("=")
            key = key.lstrip("-")
        elif command_string_list[ix].startswith("-"):
            key = command_string_list[ix].lstrip("-")
            ix += 1
            try:
                value = command_string_list[ix]
            except IndexError:
                value = ""
        else:
            key = 'positional'
            value = command_string_list[ix]
        if key in command_string_dict:
            if isinstance(command_string_dict[key], str):
                command_string_dict[key] = [command_string_dict[key]]
            command_string_dict[key].append(value)
        else:
            command_string_dict[key] = value
        ix += 1

    return command_string_dict


# Save the original SIGALRM handler for later restoration by shell_cmd.
original_sigalrm_handler = signal.getsignal(signal.SIGALRM)


def shell_cmd_timed_out(signal_number,
                        frame):
    r"""
    Handle an alarm signal generated during the shell_cmd function.
    """

    gp.dprint_executing()
    global command_timed_out
    command_timed_out = True
    # Get subprocess pid from shell_cmd's call stack.
    sub_proc = gp.get_stack_var('sub_proc', 0)
    pid = sub_proc.pid
    gp.dprint_var(pid)
    # Terminate the child process group.
    os.killpg(pid, signal.SIGKILL)
    # Restore the original SIGALRM handler.
    signal.signal(signal.SIGALRM, original_sigalrm_handler)

    return


def shell_cmd(command_string,
              quiet=None,
              print_output=None,
              show_err=1,
              test_mode=0,
              time_out=None,
              max_attempts=1,
              retry_sleep_time=5,
              valid_rcs=[0],
              ignore_err=None,
              return_stderr=0,
              fork=0,
              error_regexes=None):
    r"""
    Run the given command string in a shell and return a tuple consisting of the shell return code and the
    output.

    Description of argument(s):
    command_string                  The command string to be run in a shell (e.g. "ls /tmp").
    quiet                           If set to 0, this function will print "Issuing: <cmd string>" to stdout.
                                    When the quiet argument is set to None, this function will assign a
                                    default value by searching upward in the stack for the quiet variable
                                    value.  If no such value is found, quiet is set to 0.
    print_output                    If this is set, this function will print the stdout/stderr generated by
                                    the shell command to stdout.
    show_err                        If show_err is set, this function will print a standardized error report
                                    if the shell command fails (i.e. if the shell command returns a shell_rc
                                    that is not in valid_rcs).  Note: Error text is only printed if ALL
                                    attempts to run the command_string fail.  In other words, if the command
                                    execution is ultimately successful, initial failures are hidden.
    test_mode                       If test_mode is set, this function will not actually run the command.  If
                                    print_output is also set, this function will print "(test_mode) Issuing:
                                    <cmd string>" to stdout.  A caller should call shell_cmd directly if they
                                    wish to have the command string run unconditionally.  They should call
                                    the t_shell_cmd wrapper (defined below) if they wish to run the command
                                    string only if the prevailing test_mode variable is set to 0.
    time_out                        A time-out value expressed in seconds.  If the command string has not
                                    finished executing within <time_out> seconds, it will be halted and
                                    counted as an error.
    max_attempts                    The max number of attempts that should be made to run the command string.
    retry_sleep_time                The number of seconds to sleep between attempts.
    valid_rcs                       A list of integers indicating which shell_rc values are not to be
                                    considered errors.
    ignore_err                      Ignore error means that a failure encountered by running the command
                                    string will not be raised as a python exception.  When the ignore_err
                                    argument is set to None, this function will assign a default value by
                                    searching upward in the stack for the ignore_err variable value.  If no
                                    such value is found, ignore_err is set to 1.
    return_stderr                   If return_stderr is set, this function will process the stdout and stderr
                                    streams from the shell command separately.  In such a case, the tuple
                                    returned by this function will consist of three values rather than just
                                    two: rc, stdout, stderr.
    fork                            Run the command string asynchronously (i.e. don't wait for status of the
                                    child process and don't try to get stdout/stderr) and return the Popen
                                    object created by the subprocess.popen() function.  See the kill_cmd
                                    function for details on how to process the popen object.
    error_regexes                   A list of regular expressions to be used to identify errors in the
                                    command output.  If there is a match for any of these regular
                                    expressions, the command will be considered a failure and the shell_rc
                                    will be set to -1.  For example, if error_regexes = ['ERROR:'] and the
                                    command output contains 'ERROR:  Unrecognized option', it will be counted
                                    as an error even if the command returned 0.  This is useful when running
                                    commands that do not always return non-zero on error.
    """

    err_msg = gv.valid_value(command_string)
    if err_msg:
        raise ValueError(err_msg)

