It’s hard to know exactly where your error is without seeing the rest of the code or the error logs. In general, you seem to going in the right direction. Here’s a working example:

<?php
$user_data = <<<EOD
#!/bin/bash
apt-get -y update
apt-get -y install nginx
export HOSTNAME=$(curl -s http://169.254.169.254/metadata/v1/hostname)
export PUBLIC_IPV4=$(curl -s http://169.254.169.254/metadata/v1/interfaces/public/0/ipv4/address)
echo Droplet: \$HOSTNAME, IP Address: \$PUBLIC_IPV4 > /usr/share/nginx/html/index.html
EOD;

$data = array(
    'name'               => 'nginx-droplet',
    'region'             => 'nyc3',
    'size'               => '512mb',
    'image'              => 'ubuntu-14-04-x64',
    'user_data'          => $user_data
);

$data_string = json_encode($data);

$ch = curl_init('https://api.digitalocean.com/v2/droplets');
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
curl_setopt($ch, CURLOPT_POSTFIELDS, $data_string);
curl_setopt($ch, CURLOPT_HTTPHEADER, array(
    'Authorization: Bearer YOUR_TOKEN_API_HERE',
    'Content-Type: application/json',
    'Content-Length: ' . strlen($data_string))
);

$result = curl_exec($ch);
print_r($result);
?>

Note that the $HOSTNAME is escaped like \$HOSTNAME in order to prevent PHP from attempting to treat it as a variable.

For more information on the DigitalOcean metadata service see: An Introduction to Droplet Metadata

You might also want to check out the community contributed PHP bindings for DgitialOcean’s APIv2.

Thanks .
I got an error with this coding though as i dint get the hostname and ip to show on the html file
this was the coding used in v 1 api now i am using v2
export HOSTNAME=$(curl -s http://169.254.169.254/metadata/v1/hostname)
export PUBLICIPV4=$(curl -s http://169.254.169.254/metadata/v1/interfaces/public/0/ipv4/address)
echo Droplet: \$HOSTNAME, IP Address: \$PUBLICIPV4 > /usr/share/nginx/html/index.html

as i am using v2 api now ,How can i get the hostname with the new API . The new api is not easy to understand for me as i am beginner in coding.
Any help would be appreciated
Thanks.