Many actions on the internet are something we’re used to doing through a browser: reading websites, downloading files, filling out forms, or submitting data. But did you know that all of this can be done faster directly from the command line? One of the best tools for this is cURL.
cURL offers more control and convenience when you need to handle multiple requests or data. And when you use cURL with a proxy, the possibilities expand even further: you can bypass restrictions and remain anonymous.
In this article, we’ll explain how cURL helps download files, send requests, and work with proxies to bypass blocks and protect your anonymity. We’ll also look at how to use cURL for web scraping and avoid common errors. Simple examples and useful tips — all of that awaits you below!
So, cURL (Client URL) is a utility based on the libcurl library that allows you to send and receive data over the internet. It operates directly from the command line and supports various protocols (HTTP, HTTPS for interacting with web pages, FTP for file handling, and many others).
With cURL, you can do various things, such as:
- Download files from the internet.
- Send data to a server.
- Work with websites or APIs.
- Use proxy servers for anonymity or bypassing blocks.
cURL helps automate routine tasks, and it does so quickly and conveniently, especially when you need to make many requests or operations. cURL is often used for testing, web scraping, and working with services and applications that require data transmission over the internet. It is a powerful tool for developers and system administrators, as well as for any users who need to interact with online resources from the command line or scripts.
A proxy (or proxy server) is an intermediary between your device and the internet. When you want to visit a website, your request first goes to the proxy, which then forwards it to the appropriate server and returns the response to you. This allows you to interact with the internet in a slightly different way.
Here are a few reasons to use proxy servers:
Hiding Your IP Address
A proxy can hide your real IP address, so websites will see the proxy server's IP instead of yours. This helps increase your anonymity on the internet.
Bypassing Restrictions
Sometimes, internet resources limit access based on regions. With a proxy, you can bypass these restrictions and access content that is normally unavailable in your country.
Improving Speed
Some proxy servers can cache data, which helps speed up the loading of websites you visit frequently.
Content Filtering
Proxies can be configured to block unwanted websites or protect you from viruses and other threats.
Additional Security
A proxy helps protect you from malicious websites and phishing attacks, providing an extra layer of security.
There are different types of proxies—HTTP, HTTPS, SOCKS, and others. Each type of proxy has its own features and uses depending on your needs. HTTP is used for standard web requests, HTTPS for secure, encrypted connections, and SOCKS is a universal proxy that can handle any type of traffic, including HTTP and HTTPS. Let’s take a closer look at them in the next section.
Choosing a proxy depends on your goals, tasks, and requirements for performance or anonymity. Let’s look at the main types of proxies and what they are best used for:
HTTP/HTTPS Proxies
HTTP proxies work only with HTTP/HTTPS protocols and provide additional encryption, making them more secure.
They are widely supported by most tools and software. These are great for web scraping and other tasks that require automation.
SOCKS Proxies (SOCKS4 and SOCKS5)
SOCKS5 supports both TCP and UDP traffic.
It operates at a lower level than HTTP proxies, making it versatile for any protocol.
SOCKS proxies do not handle headers, which increases anonymity.
For tasks requiring high anonymity or working with non-standard protocols, SOCKS5 is the best option.
Free Proxies
Free proxies are typically slow, unstable, and quickly blocked.
They can expose your data to risks, as they don’t always provide security.
A common choice for testing or learning, but not recommended for large projects.
Data Center Proxies
These use IP addresses belonging to data centers rather than Internet Service Providers (ISPs).
They are faster and cheaper than residential proxies but are more easily detected by websites since their IP addresses are often grouped and share similar characteristics.
Residential Proxies
These use real IP addresses provided by ISPs.
They are harder for websites to detect compared to data center proxies.
For working with websites that block standard proxies, residential proxies help you appear as a regular user.
Mobile Proxies
IP addresses are linked to mobile carriers.
They are very hard to block or detect. Typically, they are more expensive than other proxy types.
If you're working with websites that require mobile traffic or have advanced anti-bot systems, mobile proxies are indispensable.
Proxy rotation helps avoid blocks and enhances anonymity. It allows you to dynamically change the IP addresses from which requests are sent, reducing the risk of being blocked for making frequent requests from a single IP.
