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

Just awk, no need combination of tools.

# awk '{for(i=1;i<=NF;i++){if($i~/^th/){print $i}}}' file
the
the
the
this
thoroughly

Answer 2

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

---

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

Answer 3

To search all the words with start with "icon-" the following command works perfect. I am using Ack here which is similar to grep but with better options and nice formatting.

ack -oh --type=html "\w*icon-\w*" | sort | uniq

Answer 4

You could translate spaces to newlines and then grep, e.g.:

cat * | tr ' ' '\n' | grep th

Answer 5

Try grep -o

grep -oh "\w*th\w*" *

Edit: matching from Phil's comment

From the docs:

-h, --no-filename
    Suppress the prefixing of file names on output. This is the default
    when there is only  one  file  (or only standard input) to search.
-o, --only-matching
    Print  only  the matched (non-empty) parts of a matching line,
    with each such part on a separate output line.

Answer 6

$ grep -w

Excerpt from grep man page:

-w: Select only those lines containing matches that form whole words. The test is that the matching substring must either be at the beginning of the line, or preceded by a non-word constituent character.