How can I see which options are available in a RegexOptions enum?

Question

How to use this function from powershell script to perform a case insensitive match with using the -cmatch operator:

static System.Text.RegularExpressions.Match Match(
     string input, 
     string pattern,
     System.Text.RegularExpressions.RegexOptions options)

I'm thinking its something like this:

PS>  $input = "one two three"

PS>  $m = [regex]::Match($input, "one", ????)

The part I have a question about is the ???? above.

How do you see what System.Text.RegularExpressions.RegexOptions are available from powershell prompt and what's the syntax to use it in the code above?

Answer 1

The easy "cheat" way to see what options are available in an enum is to use tab completion within the PowerShell prompt or ISE. Start with [System.Text.RegularExpressions.RegexOptions]:: and then use CTRL SPACE (or TAB) to see the options.

The programmatic way, since RegexOptions is an enum, is this:

[System.Enum]::GetNames([System.Text.RegularExpressions.RegexOptions])

When you need to pass enum values in PowerShell, you can pass the long-form fully-qualified enum value (this is my preference):

[System.Text.RegularExpressions.RegexOptions]::IgnoreCase

Or you can pass the numeric value directly (1), or you can pass a string and it will be matched to the enum's text value 'IgnoreCase'.

For your actual question: using [regex]::Match() is already case sensitive. You can just pass [System.Text.RegularExpressions.RegexOptions]::None to your call (or 0, or 'None').

If you want it to be case-insensitive, then you use the IgnoreCase enum value as above.

Because this type of enum is a series of bit flags, you can combine them. To do that you use the -bor (bitwise or, or binary or) operator:

$myOptions = [System.Text.RegularExpressions.RegexOptions]::IgnoreCase -bor 
        [System.Text.RegularExpressions.RegexOptions]::SingleLine -bor
        [System.Text.RegularExpressions.RegexOptions]::IgnorePatternWhitespace

But PowerShell's convenient coercion of strings to enums doesn't stop at single values. As mklement0 reminded me, you can comma separate the enum names within a string and PowerShell will still correctly parse it.

So you can use a string like 'IgnoreCase, SingleLine, IgnorePatternWhitespace' directly when you need to pass in RegexOptions. You can also pre-cast it:

$myOptions = 'IgnoreCase, SingleLine, IgnorePatternWhitespace' -as [System.Text.RegularExpressions.RegexOptions]
$myOptions = [System.Text.RegularExpressions.RegexOptions]'IgnoreCase, SingleLine, IgnorePatternWhitespace'

Answer 2

Simplifying braintist answer a little bit to use namespaces:

PS> using namespace System.Text.RegularExpressions

PS> [Enum]::GetNames([RegexOptions])
None
IgnoreCase
Multiline
ExplicitCapture
Compiled
Singleline
IgnorePatternWhitespace
RightToLeft
ECMAScript
CultureInvariant

PS>  $input = "one two three"

PS>  $m = [regex]::Match($input, "one", [RegexOptions]::IgnoreCase)