extract username from email address

I'm trying to get the username portion of an email
address.  No match though.  Any tips?

"From: Somebody <username(_at_)somedomain(_dot_)com>"

:0
* ^From:\/.*
{
  FROM = "$MATCH"
}

:0
* FROM ?? (?<=<)[^(_at_)]*
{
  USERNAME = "$MATCH"
}

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