    # Assign default values to some of the arguments to this function.
    quiet = int(gm.dft(quiet, gp.get_stack_var('quiet', 0)))
    print_output = int(gm.dft(print_output, not quiet))
    show_err = int(show_err)
    ignore_err = int(gm.dft(ignore_err, gp.get_stack_var('ignore_err', 1)))

    gp.qprint_issuing(command_string, test_mode)
    if test_mode:
        return (0, "", "") if return_stderr else (0, "")

    # Convert a string python dictionary definition to a dictionary.
    valid_rcs = fa.source_to_object(valid_rcs)
    # Convert each list entry to a signed value.
    valid_rcs = [gm.to_signed(x) for x in valid_rcs]

    stderr = subprocess.PIPE if return_stderr else subprocess.STDOUT

    # Write all output to func_out_history_buf rather than directly to stdout.  This allows us to decide
    # what to print after all attempts to run the command string have been made.  func_out_history_buf will
    # contain the complete history from the current invocation of this function.
    global command_timed_out
    command_timed_out = False
    func_out_history_buf = ""
    for attempt_num in range(1, max_attempts + 1):
        sub_proc = subprocess.Popen(command_string,
                                    preexec_fn=os.setsid,
                                    bufsize=1,
                                    shell=True,
                                    universal_newlines=True,
                                    executable='/bin/bash',
                                    stdout=subprocess.PIPE,
                                    stderr=stderr)
        if fork:
            return sub_proc

        if time_out:
            command_timed_out = False
            # Designate a SIGALRM handling function and set alarm.
            signal.signal(signal.SIGALRM, shell_cmd_timed_out)
            signal.alarm(time_out)
        try:
            stdout_buf, stderr_buf = sub_proc.communicate()
        except IOError:
            command_timed_out = True
        # Restore the original SIGALRM handler and clear the alarm.
        signal.signal(signal.SIGALRM, original_sigalrm_handler)
        signal.alarm(0)

        # Output from this loop iteration is written to func_out_buf for later processing.  This can include
        # stdout, stderr and our own error messages.
        func_out_buf = ""
        if print_output:
            if return_stderr:
                func_out_buf += stderr_buf
            func_out_buf += stdout_buf
        shell_rc = sub_proc.returncode
        if shell_rc in valid_rcs:
            # Check output for text indicating there is an error.
            if error_regexes and re.match('|'.join(error_regexes), stdout_buf):
                shell_rc = -1
            else:
                break
        err_msg = "The prior shell command failed.\n"
        err_msg += gp.sprint_var(attempt_num)
        err_msg += gp.sprint_vars(command_string, command_timed_out, time_out)
        err_msg += gp.sprint_varx("child_pid", sub_proc.pid)
        err_msg += gp.sprint_vars(shell_rc, valid_rcs, fmt=gp.hexa())
        if error_regexes:
            err_msg += gp.sprint_vars(error_regexes)
        if not print_output:
            if return_stderr:
                err_msg += "stderr_buf:\n" + stderr_buf
            err_msg += "stdout_buf:\n" + stdout_buf
        if show_err:
            func_out_buf += gp.sprint_error_report(err_msg)
        if attempt_num < max_attempts:
            cmd_buf = "time.sleep(" + str(retry_sleep_time) + ")"
            if show_err:
                func_out_buf += gp.sprint_issuing(cmd_buf)
            exec(cmd_buf)
        func_out_history_buf += func_out_buf

    if shell_rc in valid_rcs:
        gp.gp_print(func_out_buf)
    else:
        if show_err:
            gp.gp_print(func_out_history_buf, stream='stderr')
        else:
            # There is no error information to show so just print output from last loop iteration.
            gp.gp_print(func_out_buf)
        if not ignore_err:
            # If the caller has already asked to show error info, avoid repeating that in the failure message.
            err_msg = "The prior shell command failed.\n" if show_err \
                else err_msg
            if robot_env:
                BuiltIn().fail(err_msg)
            else:
                raise ValueError(err_msg)

    return (shell_rc, stdout_buf, stderr_buf) if return_stderr \
        else (shell_rc, stdout_buf)


def t_shell_cmd(command_string, **kwargs):
    r"""
    Search upward in the the call stack to obtain the test_mode argument, add it to kwargs and then call
    shell_cmd and return the result.

    See shell_cmd prolog for details on all arguments.
    """

    if 'test_mode' in kwargs:
        error_message = "Programmer error - test_mode is not a valid" +\
            " argument to this function."
        gp.print_error_report(error_message)
        exit(1)

    test_mode = int(gp.get_stack_var('test_mode', 0))
    kwargs['test_mode'] = test_mode

    return shell_cmd(command_string, **kwargs)


def kill_cmd(popen, sig=signal.SIGTERM):
    r"""
    Kill the subprocess represented by the Popen object and return a tuple consisting of the shell return
    code and the output.

