How to use cURL With a Proxy

Article’s Key Takeways

• cURL is a versatile command-line tool that allows you to transfer data over different protocols, and pairing it with proxies adds flexibility for testing, privacy, and working around network restrictions.
• You can configure cURL to use HTTP/HTTPS or SOCKS proxies via command-line flags, environment variables, or configuration files, with options for authentication when required. It also supports bypassing proxies for specific hosts and quick on/off switching, making it practical for both one-off requests and persistent setups. 
• Mastering these configurations ensures you can troubleshoot effectively, access restricted resources, and maintain privacy while using cURL across different systems.

What is cURL and Why use It?

cURL is a command-line utility that uses URLs to move data between network protocols. You can quickly download files from a terminal or in scripts because it can use various protocols, including HTTP and HTTPS. Due to its speed and versatility, cURL is frequently used in command lines. The fact that cURL also supports using tunneling servers is a useful feature. This implies that you can use an intermediary proxy to route your http requests. (If no protocol is supplied, cURL will use HTTP as the default protocol. When you need to cope with network constraints (such as a firewall), you wish to use a proxy to improve privacy by disguising your IP or want to test how requests behave from different places, running cURL with a proxy has its uses. Put simply, curl turns any terminal into a lightweight API client.

How to Install cURL

Check that cURL is already on your machine before you use it, with or without a proxy. For the most common operating systems, the following startup instructions are not sufficient:
See more:

Windows: 

10 and 11 come with cURL already installed. Run curl –version to verify. You can use a  package manager like Chocolatey (choco install curl) or Scoop (scoop install curl) to set up or update it, or you can download the original curl binary and add it to your PATH.

macOS: 

cURL is already installed on macOS (use curl –version to see). You can use Homebrew (brew install curl) to get the latest version and then make sure your PATH finds the version that Homebrew loaded.

Linux: 

Most versions of Linux come with cURL already installed (use curl –version to check). You can use your package manager to install it if it’s not already there: sudo apt set up curl on Debian/Ubuntu or sudo dnf install curl on Fedora. You can use curl from any shell. Now curl is available system-wide for every user. The curl tool can be used right away in the terminal after it has been installed. You can freely use this approach in any shell script that calls cURL.
Getting ready to use proxies with cURL.

Preparing to use Proxies with cURL

When preparing to use proxies with cURL, set up the necessary proxy details first:

• Proxy Address: The hostname or IP address of the intermediary server (e.g., proxy.example.com or an IP address).
• Port: The port number on which the proxy runs (common ports are 3128, 8080, etc.).
• Proxy Type: The protocol of the proxy – usually HTTP/HTTPS or SOCKS4/SOCKS5. (cURL needs to know this to form the correct connection.)
• Authentication Details: You need to use username and password if the proxy requires user authentication (not all proxies need a login, but many corporate proxies do).

Setting Up an HTTP/HTTPS Proxy

Once you have the proxy info, you can use it with cURL in a couple of ways. The simplest is to set up the proxy on the command line for a single request. The curl proxy command to do this is -x (or –proxy). You provide the proxy URL (including the port, and optionally the scheme and credentials). For example:

curl -x http://proxy.example.com:8080 http://example.com

In this curl proxy example, cURL will send the request to example.com through the proxy at proxy.example.com:8080. Here, curl using proxy is demonstrated by the fact that the request goes through the proxy before reaching the target. This curl proxy command tells cURL to route the request via that proxy server. If your proxy requires you to use a username and password, you can include them in the proxy URL (for example, http://user:password@proxy.example.com:8080) or use the –proxy-user user:password option. Remember to use verbose mode (-v) if you need to debug the proxy handshake. For an HTTPS proxy (a proxy that requires an SSL connection), you would use an https:// URL for the proxy. The usage is similar: cURL will handle connecting to the secure proxy and then relay your HTTPS request.

Another method is setting environment variables to set up a proxy globally. Most teams make use of environment variables to keep proxy credentials out of scripts. (for example, export http_proxy=”http://proxy.server:8080″ on Linux/Mac or set http_proxy=http://proxy.server:8080 on Windows). After this, cURL will automatically use that proxy for all HTTP requests — once it’s set up, you can proceed.” (essentially every command becomes curl with proxy by default) until you change or unset those variables. Environment-based configuration is an easy way to set curl proxy when you always need the gateway enabled. Just remember to unset or change these variables when you want to stop using the proxy.

