cmd2 strives to be drop-in compatible with cmd, however there are a few incompatibilities.


The Cmd.emptyline() function is called when an empty line is entered in response to the prompt. By default, in cmd if this method is not overridden, it repeats and executes the last nonempty command entered. However, no end user we have encountered views this as expected or desirable default behavior. cmd2 completely ignores empty lines and the base class cmd.emptyline() method never gets called and thus the empty line behavior cannot be overridden.


In cmd, the Cmd.identchars attribute contains the string of characters accepted for command names. cmd uses those characters to split the first “word” of the input, without requiring the user to type a space. For example, if identchars contained a string of all alphabetic characters, the user could enter a command like L20 and it would be interpreted as the command L with the first argument of 20.

Since version 0.9.0, cmd2 has ignored identchars; the parsing logic in cmd2 splits the command and arguments on whitespace. We opted for this breaking change because while cmd supports unicode, using non-ascii unicode characters in command names while simultaneously using identchars functionality can be somewhat painful. Requiring white space to delimit arguments also ensures reliable operation of many other useful cmd2 features, including Completion and Shortcuts, Aliases, and Macros.

If you really need this functionality in your app, you can add it back in by writing a Postparsing Hook.


In cmd, the Cmd.cmdqueue attribute contains a list of queued input lines. The cmdqueue list is checked in cmdloop() when new input is needed; if it is nonempty, its elements will be processed in order, as if entered at the prompt.

Since version 0.9.13 cmd2 has removed support for Cmd.cmdqueue. Because cmd2 supports running commands via the main cmdloop(), text scripts, Python scripts, transcripts, and history replays, the only way to preserve consistent behavior across these methods was to eliminate the command queue. Additionally, reasoning about application behavior is much easier without this queue present.