Coding a shell in Python

Question

I am coding a data entry system in Python, in which the user should also be able to submit 'commands', exactly like the Python shell works, or for example SAS or R interfaces. I would like to know how to code a shell. For examnple, it should provide a prompt (which cannot be deleted by the user, e.g. the >>> prompt in Python) and receive input from the user. Furthermore, once an entry is submitted, the user cannot go back, like in the DOS prompt, where you cannot go up a line, so to speak.

Can anybody help with this?

Jeff LaFay · Accepted Answer · 2011-11-09 16:59:06Z

5

The cmd.Cmd class is something that would help you build a shell-like application. Likewise, cmd2 is a nice upgrade from the above module. With these you can build a shell application that has command history, help menus, and smart command parsing. Don't build a REPL from scratch because these modules will probably suffice for your needs.

edited Nov 9, 2011 at 16:59

answered Nov 9, 2011 at 16:48

Jeff LaFay

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2 Comments

Jeff LaFay Over a year ago

@Josh Lee, yes it does have some nice enhancements. I'll edit my answer to include cmd2 as well.

MiddleClassMan Over a year ago

Brilliant, thanks very much for putting me on the right track. Will try it out tonight!

Blender · Accepted Answer · 2011-11-09 16:47:57Z

0

I coded a whole sh implementation in Python a while back, but sadly I don't have the source.

Your basic code would be this:

while True:
  command = raw_input('>>> ')
  print 'You entered "{command}".'.format(command = command)

But if you need something more complicated than a simple bash-like shell, there are a few projects that might suit your needs:

IPython: Pretty solid shell. It's used by Sage and a bunch of other big projects.
Python's native cmd class: self explanatory. Not very feature rich, but it's the Python shell.

answered Nov 9, 2011 at 16:47

Blender

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8 Comments

Spencer Rathbun Over a year ago

You did? Did it also use vt100 control chars?

Blender Over a year ago

Go easy on me. I coded the features that I actually used, which was enough of an implementation for me.

Spencer Rathbun Over a year ago

I only ask because I'm usually coding on windoze boxes, where the shell is lousy. Since I can't find a decent replacement that is more of a "first class citizen" than interix or cygwin, I've decided to write a python one. With a little help from termEmulator I can get away from the terrible terminal too.

JS. Over a year ago

@Spencer: Have you tried the console application recommended by IPython? ipython.org/ipython-doc/stable/install/install.html and search for "console" It's not perfect, but you might find it useful.

Spencer Rathbun Over a year ago

@JS. yep, and it's fantastic at what it does. Which doesn't fit what I want, namely, a bash clone with features stolen from fish and msfconsole. Ipython is a python interpreter with shell convenience features. I'm coming from a different direction, and while I could probably get ipython to do what I want, I think it would be a fun project to work on.

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themel · Accepted Answer · 2011-11-09 16:50:33Z

0

You might want to look into the readline library (gets you fancy features like completion and history as well). Sadly, it's UNIX only, like it's underlying C library.

answered Nov 9, 2011 at 16:50

themel

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1 Comment

MiddleClassMan Over a year ago

Windows based here. Thanks anyway for the response!

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