Use grep to match a pattern in a line only once

I have this:

 echo 12345 | grep -o '[[:digit:]]{1,4}'

Which gives this:

1234
5

I understand whats happening. How do I stop grep from trying to continue matching after 1 successful match?

How do I get only

1234

Answer

You need to do the grouping: (...) followed by the exact number of occurrence: {<n>} to do the job:

maci:~ san$ echo 12345 | grep -o '([[:digit:]]){4}'
1234

Hope it helps. Cheers!!