    This function is meant to be used as the follow-up for a call to shell_cmd(..., fork=1).

    Example:
    popen = shell_cmd("some_pgm.py", fork=1)
    ...
    shell_rc, output = kill_cmd(popen)

    Description of argument(s):
    popen                           A Popen object returned by the subprocess.Popen() command.
    sig                             The signal to be sent to the child process.
    """

    gp.dprint_var(popen.pid)
    os.killpg(popen.pid, sig)
    stdout, stderr = popen.communicate()
    shell_rc = popen.returncode
    return (shell_rc, stdout, stderr) if stderr else (shell_rc, stdout)


def re_order_kwargs(stack_frame_ix, **kwargs):
    r"""
    Re-order the kwargs to match the order in which they were specified on a function invocation and return
    as an ordered dictionary.

    Note that this re_order_kwargs function should not be necessary in python versions 3.6 and beyond.

    Example:

    The caller calls func1 like this:

    func1('mike', arg1='one', arg2='two', arg3='three')

    And func1 is defined as follows:

    def func1(first_arg, **kwargs):

        kwargs = re_order_kwargs(first_arg_num=2, stack_frame_ix=3, **kwargs)

    The kwargs dictionary before calling re_order_kwargs (where order is not guaranteed):

    kwargs:
      kwargs[arg3]:          three
      kwargs[arg2]:          two
      kwargs[arg1]:          one

    The kwargs dictionary after calling re_order_kwargs:

    kwargs:
      kwargs[arg1]:          one
      kwargs[arg2]:          two
      kwargs[arg3]:          three

    Note that the re-ordered kwargs match the order specified on the call to func1.

    Description of argument(s):
    stack_frame_ix                  The stack frame of the function whose kwargs values must be re-ordered.
                                    0 is the stack frame of re_order_kwargs, 1 is the stack from of its
                                    caller and so on.
    kwargs                          The keyword argument dictionary which is to be re-ordered.
    """

    new_kwargs = collections.OrderedDict()

    # Get position number of first keyword on the calling line of code.
    (args, varargs, keywords, locals) =\
        inspect.getargvalues(inspect.stack()[stack_frame_ix][0])
    first_kwarg_pos = 1 + len(args)
    if varargs is not None:
        first_kwarg_pos += len(locals[varargs])
    for arg_num in range(first_kwarg_pos, first_kwarg_pos + len(kwargs)):
        # This will result in an arg_name value such as "arg1='one'".
        arg_name = gp.get_arg_name(None, arg_num, stack_frame_ix + 2)
        # Continuing with the prior example, the following line will result
        # in key being set to 'arg1'.
        key = arg_name.split('=')[0]
        new_kwargs[key] = kwargs[key]

    return new_kwargs


def default_arg_delim(arg_dashes):
    r"""
    Return the default argument delimiter value for the given arg_dashes value.

    Note: this function is useful for functions that manipulate bash command line arguments (e.g. --parm=1 or
    -parm 1).

    Description of argument(s):
    arg_dashes                      The argument dashes specifier (usually, "-" or "--").
    """

    if arg_dashes == "--":
        return "="

    return " "


def create_command_string(command, *pos_parms, **options):
    r"""
    Create and return a bash command string consisting of the given arguments formatted as text.

    The default formatting of options is as follows:

    <single dash><option name><space delim><option value>

    Example:

    -parm value

    The caller can change the kind of dashes/delimiters used by specifying "arg_dashes" and/or "arg_delims"
    as options.  These options are processed specially by the create_command_string function and do NOT get
    inserted into the resulting command string.  All options following the arg_dashes/arg_delims options will
    then use the specified values for dashes/delims.  In the special case of arg_dashes equal to "--", the
    arg_delim will automatically be changed to "=".  See examples below.

    Quoting rules:

    The create_command_string function will single quote option values as needed to prevent bash expansion.
    If the caller wishes to defeat this action, they may single or double quote the option value themselves.
    See examples below.

    pos_parms are NOT automatically quoted.  The caller is advised to either explicitly add quotes or to use
    the quote_bash_parm functions to quote any pos_parms.

