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.