How to set up proxy rotation with cURL:
- Using an API to obtain proxies: Many specialized services (such as ProxyMesh) offer APIs to get proxy servers. In this example, you'll need to replace your_username and your_password with your actual login and password provided by the ProxyMesh service:
PROXY=$(curl -s 'https://proxy.proxyMesh.com/api/proxy?username=your_username&password=your_password')
curl -x $PROXY http://example.com/ip
- Suppose you have a list of proxies, for example, from public or paid services. Here's an example with multiple proxy servers:
proxies=("http://123.45.67.89:8080" "http://98.76.54.32:8080" "http://165.178.0.1:8080")
PROXY=${proxies[$RANDOM % ${#proxies[@]}]}
curl -x $PROXY http://example.com/ip
If you’re using cURL as part of a more complex project, you can use third-party tools or libraries for proxy rotation on Unix systems, such as proxychains. Install proxychains and configure the settings in /etc/proxychains.conf to enable automatic proxy rotation.
proxychains curl http://example.com
cURL supports a wide range of protocols, allowing you to work with different types of network connections. Depending on your tasks, you can choose the appropriate protocol and work with it using simple commands in the command line. Here’s an overview of the main protocols you can use with cURL:
HTTP (HyperText Transfer Protocol)
One of the most popular protocols for data transfer on the internet. It is used for exchanging data between a client (e.g., a browser) and a server.
Example usage: curl http://example.com
Default port: 80
HTTPS (HyperText Transfer Protocol Secure)
A secure version of HTTP, using SSL/TLS for data encryption and protection against "man-in-the-middle" attacks.
Example usage: curl https://example.com
Default port: 443
SOCKS (Socket Secure)
A proxy protocol that allows the transmission of any type of data over the internet, including HTTP, FTP, and other protocols, operating at the socket level.
Example usage: curl --proxy socks5://proxy_host:proxy_port http://example.com
Default port: 1080
FTP (File Transfer Protocol)
A protocol for transferring files between a client and a server. It does not encrypt transmitted data.
Example usage: curl ftp://example.com/file.txt
Default port: 21
FTPS (FTP Secure)
An extension of FTP, adding encryption with SSL/TLS to secure the transmitted data.
Example usage: curl ftps://example.com/file.txt
Default port: 990 (for FTPS-implicit) or 21 (for FTPS-explicit)
SFTP (SSH File Transfer Protocol)
A protocol for transferring files, using SSH for encryption and ensuring data security.
Example usage: curl sftp://example.com/file.txt
Default port: 22
LDAP (Lightweight Directory Access Protocol)
A protocol for accessing and managing directory services, such as Active Directory or OpenLDAP.
Example usage: curl ldap://example.com
Default port: 389
POP3 (Post Office Protocol)
A protocol for receiving email from a mail server.
Example usage: curl pop3://pop.example.com
Default port: 110
IMAP (Internet Message Access Protocol)
A protocol for accessing and managing email on a server.
Example usage: curl imap://imap.example.com
Default port: 143
In Windows, macOS, and Linux, cURL is already pre-installed. You can check this by running the following command in the terminal (for Windows, use cmd or PowerShell):
curl --version
The response should display information about the cURL and libcurl versions, along with the supported protocols and features. If an error message appears instead, such as:
Linux/macOS: command not found
Windows: 'curl' is not recognized as an internal or external command
This means cURL is either not installed or not added to the environment variables. In that case, you need to install cURL manually for your operating system:
Windows
- Download the ready-to-use archive with curl.exe from the official website.
- Extract the archive and add the path to curl.exe to the PATH environment variables.
Or you can use winget to install cURL:
winget install curl
macOS
To update or install, use Homebrew:
brew install curl
Linux
Ubuntu/Debian:
sudo apt update
sudo apt install curl
Fedora/RHEL/CentOS:
sudo dnf install curl # Fedora
sudo yum install curl # CentOS/RHEL
Arch Linux:
sudo pacman -S curl
Let’s look at the commands that cover the main use cases of cURL — downloading data, making requests, and managing files:
- Fetching page content (GET request):
curl http://example.com
This command is used to fetch the content of a webpage. cURL makes a request to the specified URL and displays the result on the screen (usually the HTML code of the page). This is useful for retrieving information from websites, scanning content, or testing the availability of web resources.