    Examples:

    command_string = create_command_string('cd', '~')

    Result:
    cd ~

    Note that the pos_parm ("~") does NOT get quoted, as per the aforementioned rules.  If quotes are
    desired, they may be added explicitly by the caller:

    command_string = create_command_string('cd', '\'~\'')

    Result:
    cd '~'

    command_string = create_command_string('grep', '\'^[^ ]*=\'',
        '/tmp/myfile', i=None, m='1', arg_dashes='--', color='always')

    Result:
    grep -i -m 1 --color=always '^[^ ]*=' /tmp/myfile

    In the preceding example, note the use of None to cause the "i" parm to be treated as a flag (i.e. no
    argument value is generated).  Also, note the use of arg_dashes to change the type of dashes used on all
    subsequent options.  The following example is equivalent to the prior.  Note that quote_bash_parm is used
    instead of including the quotes explicitly.

    command_string = create_command_string('grep', quote_bash_parm('^[^ ]*='),
        '/tmp/myfile', i=None,  m='1', arg_dashes='--', color='always')

    Result:
    grep -i -m 1 --color=always '^[^ ]*=' /tmp/myfile

    In the following example, note the automatic quoting of the password option, as per the aforementioned
    rules.

    command_string = create_command_string('my_pgm', '/tmp/myfile', i=None,
        m='1', arg_dashes='--', password='${my_pw}')

    However, let's say that the caller wishes to have bash expand the password value.  To achieve this, the
    caller can use double quotes:

    command_string = create_command_string('my_pgm', '/tmp/myfile', i=None,
        m='1', arg_dashes='--', password='"${my_pw}"')

    Result:
    my_pgm -i -m 1 --password="${my_pw}" /tmp/myfile

    command_string = create_command_string('ipmitool', 'power status',
        I='lanplus', C='3', U='root', P='0penBmc', H='wsbmc010')

    Result:
    ipmitool -I lanplus -C 3 -U root -P 0penBmc -H wsbmc010 power status

    By default create_command_string will take measures to preserve the order of the callers options.  In
    some cases, this effort may fail (as when calling directly from a robot program).  In this case, the
    caller can accept the responsibility of keeping an ordered list of options by calling this function with
    the last positional parm as some kind of dictionary (preferably an OrderedDict) and avoiding the use of
    any actual option args.

    Example:
    kwargs = collections.OrderedDict([('pass', 0), ('fail', 0)])
    command_string = create_command_string('my program', 'pos_parm1', kwargs)

    Result:

    my program -pass 0 -fail 0 pos_parm1

    Note to programmers who wish to write a wrapper to this function:  If the python version is less than
    3.6, to get the options to be processed correctly, the wrapper function must include a _stack_frame_ix_
    keyword argument to allow this function to properly re-order options:

    def create_ipmi_ext_command_string(command, **kwargs):

        return create_command_string('ipmitool', command, _stack_frame_ix_=2,
            **kwargs)

    Example call of wrapper function:

    command_string = create_ipmi_ext_command_string('power status', I='lanplus')

    Description of argument(s):
    command                         The command (e.g. "cat", "sort", "ipmitool", etc.).
    pos_parms                       The positional parms for the command (e.g. PATTERN, FILENAME, etc.).
                                    These will be placed at the end of the resulting command string.
    options                         The command options (e.g. "-m 1", "--max-count=NUM", etc.).  Note that if
                                    the value of any option is None, then it will be understood to be a flag
                                    (for which no value is required).
    """

    arg_dashes = "-"
    delim = default_arg_delim(arg_dashes)

    command_string = command

    if len(pos_parms) > 0 and gp.is_dict(pos_parms[-1]):
        # Convert pos_parms from tuple to list.
        pos_parms = list(pos_parms)
        # Re-assign options to be the last pos_parm value (which is a dictionary).
        options = pos_parms[-1]
        # Now delete the last pos_parm.
        del pos_parms[-1]
    else:
        # Either get stack_frame_ix from the caller via options or set it to the default value.
        stack_frame_ix = options.pop('_stack_frame_ix_', 1)
        if gm.python_version < gm.ordered_dict_version:
            # Re-establish the original options order as specified on the original line of code.  This
            # function depends on correct order.
            options = re_order_kwargs(stack_frame_ix, **options)
    for key, value in options.items():
        # Check for special values in options and process them.
        if key == "arg_dashes":
            arg_dashes = str(value)
            delim = default_arg_delim(arg_dashes)
            continue
        if key == "arg_delim":
            delim = str(value)
            continue
        # Format the options elements into the command string.
        command_string += " " + arg_dashes + key
        if value is not None:
            command_string += delim
            if re.match(r'^(["].*["]|[\'].*[\'])$', str(value)):
                # Already quoted.
                command_string += str(value)
            else:
                command_string += gm.quote_bash_parm(str(value))
    # Finally, append the pos_parms to the end of the command_string.  Use filter to eliminate blank pos
    # parms.
    command_string = ' '.join([command_string] + list(filter(None, pos_parms)))

    return command_string