Determine if parameter is regular expression?

I have created a Powershell routine for setting mp3 tags on songs, where I'd like some of my parameters to act as either a regular expession or a "simple" string. To be specific, if the parameter can be said to work as a regular expression, the function should try to use this for retrieving its value; if it can't, it should simply use that value.

I've just browsed Parameter sets, and don't think this would suit me since I want to be flexible with the parameter handling; i.e. I'd like several parameters to act this way independently. But maybe I'm wrong in this? Anyway, help would be a开发者_如何转开发ppreciated.

You don't really need the try/catch if you use:

 IF ($string -as [regex])

If the cast is successful it will return the regex, if not it will return $null, so used as a boolean test in the IF, it will be $true if it is a valid regex, and $false if it is not.

That being said, the I'd agree with Joey that you should settle on a single match type (either wildcard or regex) and stick with that. There's too much potential for unintended consequences in trying to determine if a regex metacharacter was intended to be match literally or not.

You can try converting the string to a regular expression and look for failures. If there is an exception, just use it as string:

$isParamRegex = $(try { $null = [regex]$Param; $true } catch { $false })

As for the parameter type, just make it a string and document it appropriately.

However, I'd say you might want to go a different route there:

• Either make the argument always a regex, to avoid surprises with metacharacters.
• Or make it a pattern for -like instead of -match which is a bit more predictable for users (imho).
• In both cases provide a LiteralParam argument, akin to LiteralPath to just pass things as plain strings which are handled as such.