[SOLVED] Regex to match string NOT containing specific character or more than one character

Regex to match string NOT containing specific character or more than one character

Trying to get .NET regex to recognize the following string (A), but not string (B). Specific requirements to use .NET flavor of regex.

(A) :: John Doe <JDoe@domain.com>
(B) :: John Doe <JDoe@domain.com>, Jane Dina <JDina@domain.com>

Have tried quite a few options here including the following, but haven't gotten it to work the way I need it to (for more context, this is going to be used in an Exchange Online Transport Rule to filter messages that have ONLY one recipient, no more than one.

^[^<]+<[^>]+>$ - fails, recognizes both
^.*(?=[^,])$ - fails, recognizes none
^[^,]$ - fails, recognizes both

Let me know if there are additional details I can provide.

Dustin

Solution

The following regex - the first one you mention as failing - does work, with individual single-line strings as input:

^[^<]+<[^>]+>$

With multiline input, you need the Multiline regex option, which can be specified inline via (?m), so that ^ and $ match on each line:

(?m)^[^<]+<[^>]+>$

For an explanation of the regex and the option to experiment with it, see this regex101.com page.

Using PowerShell to demonstrate the solution:

With individual strings as input:

# Matches and outputs only the (A) input string.
@(
  '(A) :: John Doe <JDoe@domain.com>',
  '(B) :: John Doe <JDoe@domain.com>, Jane Dina <JDina@domain.com>'
) -match '^[^<]+<[^>]+>$'

With a multiline string as input:

[regex]::Matches(
  @'
(A) :: John Doe <JDoe@domain.com>
(B) :: John Doe <JDoe@domain.com>, Jane Dina <JDina@domain.com>
'@,
  '(?m)^[^,]+<[^>]+>$'
).Value