Since I started using Powershell, I’m very picky about what I let on my path. I feel it’s much cleaner to create aliases or functions rather than letting all kinds of crud creep into my path.
Recently, I installed the latest IronRuby release and discovered there’s a whole bunch of little batch file wrappers around common Ruby commands like gem and rake. While being able to simply type “igem” or “irake” is much easier than typing “ir "C:\Program Files\ironruby-0.6.0\bin\igem"”, I didn’t want to pollute my path - even with a product from my team. Instead, I wanted to create a Powershell function for each of those IronRuby-fied commands. Furthermore, I wanted to avoid manually creating a function for each Ruby command – these batchfiles are literally identical except for their name, so I figured it would be possible automate the function creation in Powershell. Here’s what I came up with:
I start by getting the ir alias, which I’m setting in my traditional fashion. The Ruby command files are in the same directory as ir.exe, which is what ir is aliased to. If the ir alias isn’t set, I quit out of the script without setting anything.
The make-rubyfunction function is the primary workhorse of this script. You pass in a command name as a string, and it uses set-item on the function provider to create a new function. Note, I had to explicitly create this function in the global scope since I’m running the set-item cmdlet inside a script.
Getting the value for the function took a bit of head banging to figure out. I’m used to Python, which automatically closes over variables, so my first attempt was to set the function value to something like { ir $cmdpath $args }. But Powershell doesn’t close automatically, so that fails since $cmd isn’t defined inside the function. I asked around on the internal Powershell alias, and someone pointed me to the new GetNewClosure function in Powershell v2. In other words, Powershell only supports manual closures, which is kind of wonky, but works OK for this scenario. I create a new script block that references in-scope variable $cmdpath and GetNewClosure automatically creates a new script block where that value is captured and embedded. More info on GetNewClosure in the docs.
Now, I’m using Win7 exclusively at this point, so depending on a v2 feature didn’t bother me. However, if you’re using Powershell v1, you could still accomplish something similar using text substitution. Here’s my original (i.e. pre-GetNewClosure) version of make-rubyfunction
I’m using Powershell’s standard text substitution mechanism to create the function value as a string. Note that I’m escaping the dollar sign in $args, so that does not get substituted the way $cmdpath does. GetNewClosure feels cleaner, so that’s how I ended up doing it, but both ways seem to work fine.
Finally, I pass an array of IronRuby commands down the pipe to make-rubyfunction. I love the pipe command, though it feels strange to use parentheses instead of square brackets for list comprehensions like Python and F#!
Anyway, the script – as usual – is up on my SkyDrive. At some point, I want to do something similar for common IronPython scripts like pyc and ipydbg. Until then, hopefully someone out there will find it useful (like maybe the IronRuby team?).
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