Grep : what is the difference between options -o and -c?

Linux
1

I would like see practical examples of the differences between -o and -c with grep command

echo a.b.c.d | grep -o “[.]” | wc -l

why does it give me output 3 and not 4 ? i have four dots

2

The -o option shows only matched part in your regex/word. For example, in the following, if you want to grep xyz word only, then you can do the following:

printf "abc xyz\nxyzzzz\nxyabc\nxyzabc\n" | grep -w -o 'xyz'
# this will grep all other lines matching xyz 
printf "abc xyz\nxyzzzz\nxyabc\nxyzabc\n" | grep 'xyz'

The -c option count matched string/regex etc. Do you want to count ‘xyz’ word in the string? Try

printf "abc xyz\nxyzzzz\nxyabc\nxyzabc\n" | grep -w -o  -c 'xyz'
# this will grep all other lines matching xyz 
printf "abc xyz\nxyzzzz\nxyabc\nxyzabc\n" | grep  -c 'xyz'

I hope this helps.

3

I see that you attach option -w with -o , is it necessary ?

4

That is to make examples clear. It all depends upon what kind of output you want and what input is provided. I hope this helps.