カテゴリ:

All users are listed in a file /etc/passwd.

$ cat /etc/passwd
root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:/sbin/nologin
daemon:x:2:2:daemon:/sbin:/sbin/nologin

With a command awk, you could get the first field easily.

$ awk -F':' '{ print $1 }' /etc/passwd | sort
adm
apache
bin