- POST request (used for sending data to a server, such as when submitting forms):
curl -X POST -d "param1=value1¶m2=value2" https://example.com
-X POST specifies the POST request method.
-d allows you to specify the data being sent to the server.
Example with a real website:
curl -X POST -d "name=JohnDoe&email=johndoe@example.com" https://httpbin.org/post
Additional parameters for the POST request:
Using headers with -H:
curl -X POST -d "param1=value1" -H "Content-Type: application/x-www-form-urlencoded" https://example.com
Sending JSON data:
curl -X POST -H "Content-Type: application/json" -d '{"key":"value"}' https://example.com
- Downloading a file from a URL (using the test site https://www.sample-videos.com):
To download and save a file in the current working directory, simply use the command with the -O (uppercase letter) option, which saves the file with the name specified in the URL.
curl https://www.sample-videos.com/img/Sample-jpg-image-50kb.jpg -O
If you need to download a file to a specific folder, additionally specify the path using the -o (lowercase letter) option:
Windows:
curl -o "C:\Users\UserName\Pictures\Sample-jpg-image-50kb.jpg" https://www.sample-videos.com/img/Sample-jpg-image-50kb.jpg
Linux/MacOS:
curl -o "/Users/UserName/Pictures/Sample-jpg-image-50kb.jpg" https://www.sample-videos.com/img/Sample-jpg-image-50kb.jpg
- Checking the response headers:
curl -I http://example.com
The command displays only the response headers from the server, without the body of the response. The -I (or --head) flag allows you to see the meta information about the page (such as the HTTP status code, content type, date, and time of the last update). This is useful for diagnostics or checking the availability of a resource.
- To authenticate using a username and password on a real website with cURL, you can use the following command:
curl -u username:password https://example.com
Example with a real website:
curl -u demo:password123 https://httpbin.org/basic-auth/demo/password123
- The --header command (or the short form -H) in cURL is used to add HTTP headers to HTTP requests. It allows you to send additional HTTP headers that may be required by the server. For example, you can add a User-Agent:
curl --header "User-Agent: Mozilla/5.0" https://example.com
Or configure authentication using headers:
curl --header "Authorization: Bearer your_token_here" https://api.example.com
To view all available commands and their descriptions, use the command:
curl --help all
Invoke-WebRequest is a PowerShell cmdlet used for making HTTP requests, such as downloading web pages, sending data, or downloading files. It allows you to interact with web content directly from the command line, but it is not a full replacement for cURL, as it has more limited functionality and syntax.
Earlier, in PowerShell, the curl command was an alias for Invoke-WebRequest, which often confused users who expected the standard cURL utility to work.
In later versions (Windows 10 and Windows 11), Microsoft added curl.exe — a full version of cURL, similar to what is available on Linux and macOS. However, in PowerShell, the curl command may still trigger Invoke-WebRequest. To avoid this, you can use cmd instead of PowerShell, or remove the curl alias with the command Remove-Alias curl, so that curl directly calls the cURL utility. Alternatively, you can explicitly specify curl.exe:
curl.exe https://example.com
Working with proxy servers in cURL provides you with anonymity, the ability to bypass blocks, and increased security when interacting with online resources. Knowing the basic commands and parameters allows you to effectively set up proxy usage in various scenarios.
Using HTTP and HTTPS proxies
To use an HTTP/HTTPS proxy, you can specify the proxy server with the -x or --proxy parameter:
HTTP proxy:
curl -x http://123.456.789.012:8080 https://example.com
HTTPS proxy:
curl -x https://123.456.789.012:8080 https://example.com
Using SOCKS proxy
SOCKS proxy (SOCKS4 or SOCKS5) supports not only HTTP and HTTPS, but also other protocols.
