Regex plus - match the previous element 1 or more times

0+

will match strings:

0
00
000

and so on

0+ cannot be used in grep because the grep by default uses basic regular expressions that means: to use the + operator we should add a \ in front of it so it will become \+. So our command becomes this:

grep -r '0\+' /etc

To use 0+ - use extended grep:

egrep -r '0+' /etc