Command history and completion for CLI

Introduction

Out of the box, the gaffer command line app gaffer cli isn't particularly useable - there's no tab-to-complete, history, or line editing. This is because the python module responsible for such things isn't compatible with the BSD license, and therefore can't be distributed with Gaffer. This short how-to provides a workaround for that.

Enabling readline and command completion

Chances are you already have a system install of python, and it has the readline module. If so, the following startup script will locate it and set it up, along with some nice tab-based completion. Just copy-paste the following code into a ~/gaffer/startup/cli/completion.py file:

import imp
import sys

# Import readline. First, try a normal import, and if that fails then 
# attempt to locate and import readline from a system-level install.
try :
        import readline
except ImportError :
        pythonVersion = ".".join( [ str( x ) for x in sys.version_info[:2] ] )
        f = imp.find_module( "readline", [ "/usr/lib/python%s/lib-dynload" % pythonVersion ] )
        readline = imp.load_module( "readline", *f )

# Bind tab as a completion trigger.
if "libedit" in readline.__doc__ :
        readline.parse_and_bind( "bind ^I rl_complete" )
else :
        readline.parse_and_bind( "tab: complete" )
        
# Register a custom completer that allows Tab to work for indentation
# as well as completion.

import rlcompleter
class __IndentingCompleter( rlcompleter.Completer ) :

        def complete( self, text, state ) :
        
                if not text or text.isspace() :
                        return "\t" if not state else None
                else :
                        return rlcompleter.Completer.complete( self, text, state )

readline.set_completer( __IndentingCompleter().complete )