Regular expressions and [ ]

 Regular expressions and [ ] 

[ ] is space for characters which you need. 

for example: 

1) we have user Ostrozub

2) grep this: 

grep -i ostrozub /etc/passwd

3) What ist the name? Ostrizub? Ostrozub? Ostrrzub? Ostrpzub?

- check this via [ ] - [i-r] ?

[i-r] matches from i to r? ... i, j, k, l, m, n, o, p, r

check this picture:

Ostrozub (o) is not matches from a to g.