Example for SOCKS5 proxy:
curl -x socks5://123.456.789.012:1080 https://httpbin.org/ip
Example for SOCKS4 proxy:
curl -x socks4://123.456.789.012:1080 https://httpbin.org/ip
Proxy authentication
Sometimes proxy servers require authentication. To provide a username and password for the proxy, use the -U or --proxy-user parameter.
curl -x http://123.456.789.012:8080 -U testuser:testpassword https://httpbin.org/ip
Using proxies with different protocols
cURL allows you to work with various types of proxies for different protocols. For example, you can use SOCKS5 for HTTP requests and an HTTPS proxy for encrypted connections.
curl -x socks5://123.456.789.012:1080 -U testuser:testpassword https://httpbin.org/ip
This request will use a SOCKS5 proxy to handle HTTP requests, while the data will be transmitted through a secure HTTPS connection.
Checking IP address through a proxy
To verify that the request is indeed passing through the proxy, you can use httpbin.org to get the current IP:
curl -x http://123.456.789.012:3128 http://httpbin.org/ip
Checking proxy speed
To measure the proxy speed in cURL, you can use the -w (write-out) flag to get the download speed (%{speed_download}). The -o /dev/null flag is used to ignore the output content, and -s makes the command run "silently":
curl -x http://123.456.789.012:3128 -o /dev/null -s -w "Download Speed: %{speed_download} bytes/sec\n" https://httpbin.org/bytes/102400
Using proxy with User-Agent headers
Sometimes, it is necessary to spoof the User-Agent when using a proxy.
curl -x http://123.456.789.012:3128 -A "Mozilla/5.0 (Windows NT 10.0; Win64; x64)" http://httpbin.org/headers
Using proxy only for specific requests
You can specify which requests should go through the proxy. For example, use a proxy only for certain domains. The --noproxy option allows you to specify domains that will bypass the proxy:
curl --proxy http://123.456.789.012:8080 --noproxy example.com http://httpbin.org/ip
To simplify the use of proxies in cURL, you can set environment variables. This allows you to automate proxy connections without needing to specify parameters in the command line every time.
Example of using environment variables with cURL:
- Linux/macOS: On Linux and macOS, proxies are set through the terminal using the export command.
Example of setting an environment variable for an HTTP proxy:
export http_proxy=http://123.456.789.012:8080
For an HTTPS proxy:
export https_proxy=https://123.456.789.012:8080
Windows: In Windows, environment variables can be set through the command prompt:
set http_proxy=http://123.456.789.012:8080
set https_proxy=https://123.456.789.012:8080
After this, you can use cURL, and it will automatically use the specified proxy:
curl https://example.com
To use the value of an environment variable in commands or scripts on Linux/macOS, you can use the $ sign. It allows you to refer to the value of the variable. For example:
curl -x $http_proxy https://example.com
To access the value of an environment variable in Windows, the syntax with percent signs % is used. For example:
curl -x %http_proxy% https://example.com
Proper security settings when working with proxies will help prevent data leakage and enhance the protection of your network connections.
Using the -k or --insecure flag: This option allows you to ignore SSL certificate errors, which is useful if your proxy uses a self-signed certificate:
curl -x https://123.456.789.012:8080 -k https://example.com
Certificate verification: To avoid risks when connecting through an HTTPS proxy, it is important to use the correct certificates. If you have a certificate file, use the --cacert flag:
curl -x https://123.456.789.012:8080 --cacert /path/to/certificate.crt https://example.com
If you have multiple certificates, you can specify a directory with trusted certificates using the --capath option. This is useful if you need to work with multiple certificates:
curl -x https://123.456.789.012:8080 --capath /path/to/certificates/ https://example.com
Aliases in cURL are shortened commands for frequently used parameters, making working with cURL more convenient and faster. Instead of typing long commands every time, you can create aliases for commonly repeated tasks.
Why use aliases?
- Simplify commands: Instead of long parameters, you can use short and convenient ones.
- Reduce errors: There is less chance of making mistakes when typing.
- Save time: One alias, and all parameters are already set.
How to set up aliases
Linux/macOS (Unix-like systems):
In these systems, aliases are directly supported by the shell (e.g., bash, zsh, etc.). You can add aliases to your shell configuration files (e.g., .bashrc, .zshrc, etc.) so they are available in any terminal session.
