Tuesday, May 04, 2010

PowerShell 2 Breaking Change When Shelling Out

Whilst PowerShell 2 is by-and-large backwards compatible, I’ve discovered at least one breaking change that appears to be undocumented: the behaviour of argument parsing when calling another executable seems to have changed.

Previous behaviour:


PowerShell has effectively parsed the argument as if it were calling a PowerShell script: splitting it into two parts along the colon, and passing the second part ‘intact’ because it was quote wrapped.

New behaviour in v2:


PowerShell has treated the arguments as completely opaque and passed them to the exe using ‘normal’ command line parsing semantics (split on spaces etc…). It has not split the argument along the colon (which was the breaking change for us). In the second case, because the argument didn’t start with a quote (it starts with ‘-test’) the argument is broken in half at the space.

I think this is a good change, in that PowerShell shouldn’t make assumptions about how the exe you are calling likes it’s parameters (I got badly burnt that way trying to call an SSIS package). But it’s certainly one to watch out for.


PS: Not sure at all about this behaviour, which is the same in both v1 and v2:


Surely the fact you pass the argument as a string variable indicates you want it as one argument. Surely.

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