grep, and which regular expression

grep prints the lines that match, and its exit status is the answer when you do not want the lines: 0 matched, 1 did not, 2 something went wrong.

The pattern is a regular expression, not a glob. . matches any character and * means 'zero or more of the previous thing' — the opposite of what a glob's * means.

In a basic regular expression — the default — +, ?, |, ( and ) are ordinary characters, and their escaped forms are the operators. In an extended one, reached with -E, it is the other way round.

This is backwards from every other regular-expression dialect, which is why grep -E is usually the one you want.