Example for bash:
- Open or create the ~/.bashrc file (or ~/.zshrc for zsh):
nano ~/.bashrc
- Add aliases, for example:
alias curlproxy="curl -x http://123.456.789.012:8080"
After this, you can use the curlproxy command in any session.
curlproxy https://example.com
Windows:
In Windows, alias usage is not supported in the same way as in Unix-like systems. However, in PowerShell, you can create aliases using the New-Alias cmdlet. It is important to note that New-Alias does not allow you to assign parameters for commands, such as a proxy server. Instead, to create aliases with parameters, you can use PowerShell functions or custom scripts.
In PowerShell:
In PowerShell, you can create a function that will act as an alias.
- Open PowerShell.
- Create a function for the alias:
function curlproxy { curl -x http://123.456.789.012:8080 $args }
If you want this function to be available at all times, add it to the PowerShell profile (for example, in the $PROFILE file).
In Command Prompt (CMD):
In CMD, you can use a batch file (.bat) to create aliases. For example, create a curlproxy.bat file in a directory that is included in the system's PATH environment variable, and write the following in this file:
curl -x http://123.456.789.012:8080 %1
Then, you can use the curlproxy command, passing parameters as arguments.
The .curlrc configuration file is a special file used to store default settings for the cURL utility. This file allows you to automate the process of setting command-line parameters such as proxy servers, user agents, SSL certificates, and other options. It's especially useful if you want to avoid specifying the same options every time you run a cURL command.
To configure a proxy in the .curlrc file, simply specify the relevant parameters. For example:
proxy = "http://123.456.789.012:8080"
This parameter tells cURL to use a proxy server with the specified address and port. You can also configure proxy authentication by providing a username and password:
proxy-user = "username:password"
Once you have configured the .curlrc file, cURL will automatically apply these settings when executing commands, so you won't need to specify them manually in the command line. For example, the command:
curl http://example.com
will use the proxy specified in the .curlrc file without the need to add the -x flag or other parameters.
- Suppose you want to extract data from a specific webpage, such as http://example.com. In this case, you can use the following curl command with a proxy:
curl -x http://123.45.67.89:8080 http://example.com -o example.html
Here:
-x http://123.45.67.89:8080 — proxy server.
http://example.com — target webpage from which you want to retrieve data.
-o example.html — saves the webpage content to a file named example.html.
After running the command, example.html will contain the HTML code of the target page.
- Now, let's extract the headers from the webpage https://example.com using a proxy.
Steps:
- Use the proxy server to send requests.
- Apply grep or sed to extract the data.
curl -x http://123.45.67.89:8080 https://example.com | grep -oP '<h1.*?>.*?</h1>'
In PowerShell, you can use the built-in cmdlet Select-String to perform a similar task. For example:
curl.exe -x http://123.45.67.89:8080 https://example.com | Select-String -Pattern '<h1.*?>.*?</h1>' -AllMatches | ForEach-Object { $_.Matches.Value }
If you have WSL (Windows Subsystem for Linux) installed, you can run the same command as on Linux:
curl -x http://123.45.67.89:8080 https://example.com | grep -oP '<h1.*?>.*?</h1>'
Integration of cURL with Python and Node.js opens up numerous opportunities for automating requests, web scraping, and working with APIs. By using the subprocess or pycurl module in Python, or child_process or node-libcurl in Node.js, you can execute complex commands and extract data within your application. Let's take a look at how to integrate cURL with each of these languages.
In Python
To make cURL requests in Python, we use the subprocess module.
GET request with a proxy:
import subprocess
curl_command = ['curl', '-x', 'http://123.45.67.89:8080', 'https://example.com']
response = subprocess.run(curl_command, capture_output=True, text=True)
print(response.stdout)
Let's do the same with pycurl:
import pycurl
from io import BytesIO
# Initialization of the buffer for capturing the output.
buffer = BytesIO()
# Creating a pycurl object
c = pycurl.Curl()
# Setting the URL
c.setopt(c.URL, 'https://example.com')
# Setting the proxy
c.setopt(c.PROXY, 'http://123.45.67.89:8080')
# Setting the output to the buffer
c.setopt(c.WRITEDATA, buffer)
# Performing the request
c.perform()
# Receiving the response
response = buffer.getvalue().decode('utf-8')
# Outputting the response
print(response)
# Clearing
c.close()
In Node.js
To perform cURL requests in Node.js, we use the child_process module.
