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Found this useful for scripts where I needed to work with the machine's IP. If $DEVICE is not specified, this will return all IPs on the machine. If $DEVICE is set to a network adapter, it will return just that adapter's IP.
Next time you are leaching off of someone else's wifi use this command before you start your bittorrent ...for legitimate files only of course.
It creates a hexidecimal string using md5sum from the first few lines of /dev/urandom and splices it into the proper MAC address format. Then it changes your MAC and resets your wireless (wlan0:0).
get desired info from machine and pipe it txt file.
The command above has been changed due to very good constructive criticism - thanks x 2! This command can be used after acquiring mac's, ip's and hostname's or any of the above from a freshly scanned LAN. User must be root, and remember to change your settings on your network managing software manually (Fedc10 NetworkManager Applet 0.7.1 is mine) instead of 'auto DHCP'. You can also substitute eth0 for wlan0 etc - be good and ENJOY!
eth0 = the name of the interface
00:01:02:03:04:05 = the new mac adresse
the same thing for wireless card $ sudo iwconfig eth1 hw ether 00:01:02:03:04:05
This is useful if you have need to do port forwarding and your router doesn't assign static IPs, you can add it to a script in a cron job that checks if you IP as recently changed or with a trigger script.
This was tested on Mac OSX.
You can use this to loop any command to periodically see the output.
while true; do [YOUR COMMAND HERE]; sleep [# of seconds]; done;
Alternatively, you can put it in a simple shell script to save typing!
while true; do $1; sleep $2; done;
/path/to/script.sh "ifconfig eth0 | grep 'inet addr:'" 60
Needed to get the Mac of various devices on a solaris box, but didn't have root. This command used awk to display the Network device, the IP, and the MAC a line at a time.
On the Mac, the format ifconfig puts out is little different from Linux: the IP address is space separated, instead of colon. That makes parsing the IP address easier. See releated command for Linux/Unix: