Can grep show only words that match search pattern?

Question

Is there a way to make grep output \"words\" from files that match the search expression?

If I want to find all the instances of, say, \"th\" in a number of files, I

Answer 1

I was unsatisfied with awk's hard to remember syntax but I liked the idea of using one utility to do this.

It seems like ack (or ack-grep if you use Ubuntu) can do this easily:

# ack-grep -ho "\bth.*?\b" *

the
the
the
this
thoroughly

If you omit the -h flag you get:

# ack-grep -o "\bth.*?\b" *

some-other-text-file
1:the

some-text-file
1:the
the

yet-another-text-file
1:this
thoroughly

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As a bonus, you can use the --output flag to do this for more complex searches with just about the easiest syntax I've found:

# echo "bug: 1, id: 5, time: 12/27/2010" > test-file
# ack-grep -ho "bug: (\d*), id: (\d*), time: (.*)" --output '$1, $2, $3' test-file

1, 5, 12/27/2010