Count number of occurrences of a pattern in a file (even on same line)

Question

When searching for number of occurrences of a string in a file, I generally use:

grep pattern file | wc -l

However, this only finds one occurrence per line, because of the way grep works. How can I search for the number of times a string appears in a file, regardless of whether they are on the same or different lines?

Also, what if I'm searching for a regex pattern, not a simple string? How can I count those, or, even better, print each match on a new line?

Answer 1

To count all occurrences, use -o. Try this:

echo afoobarfoobar | grep -o foo | wc -l

And man grep of course (:

Update

Some suggest to use just grep -co foo instead of grep -o foo | wc -l.

Don't.

This shortcut won't work in all cases. Man page says:

-c print a count of matching lines

Difference in these approaches is illustrated below:

1.

$ echo afoobarfoobar | grep -oc foo
1

As soon as the match is found in the line (a{foo}barfoobar) the searching stops. Only one line was checked and it matched, so the output is 1. Actually -o is ignored here and you could just use grep -c instead.

2.

$ echo afoobarfoobar | grep -o foo
foo
foo

$ echo afoobarfoobar | grep -o foo | wc -l
2

Two matches are found in the line (a{foo}bar{foo}bar) because we explicitly asked to find every occurrence (-o). Every occurence is printed on a separate line, and wc -l just counts the number of lines in the output.