Integrating with the OS

How to redirect output

See Output Redirection and Pipes

Executing OS commands from within cmd2

cmd2 includes a shell command which executes it’s arguments in the operating system shell:

(Cmd) shell ls -al

If you use the default Shortcuts defined in cmd2 you’ll get a ! shortcut for shell, which allows you to type:

(Cmd) !ls -al

NOTE: cmd2 provides user-friendly tab completion throughout the process of running a shell command - first for the shell command name itself, and then for file paths in the argument section.


cmd2 includes the built-in edit command which runs a text editor and optionally opens a file with it:

(Cmd) edit foo.txt

The editor used is determined by the editor settable parameter and can be either a text editor such as vim or a graphical editor such as VSCode. To set it:

set editor <program_name>

If you have the EDITOR environment variable set, then this will be the default value for editor. If not, then cmd2 will attempt to search for any in a list of common editors for your operating system.

Terminal pagers

Output of any command can be displayed one page at a time using the ppaged() method.

Alternatively, a terminal pager can be invoked directly using the ability to run shell commands with the ! shortcut like so:

(Cmd) !less foo.txt

NOTE: Once you are in a terminal pager, that program temporarily has control of your terminal, NOT cmd2. Typically you can use either the arrow keys or <PageUp>/<PageDown> keys to scroll around or type q to quit the pager and return control to your cmd2 application.

Exit codes

The self.exit_code attribute of your cmd2 application controls what exit code is returned from cmdloop() when it completes. It is your job to make sure that this exit code gets sent to the shell when your application exits by calling sys.exit(app.cmdloop()).

Invoking With Arguments

Typically you would invoke a cmd2 program by typing:

$ python



Either of these methods will launch your program and enter the cmd2 command loop, which allows the user to enter commands, which are then executed by your program.

You may want to execute commands in your program without prompting the user for any input. There are several ways you might accomplish this task. The easiest one is to pipe commands and their arguments into your program via standard input. You don’t need to do anything to your program in order to use this technique. Here’s a demonstration using the examples/ included in the source code of cmd2:

$ echo "speak -p some words" | python examples/
omesay ordsway

Using this same approach you could create a text file containing the commands you would like to run, one command per line in the file. Say your file was called somecmds.txt. To run the commands in the text file using your cmd2 program (from a Windows command prompt):

c:\cmd2> type somecmds.txt | python.exe examples/
omesay ordsway

By default, cmd2 programs also look for commands pass as arguments from the operating system shell, and execute those commands before entering the command loop:

$ python examples/ help

Documented commands (use 'help -v' for verbose/'help <topic>' for details):
alias  help     macro   orate  quit          run_script  set    shortcuts
edit   history  mumble  py     run_pyscript  say         shell  speak


You may need more control over command line arguments passed from the operating system shell. For example, you might have a command inside your cmd2 program which itself accepts arguments, and maybe even option strings. Say you wanted to run the speak command from the operating system shell, but have it say it in pig latin:

$ python example/ speak -p hello there
python speak -p hello there
usage: speak [-h] [-p] [-s] [-r REPEAT] words [words ...]
speak: error: the following arguments are required: words
*** Unknown syntax: -p
*** Unknown syntax: hello
*** Unknown syntax: there

Uh-oh, that’s not what we wanted. cmd2 treated -p, hello, and there as commands, which don’t exist in that program, thus the syntax errors.

There is an easy way around this, which is demonstrated in examples/ By setting allow_cli_args=False you can so your own argument parsing of the command line:

$ python examples/ speak -p hello there
ellohay heretay

Check the source code of this example, especially the main() function, to see the technique.

Alternatively you can simply wrap the command plus arguments in quotes (either single or double quotes):

$ python example/ "speak -p hello there"
ellohay heretay

Automating cmd2 apps from other CLI/CLU tools

While cmd2 is designed to create interactive command-line applications which enter a Read-Evaluate-Print-Loop (REPL), there are a great many times when it would be useful to use a cmd2 application as a run-and-done command-line utility for purposes of automation and scripting.

This is easily achieved by combining the following capabilities of cmd2:

  1. Ability to invoke a cmd2 application with arguments
  2. Ability to set an exit code when leaving a cmd2 application
  3. Ability to exit a cmd2 application with the quit command

Here is a simple example which doesn’t require the quit command since the custom exit command quits while returning an exit code:

$ python examples/ "exit 23"
'examples/' exiting with code: 23
$ echo $?

Here is another example using quit:

$ python example/ "speak -p hello there" quit
ellohay heretay