I want to `grep` only group IDs from `/etc/passwd`. Now I only came up how to grep the names, with:

```
grep -oE '^[^:]+' /etc/passwd

```

which gives me:

```
[frynio@manjaro ~]$ grep -oE '^[^:]+' /etc/passwd
root
nobody
dbus
bin
daemon
mail
ftp
http
systemd-journal-remote
systemd-coredump
uuidd
dnsmasq
rpc
usbmux
avahi
colord
cups
deluge
git
lightdm
nm-openconnect
nm-openvpn
ntp
polkitd
frynio

```

How can I change this regex, to omit the first three `:`s and then start matching with `[^:]+`? (cuz the `^` before it matches the beginning of the line, that's why I can extract the names, and I want something to match the position after 3 colons).

PS I **have** to use `grep`