curl
#curl
Table of Contents
About 1
Chapter 1: Getting started with curl 2
Remarks 2
Examples 2
Transfer data using curl 2
Using curl in PHP to fetch data 2
Using curl through the command line 2
Use the libcurl easy C API to get a remote resource 3
Chapter 2: Curl Installation 4
Examples 4
From packages 4
Chapter 3: Name resolve curl tricks 5
Examples 5
Editing the hosts file 5
Providing custom IP address for a name 5
Change the "Host:" header 5
Credits 7
About
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https://riptutorial.com/ 1
Chapter 1: Getting started with curl
Remarks
This section provides an overview of what curl is, and why a developer might want to use it.
It should also mention any large subjects within curl, and link out to the related topics. Since the
Documentation for curl is new, you may need to create initial versions of those related topics.
Examples
Transfer data using curl
cURL is the name of the project which depicts: 'Client for URLs' and also be called as Client URL
Request Library
it combines two separate packages: curl and libcurl.
1. curl is a command line tool used to get documents/files from or send documents to a server,
using any of the supported protocols: DICT, FILE, FTP, FTPS, Gopher, HTTP, HTTPS,
IMAP, IMAPS, LDAP, LDAPS, POP3, POP3S, RTMP, RTSP, SCP, SFTP, SMB, SMTP,
SMTPS, Telnet and TFTP.
2. libcurl is the underlying library curl uses to do the actual networking and transfer work.
libcurl is used by thousands of services, applications and devices and very often through one
of the "language bindings" that allows programmers of higher level languages to access its
powers.
Using curl in PHP to fetch data
<?php
$ch = curl_init(); //curl handler init
curl_setopt($ch,CURLOPT_URL,"http://www.google.com/search?q=curl");
curl_setopt($ch,CURLOPT_RETURNTRANSFER,true);// set optional params
curl_setopt($ch,CURLOPT_HEADER, false);
$result=curl_exec($ch);
curl_close($ch);
echo $result;
?>
Using curl through the command line
Show curl version:
https://riptutorial.com/ 2
curl --version
GET a remote resource and have it displayed in the terminal:
curl http://stackoverflow.com
GET a remote resource and save it in a local file:
curl -o file https://stackoverflow.com
Add headers to response:
curl -i http://stackoverflow.com
Output only headers:
curl -I http://stackoverflow.com
Use the libcurl easy C API to get a remote resource
#include <stdio.h>
#include <curl/curl.h>
int main(void)
{
CURL *curl;
CURLcode res;
curl = curl_easy_init();
if(curl) {
curl_easy_setopt(curl, CURLOPT_URL, "http://example.com");
/* example.com is redirected, so we tell libcurl to follow redirection */
curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1L);
/* Perform the request, res will get the return code */
res = curl_easy_perform(curl);
/* Check for errors */
if(res != CURLE_OK)
fprintf(stderr, "curl_easy_perform() failed: %s\n",
curl_easy_strerror(res));
/* always cleanup */
curl_easy_cleanup(curl);
}
return 0;
}
Read Getting started with curl online: https://riptutorial.com/curl/topic/4246/getting-started-with-curl
https://riptutorial.com/ 3
Chapter 2: Curl Installation
Examples
From packages
The curl source packages can be downloaded from the following page:
https://curl.haxx.se/download.html
However, the best way to install it is to use your package repository.
For Linux distros, you can use apt-get, yum or rpm depending on the distribution you are using, so
the exact command will be:
apt-get install curl
Or:
yum install curl
For Mac users, you can install curl via Homebrew. More details here:
http://brewformulas.org/Curl
Read Curl Installation online: https://riptutorial.com/curl/topic/10591/curl-installation
https://riptutorial.com/ 4
Chapter 3: Name resolve curl tricks
Examples
Editing the hosts file
The easiest way to connect via curl to a different server is to alter the hosts file on your machine.
On Linux and Unix systems, the hosts file is located in /etc/hosts, while on Windows systems it
will be located in c:\windows\system32\drivers\etc\hosts.
Once you open the file with a text editor of your choice, add
1.2.3.4 domain.tld www.domain.tld
This is basically the IP of the server you would like to resolve the domain to followed by the
domain and a www version of the domain.
Curl will then resolve to this domain until the added line in the hosts file is removed.
The limitation in this example is that editing the hosts file often requires admin access and also, it
affects all applications connected to the domain at the same time.
Providing custom IP address for a name
The most effective way to resolve curl to a different server is to use the --resolve option. This
option will insert the address into curl's DNS cache, so it will effectively make curl believe that's the
address it got when it resolved the name. Like so:
curl --resolve eaxmple.com:80:1.2.3.4 http://example.com/
In the above example, firstly we specify the domain (example.com), then we ask it to connect on
port 80 to the IP 1.2.3.4. Depending on the protocol used and the server's configuration, the port
can vary. For HTTP the port is 80 and for HTTPS, the port is 443.
It is important to note here that the --resolve option will send SNI for the name in the URL. This
means that when connecting to the server via HTTPS, curl will verify the server's response to
make sure it servers for the name in the URL. In other words, it will ensure there is an SSL on the
server installed for the domain.
Change the "Host:" header
The "Host:" header is a normal way an HTTP client tells the HTTP server which server it speaks
to. By passing custom modified "Host:" header you can have the server respond with the content
of the site, even if you didn't actually connect to the host name.
For example, if you have a site on your localhost and you wish to have curl ask for its index page,
the command is:
https://riptutorial.com/ 5
curl -H "Host: example.com" http://localhost/
The main disadvantage of modifying the "Host:" header is that curl will only extract the SNI name
to send from the given URL. In other words, the "Host:" header modification is not enough when
communication with a server via HTTPS.
Read Name resolve curl tricks online: https://riptutorial.com/curl/topic/10565/name-resolve-curl-
tricks
https://riptutorial.com/ 6
Credits
S.
Chapters Contributors
No
Getting started with Alexander Prokofyev, Altaf Hussain, Community, Daniel
1
curl Stenberg, Danilo Terra, Riad
2 Curl Installation Zdravko B
Name resolve curl
3 Zdravko B
tricks
https://riptutorial.com/ 7
