ack regex: Matching two words in order in the same line

I would like to find lines in files that include two words, word_1 and word_2 in order, such as in Line A below, but not as in Line B or Line C:

Line A: ... word_1 .... word_2 .... 
Line B: ... word_1 ....
Line C: ... word_2 ....

I have tried

$ack '*word_1*word_2'
$ack '(word_1)+*(word_2)+'

and the same commands with ^ appended at the beginning of the regex (in an attempt to follow the Perl regex syntax).

None of these commands return the fil开发者_StackOverflow中文版es or the lines I am interested in.

What am I doing wrong?

Thanks!

You want to find word_1, followed by anything, any number of times, followed by word_2. That should be

word_1.*word_2

You seem to be using * as it is often used in command line searches, but in regexes is it a quantifier for the preceding character, meaning match it at least 0 times. For example, the regex a* would match 0 or more as, whereas the regex a+ would match at least one a.

The regex metacharacter meaning "match anything" is ., so .* means "match anything, any number of times. See perlrequick for a brief introduction on the topic.