If you must ensure that a string contains only a given set of characters, try this:
$text = 'tobias.weltner' $hasOtherCharacters = $text -cmatch '[^a-zA-Z]' "$text has illegal characters? $hasOtherCharacters"
It is really simple: In the brackets, add the characters that are legal. Whenever PowerShell now finds a character in the string that is not in this list, you receive a $true, else $false.
This example checks whether the input was a number or a dot:
$text = '12.98' $hasOtherCharacters = $text -cmatch '[^0-9.]' "$text has illegal characters? $hasOtherCharacters"
The result would be:
12.98 has illegal characters? False
If the text contained a comma instead of a dot, the result would be different because the comma is considered illegal:
$text = '12,98' $hasOtherCharacters = $text -cmatch '[^0-9.]' "$text has illegal characters? $hasOtherCharacters"
12,98 has illegal characters? True
