Integrating with the OS¶
How to redirect output¶
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.
Editors¶
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 mycmd2program.py
or:
$ mycmd2program.py
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/example.py
included in
the source code of cmd2
:
$ echo "speak -p some words" | python examples/example.py
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/example.py
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/example.py 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
(Cmd)
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/example.py speak -p hello there
python example.py 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
(Cmd)
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/cmd_as_argument.py
. By setting allow_cli_args=False
you can so
your own argument parsing of the command line:
$ python examples/cmd_as_argument.py 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/example.py "speak -p hello there"
ellohay heretay
(Cmd)
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
:
- Ability to invoke a
cmd2
application with arguments - Ability to set an exit code when leaving a
cmd2
application - Ability to exit a
cmd2
application with thequit
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_code.py "exit 23"
'examples/exit_code.py' exiting with code: 23
$ echo $?
23
Here is another example using quit
:
$ python example/example.py "speak -p hello there" quit
ellohay heretay
$