That's because '\d' is rexeg-speak for a digit: '0' to '9', Since your string contains "abcdefgh" and no digits at all, it will never match.
Try
@"DATE=.{7}"
for seven of any character, or:
@"DATE=\w{7}"
for seven alphnumerics, or:
@"DATE=[a-zA-Z]{7}"
for seven upper or lower case alphabetics.
Get a copy of
Expresso [
^] - it's free, and it examines and generates Regular expressions.