cURL is a powerful library and command-line tool which allows the transfer of data using different protocols, such as FTP, HTTP, HTTPS, IMAP etc etc. For a full list and more information please visit https://curl.haxx.se/.

In the demonstrations below I'll be using the curl library for PHP. To find out if the cURL extension is enabled in your PHP environment, you can simply run the phpinfo() function and search for cURL, if enabled you should see something like the below;


curl

cURL support => enabled
cURL Information => 7.59.0
Age => 4
Features
AsynchDNS => Yes
CharConv => No
Debug => No
GSS-Negotiate => No
IDN => Yes
IPv6 => Yes
krb4 => No
Largefile => Yes
libz => Yes
NTLM => Yes
NTLMWB => No
SPNEGO => Yes
SSL => Yes
SSPI => Yes
TLS-SRP => No
HTTP2 => Yes
GSSAPI => No
KERBEROS5 => Yes
UNIX_SOCKETS => No
PSL => No
Protocols => dict, file, ftp, ftps, gopher, http, https, imap, imaps, ldap, pop3, pop3s, rtsp, scp, sftp, smb, smbs, smtp, smtps, telnet, tftp
Host => x86_64-pc-win32
SSL Version => OpenSSL/1.1.0h
ZLib Version => 1.2.11
libSSH Version => libssh2/1.8.0

This also gives a quick readout of the protocols supported!

You can also use the PHP function function_exists() to see if you can initialize cURL.


echo (function_exists("curl_init") ? "cURL Function Exists" : "cURL Function Doesn't Exist");

If one of these methods shows that the cURL library doesn't exist you will need to talk to your host or enable the curl extension yourself in your php.ini file.

Checking the http status code of a remote resource with cURL

In the below I'll show you to get an array of information regarding the cURL transfer, using this we can then see the outcome of the request and the http_code. I've also set an option to let curl know that it should exclude the body from the output.


$ch = curl_init("http://url/to/remote/resource");
curl_setopt_array($ch, array(
    CURLOPT_NOBODY => true,
    )
);
curl_exec($ch);
print_r(curl_getinfo($ch));
curl_close($ch);

// Output 
Array
(
    [url] => http://url/to/remote/resource
    [content_type] => text/html; charset=UTF-8
    [http_code] => 200
    [header_size] => 199
    [request_size] => 59
    [filetime] => -1
    [ssl_verify_result] => 20
    [redirect_count] => 0
    [total_time] => 0.421
    [namelookup_time] => 0.015
    [connect_time] => 0.109
    [pretransfer_time] => 0.343
    [size_upload] => 0
    [size_download] => 0
    [speed_download] => 0
    [speed_upload] => 0
    [download_content_length] => -1
    [upload_content_length] => -1
    [starttransfer_time] => 0.421
    [redirect_time] => 0
    [redirect_url] => 
    [primary_ip] => x.x.x.x
    [certinfo] => Array
        (
        )

    [primary_port] => 443
    [local_ip] => x.x.x.x
    [local_port] => 49600
)

If you're wanting a specific detail from the array, you can set a CURLINFO option like the below which will only return that specific piece of data, the http_code in this example.


print_r(curl_getinfo($ch, CURLINFO_HTTP_CODE));

I strongly suggest you look over the PHP manual to do with cURL, curl_setopt and curl_getinfo to see what else can be done.