What's the PowerShell syntax for multiple values in a switch statement?

switch($someString.ToLower()) 
{ 
    {($_ -eq "y") -or ($_ -eq "yes")} { "You entered Yes." } 
    default { "You entered No." } 
}

I found that this works and seems more readable:

switch($someString)
{
    { @("y", "yes") -contains $_ } { "You entered Yes." }
    default { "You entered No." }
}

The "-contains" operator performs a non-case sensitive search, so you don't need to use "ToLower()". If you do want it to be case sensitive, you can use "-ccontains" instead.

You should be able to use a wildcard for your values:

switch -wildcard ($someString.ToLower())
{
    "y*" { "You entered Yes." }
    default { "You entered No." }
}

Regular expressions are also allowed.

switch -regex ($someString.ToLower())
{
    "y(es)?" { "You entered Yes." }
    default { "You entered No." }
}

PowerShell switch documentation: Using the Switch Statement