How do I find my server's IP address in PHP(CLI)

You can get the hostname by using gethostname

try this it should return the ip address of the server

$host= gethostname();
$ip = gethostbyname($host);

If you are working with PHP < 5.3, this may help (on *NIX based systems atleast):

 mscharley@S04:~$ cat test.php
#!/usr/bin/env php
<?php

function getIPs($withV6 = true) {
    preg_match_all('/inet'.($withV6 ? '6?' : '').' addr: ?([^ ]+)/', `ifconfig`, $ips);
    return $ips[1];
}

$ips = getIPs();
var_dump($ips);

 mscharley@S04:~$ ./test.php
array(5) {
  [0]=>
  string(13) "72.67.113.141"
  [1]=>
  string(27) "fe80::21c:c0ff:fe4a:d09d/64"
  [2]=>
  string(13) "72.67.113.140"
  [3]=>
  string(9) "127.0.0.1"
  [4]=>
  string(7) "::1/128"
}
 mscharley@S04:~$

Or, if you don't anticipate doing it often, then perhaps this would work (just don't abuse it):

$ip = file_get_contents('http://whatismyip.org/');