Integrating with the OS

  • how to redirect output
  • executing OS commands from within cmd2
  • editors
  • paging
  • exit codes
  • Automation and calling cmd2 from other CLI/CLU tools via commands at invocation and quit

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 (type help <topic>):
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.