The cURL command-line tool is an indispensable utility for developers, system administrators, and web scrapers. It allows you to transfer data to or from a server using various protocols, making it perfect for testing APIs, debugging network issues, and performing automated data requests.
However, when performing high-volume requests or accessing geo-restricted content, sending requests directly from your machine's IP address can quickly lead to rate limits, blocks, or IP bans. The solution is to route your cURL requests through a proxy server.
This comprehensive guide will walk you through all the necessary steps and commands to effectively use cURL with a proxy, ensuring your operations remain anonymous, successful, and unrestricted. We will use Nstproxy as the example provider, as their robust proxy infrastructure is perfectly suited for high-performance cURL tasks.
What is cURL and Why Use a Proxy?
cURL (Client URL) is a command-line tool and library for transferring data with URLs. In its simplest form, it fetches the content of a web page:
curl https://www.google.com
When you use cURL without a proxy, the request originates from your computer's public IP address. A acts as an intermediary, forwarding your request to the target server and receiving the response on your behalf.
Bypassing Restrictions: Overcoming geo-blocks, network firewalls, and IP-based rate limits.
Web Scraping: Distributing requests across a pool of IPs (like Nstproxy's Residential Proxies) to avoid detection.
Required Proxy Connection Details
Regardless of which proxy provider you choose, you will need the following information to configure cURL to use a proxy:
Proxy Server Address: The hostname or IP address of the proxy server (e.g., proxy.nstproxy.io).
Port: The port number the proxy server is listening on (e.g., 12345).
Protocol: The type of proxy (e.g., HTTP, HTTPS, SOCKS5).
Authentication: Username and password (if required by the proxy provider).
For all examples in this guide, we will use the following placeholders:
Proxy Host:proxy.nstproxy.io
Port:24125
Username:nstuser
Password:nstpwd
Test URL:https://ipinfo.io (This URL will return the IP address seen by the server, which should be the proxy's IP).
Method 1: Using the Command-Line Argument (-x or --proxy)
The most common and flexible way to use a proxy with cURL is by passing the proxy details directly as a command-line argument using the -x or --proxy flag.
HTTP and HTTPS Proxies
The syntax for an authenticated HTTP proxy is to include the protocol, credentials, host, and port in the proxy string:
[protocol]://[username]:[password]@[host]:[port]
The following commands are functionally identical and route the request through the proxy:
# Using the short form -xcurl-x"http://nstuser:nstpwd@proxy.nstproxy.io:24125 "https://ipinfo.io"
# Using the long form --proxy
curl --proxy "http://nstuser:nstpwd@proxy.nstproxy.io:24125 "https://ipinfo.io"
Note on Protocols:
If your proxy server uses the HTTPS protocol, simply change the protocol prefix in the proxy string:
For repeated use, especially in shell scripts or when you want to set a system-wide proxy for all cURL requests, you can use environment variables. This method is supported on Linux and macOS.
The two main variables are http_proxy and https_proxy. They define the proxy to be used for target URLs starting with http:// and https://, respectively.
# 1. Set the environment variablesexporthttp_proxy="http://nstuser:nstpwd@gate.nstproxy.io:24125"exporthttps_proxy="http://nstuser:nstpwd@proxy.nstproxy.io:24125"# 2. Run cURL normally (the proxy is automatically used)curl"https://ipinfo.io"
To disable the global proxy settings, simply unset the variables:
unset http_proxy
unset https_proxy
Method 3: Configuring cURL to Always Use a Proxy (.curlrc)
If you want a persistent proxy setting that only affects cURL and not other programs on your system, you can use the cURL configuration file.
Locate/Create the File:
Linux/macOS: Create or edit the file named .curlrc in your home directory (~/.curlrc).
Windows: Create or edit the file named _curlrc in the %APPDATA% directory.
Add the Proxy Line: Add the following line to the configuration file:
Run cURL: Now, any time you run cURL without specifying a proxy, it will automatically use the one defined in the configuration file:
curl"https://ipinfo.io"
Method 4: Using cURL with SOCKS Proxies
SOCKS proxies (SOCKS4, SOCKS5) are often preferred for their flexibility as they operate at a lower level than HTTP proxies. cURL supports SOCKS proxies using the -x flag with the appropriate protocol prefix (e.g., socks5://).
SOCKS Proxy with -x Flag
# Using the -x flag with SOCKS5 protocolcurl-x"socks5://nstuser:nstpwd@proxy.nstproxy.io:12345 "https://ipinfo.io"
SOCKS Proxy with --socks5 Flag
Alternatively, you can use the dedicated --socks5 flag and pass the authentication separately using --proxy-user:
# Using the dedicated --socks5 flagcurl--socks5"proxy.nstproxy.io:24125 "https://ipinfo.io" --proxy-user nstuser:nstpwd
Bonus Tip: Overriding or Ignoring Proxy Settings
If you have a global proxy set (via environment variables or .curlrc) but need to bypass it for a single request, you can use the --noproxy flag.
# Bypass proxy for all URLscurl--noproxy"*""https://ipinfo.io"# Override global proxy with a different one for a single requestcurl--proxy"http://newuser:newpwd@1.0.0.1:8090""https://ipinfo.io"
Conclusion: Why Nstproxy is the Best Choice for cURL
cURL is a powerful tool, and its effectiveness is directly tied to the quality of the proxy server it connects to. For web scraping, API testing, and data collection, a reliable proxy provider is non-negotiable.
Nstproxy is the best proxy provider for cURL integration because we offer:
Massive IP Pool: Access to millions of Residential and Datacenter IPs, ensuring your requests are distributed and never blocked.
High Reliability: Our proxies are built for high-volume, high-concurrency tasks, guaranteeing a high success rate for your cURL operations.
Flexible Protocols: Full support for HTTP, HTTPS, and SOCKS5 protocols, allowing you to use the exact cURL command that fits your needs.
By using the commands outlined in this guide with Nstproxy's robust infrastructure, you can execute your data transfer tasks with speed, anonymity, and confidence.
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Q1: What is the difference between the -x and --proxy flags in cURL?
A: There is no functional difference. Both -x (short form) and --proxy (long form) are used to specify the proxy server address and protocol. The choice between them is purely a matter of preference.
Q2: What is the default port for a cURL proxy if I don't specify one?
A: If you omit the port number in the proxy string, cURL will use a default port based on the specified proxy protocol:
Protocol
Default Port
HTTP
1080
SOCKS4/SOCKS5
1080
HTTPS
443
Q3: How can I verify that my cURL request is using the Nstproxy IP?
A: You can verify the proxy is working by sending a request to an IP check service. Using the test URL from this guide:
The output will be the IP address of the Nstproxy server, confirming that your request was successfully routed through the proxy.
Q4: Should I use HTTP or SOCKS5 proxies with cURL?
A:HTTP proxies are generally simpler and faster for basic web requests. SOCKS5 proxies are more versatile as they can handle any type of traffic (not just HTTP) and operate at a lower network layer. For complex web scraping or non-HTTP protocols, SOCKS5 is often the better choice. Nstproxy supports both, allowing you to choose the best option for your task.
Q5: What is the no_proxy environment variable?
A: The no_proxy environment variable allows you to specify a comma-separated list of domain suffixes, IP addresses, or hostnames that should not be accessed via a proxy server, even if a global proxy is set. This is useful for accessing local network resources while keeping external traffic proxied.
Lena Zhou
Feb. 3rd 2026
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