GET request with a proxy:
const { exec } = require('child_process');
exec('curl -x http://123.45.67.89:8080 https://example.com', (error, stdout, stderr) => {
if (error) console.error(`exec error: ${error}`);
else console.log(stdout);
});
Let's do the same with node-libcurl:
const { Curl } = require('node-libcurl');
const curl = new Curl();
curl.setOpt('URL', 'https://example.com');
curl.setOpt('PROXY', 'http://123.45.67.89:8080');
// Setting a callback for handling the response
curl.on('end', (statusCode, body, headers) => {
console.log(body);
curl.close();
});
curl.on('error', (error) => {
console.error('Error:', error); // Error handling
});
curl.perform();
Integrating CapMonster Cloud with cURL allows you to automate the CAPTCHA solving process when making HTTP requests. Here's how you can do this using cURL:
- First, register on the CapMonster Cloud service and get your API key.
- Create and send a CAPTCHA solving task (in our case, reCAPTCHA v2) via CapMonster Cloud — refer to the documentation:
MacOS/Linux:
curl -X POST https://api.capmonster.cloud/createTask \
-H "Content-Type: application/json" \
-d '{
"clientKey": "API_KEY",
"task": {
"type": "RecaptchaV2TaskProxyless",
"websiteURL": "https://lessons.zennolab.com/captchas/recaptcha/v2_simple.php?level=high",
"websiteKey": "6Lcg7CMUAAAAANphynKgn9YAgA4tQ2KI_iqRyTwd"
}
}'
Windows (CMD):
curl -X POST https://api.capmonster.cloud/createTask ^
-H "Content-Type: application/json" ^
-d "{\"clientKey\":\"API_KEY\",\"task\":{\"type\":\"RecaptchaV2TaskProxyless\",\"websiteURL\":\"https://lessons.zennolab.com/captchas/recaptcha/v2_simple.php?level=high\",\"websiteKey\":\"6Lcg7CMUAAAAANphynKgn9YAgA4tQ2KI_iqRyTwd\"}}"
- Receiving the task result
After the task is submitted, you will receive a task ID, which you will need to get the response.
MacOS/Linux:
curl -X POST https://api.capmonster.cloud/getTaskResult \
-H "Content-Type: application/json" \
-d '{
"clientKey": "API_KEY",
"taskId": "task_id_received_from_createTask"
}'
Windows (CMD):
curl -X POST https://api.capmonster.cloud/getTaskResult ^
-H "Content-Type: application/json" ^
-d "{\"clientKey\":\"API_KEY\",\"taskId\":\"task_id_received_from_createTask\"}"
- CAPTCHA solution
In response to the getTaskResult request, CapMonster will return the solution to the task, for example, a token for reCAPTCHA, which can be used to submit the form.
MacOS/Linux:
curl -X POST https://lessons.zennolab.com/captchas/recaptcha/v2_simple.php \
-d "g-recaptcha-response=your_captcha_solution" \
-d "other_data=value"
Windows (CMD):
curl -X POST https://lessons.zennolab.com/captchas/recaptcha/v2_simple.php ^
-d "g-recaptcha-response=your_captcha_solution" ^
-d "other_data=value"
Example of using a proxy with the createTask request
If you want to send the request through a proxy, add the -x parameter:
MacOS/Linux:
curl -x http://proxy-server:port -X POST https://api.capmonster.cloud/createTask \
-H "Content-Type: application/json" \
-d '{
"clientKey": "API_KEY",
"task": {
"type": "RecaptchaV2TaskProxyless",
"websiteURL": "https://lessons.zennolab.com/captchas/recaptcha/v2_simple.php?level=high",
"websiteKey": "6Lcg7CMUAAAAANphynKgn9YAgA4tQ2KI_iqRyTwd"
}
}'
Windows (CMD):
curl -x http://proxy-server:port -X POST https://api.capmonster.cloud/createTask ^
-H "Content-Type: application/json" ^
-d "{\"clientKey\": \"API_KEY\", \"task\": {\"type\": \"RecaptchaV2TaskProxyless\", \"websiteURL\": \"https://lessons.zennolab.com/captchas/recaptcha/v2_simple.php?level=high\", \"websiteKey\": \"6Lcg7CMUAAAAANphynKgn9YAgA4tQ2KI_iqRyTwd\"}}"
cURL Debugging Output
This method is useful for checking how cURL sends a request through a proxy and whether it correctly interprets the settings.
