Write example

Many times you need special priviliges to open files or perform other actions  that are not available to your existing uid/gid.

         $ ls -la /dev/tty1
         crw--w----  1 bree   tty        4,   1 Apr 18 14:00 /dev/tty1

         $ id
         uid=1010(bri) gid=1010(bri) groups=1010(bri)
         
         $ ls -la /usr/bin/write
         -rwxr-sr-x  1 root   tty          7540 Jul  4  2002 write

/usr/bin/write is run with group 'tty' because of the 's' bit in the group field.