shell - Strange regex behavior with grep -

grep '[:digit:]{1,}-{1,}' *.txt| wc -l 

this command outputs: 0

grep '1-' *.txt| wc -l 

however, command outputs: 10598

both commands being run same directory. first command should have returned greater or equal output of second command. can shed insight going on here?

echo 1 | grep '[:digit:]' #nothing.... 

grep uses different syntax, need [[:digit:]] or [0-9].

the {1,} syntax not supported basic grep, can use other modes, extended 1 -e... note: 1 use + matching 1 or more characters....

general note: test regexes in small parts see each part thought does. once expression gets complicated, it's hard tell went wrong.