- Use the --proxy flag to specify the proxy:
curl --proxy http://123.456.7.8.9:3128 http://example.com
If the proxy requires authentication, add:
curl --proxy http://user:password@123.456.7.8.9:3128 http://example.com
- Enable debug output with the -v or --trace-ascii flag:
curl -v --proxy http://123.456.7.8.9:3128 http://example.com
This will show connection details, sent headers, and other useful data.
- Check the result.
If the request is successful, you will see the HTTP response.
If there is an error (e.g., 407 Proxy Authentication Required), you can adjust the parameters.
Example with full trace output:
curl --trace-ascii debug.log --proxy http://123.456.7.8.9:3128 http://example.com
The output will be saved in the debug.log file for detailed analysis.
Using a local proxy server
This method is suitable for detailed checking of the data sent through the proxy (including headers, request body, responses, etc.).
- Set up and start a local proxy server:
mitmproxy --listen-port 8080
- Set up cURL to use a local proxy.
curl --proxy http://127.0.0.1:8080 http://example.com
- Open the mitmproxy interface to analyze requests.
You will be able to see all HTTP requests and responses in real-time.
This is useful for debugging to ensure that requests are being sent correctly and data is being routed through the proxy.
Additionally: connect a remote proxy through mitmproxy. If you want to use mitmproxy to monitor the interaction with a remote proxy, set it up as an "upstream proxy":
mitmproxy --mode upstream:http://123.456.7.8.9:3128 --listen-port 8080
To check the availability of the proxy itself, use the flags --connect-timeout and --max-time:
curl --proxy http://123.456.7.8.9:3128 --connect-timeout 10 --max-time 15 http://example.com
Like any program, cURL sometimes encounters errors. Here is a list of common errors when using cURL with a proxy and their possible causes:
- curl: (5) Unsupported proxy syntax. Incorrect proxy string format. Ensure that the proxy format is correct.
- curl: (7) Failed to connect to proxy_host port 8080: Connection refused. The proxy server is unavailable or turned off. Invalid IP address or port for the proxy. Check if the proxy is running and verify the IP and port.
- curl: (7) Could not resolve proxy: proxy_host. The specified proxy DNS name cannot be resolved. Ensure the hostname is correct. Try using the IP address instead of the hostname.
- curl: (35) schannel: next InitializeSecurityContext failed. SSL/TLS connection issues. Check if the proxy supports HTTPS. Temporarily disable certificate verification.
- curl: (52) Empty reply from server. The proxy did not send a response to the request. Check if the server is accessible via the proxy. Ensure your request is correct.
- curl: (56) Proxy CONNECT aborted. The proxy aborted the connection. Incorrect proxy credentials. Check the username and password for the proxy.
- curl: (407) Proxy Authentication Required. The proxy requires authentication, but credentials were not provided. Specify the username and password in the proxy string.
- curl: (28) Operation timed out. The proxy is unavailable. The server is taking too long to respond. Check the proxy and server availability. Increase the timeout.
- curl: (18) Transfer closed with outstanding read data remaining. The proxy unexpectedly closed the data transfer. Try a different proxy. Ensure the proxy supports the requested protocol (HTTP/HTTPS).
- curl: (22) The requested URL returned error: 403 Forbidden. Access to the resource via the proxy is blocked. Check if access to the target URL is allowed through the proxy. Use another proxy.
- curl: (60) SSL certificate problem. Issues with verifying the SSL certificate of the server. Disable SSL verification.
- curl: (6) Could not resolve host: example.com. The DNS name of the target server cannot be resolved through the proxy. Check the proxy's internet connection. Ensure the hostname is correct.
NB: Remember, the product is intended for automating testing on your own websites and websites you have lawful access to.