How to make grep stop at first match on a line?

Question

Well, I have a file test.txt

#test.txt
odsdsdoddf112 test1_for_grep
dad23392eeedJ test2 for grep
Hello World test
garbage

I want to extract strings which h

Answer 1

If you're sure you have no leading whitespace, add a ^ to match only at the start of a line, and change the * to a + to match only when you have one or more alphanumeric characters. (That means adding -E to use extended regular expressions).

grep -Eo "^[[:alnum:]]+[[:blank:]]" test.txt

(I also removed the . from the middle; I'm not sure what that was doing there?)