Using SOCKS4/SOCKS5 Proxies with cURL

cURL can also work with SOCKS type proxies. To use a SOCKS4 or SOCKS5 proxy, you set up it similarly but with a different flag or scheme. Developers often use a local SOCKS5 proxy while testing mobile apps on an emulator. For example, to use a SOCKS5 proxy on localhost port 1080:

curl --socks5 localhost:1080 http://example.com

This tells cURL to route the HTTP request through a SOCKS5 proxy running at localhost. You can do the same with –socks4 for a SOCKS4 proxy. Alternatively, using the -x option, set up the scheme in the proxy URL:

curl -x socks5h://localhost:1080 http://example.com

In this case, socks5h tells cURL to use a SOCKS5 proxy and to perform DNS resolution through the gateway (the socks protocols allow the proxy to handle DNS if the h flag is used). SOCKS4 proxies are older and don’t support authentication or IPv6, whereas SOCKS5 supports various features including user authentication. If the proxy needs a login, provide credentials just like with an HTTP proxy (using –proxy-user). With socks proxy support, cURL gives you flexibility to route traffic through different kinds of intermediary servers. cURL supports both SOCKS4 and SOCKS5, so it can work with these different protocols of proxies as easily as with HTTP proxies.

Methods to Set Proxies in cURL

There are several methods to set up a proxy for cURL. You can do it per command, via environment, or with a config file. Here are the different ways:

Command-Line Options

The first method is using command-line flags each time you run cURL. As mentioned, the primary flag is -x (or –proxy) followed by the proxy URL. You can include credentials if needed (for example, –proxy http://user:pass@proxy.company.com:8080). You can also add –noproxy in the command to exclude certain hosts for that particular request (more on –noproxy below). Command-line options give precise control on a per-request basis. When performance matters, use the –parallel flag together with your proxy settings. If you don’t want to always use an intermediary server, this method lets you set when to use it by specifying the proxy only when needed.

Environment Variables

Another method is setting environment variables to set a proxy globally. For scripted jobs, you can preload these variables before any curl step runs. For example, you can set http_proxy=”http://user:pass@proxy.company.com:8080″ (and similarly https_proxy). The same syntax applies to curl –proto if you need to limit allowed schemes. After this, cURL will automatically use that proxy for all HTTP requests. Internally, curl reads the variable once per new transfer, so changes apply immediately. This environment-based approach acts as a persistent curl proxy setting for your session. You can also combine it with CURL_CA_BUNDLE to force curl to trust a custom root CA. Setting CURL_HOME lets curl isolate config files when you automate across user accounts. It is easy when you always need the proxy enabled. Just remember to unset or change these variables when you no longer want cURL to use the proxy. A quick unset http_proxy https_proxy returns curl to a direct-connect state. If you require granular control, prefix a single command with http_proxy= to make curl pick a one-off proxy without touching global variables.

Persistent Configuration Files

The third method is to use cURL’s configuration file to set aside the proxy settings permanently. On Linux/macOS, this file is ~/.curlrc (and on Windows, _curlrc in the user profile). You can add your proxy details there – for example:

proxy = http://proxy.company.com:8080
proxy-user = username:password

After that, every time you run cURL it will use that proxy by default. It’s a way of storing a persistent curl proxy setting in your environment. If you need to bypass it occasionally, run curl -q to prevent cURL from loading the config file for that run. This method is handy if you always need an intermediary serverenabled (such as on a corporate network). Just be sure to set up the config file secure if it contains login info.

How to Bypass or Disable Proxy for Specific Requests

Even if you have a proxy configured, you may want to skip it for certain destinations. For example, you might not want to send requests for local hosts or an internal server through the gateway. One way to bypass the proxy on a per-request basis is using the –noproxy option in your cURL command. With –noproxy, you set up a list of hostnames that should not go through the proxy. For example:

curl --noproxy example.com,localhost http://example.com

This tells cURL not to use the proxy for any host matching example.com or localhost in that command. You can use * as a wildcard (or –noproxy ‘*’) to disable the proxy for that single request entirely.

Another way is to set the NO_PROXY environment variable (or no_proxy) with domains or IP addresses that should be accessed directly. For example:

export NO_PROXY="localhost,127.0.0.1,.internal.example.com"

Once this is set, any curl requests to hosts that match those patterns will skip the proxy. This is useful for addressing scenarios where some addresses should be reached directly even though a proxy is generally in use. You can combine this with the earlier environment variables to fine-tune what goes through the intermediary server and what doesn’t. Essentially, NO_PROXY lets you maintain a list of exceptions so that you use the proxy for most requests but not for certain domains.

Quick Proxy On/Off Switching

While using cURL, you may need to quickly turn on or off proxy use. Here are some tips that will save you time from having to change configurations every time:

• Shell aliases or scripts: To change your environment intermediary server settings, use shell aliases or short scripts. You could make an alias proxy_on to export your http_proxy and httpss_proxy variables, and another alias proxy_off to unset them. That way, typing one or the other before your cURL commands makes it easy to switch. You can then set whether to use curl with proxy. For quick checks, simply use curl ifconfig.me through the proxy to see the exit IP.
• Ignoring config for one run: If your cURL configuration file (.curlrc) sets up a intermediary server, remember that you can run curl -q… to skip that file for one call. This quick option stops cURL from using the default configuration. This lets you run a command without the intermediary server (without having to change your configuration file).
• Alternate config for proxies: On the other hand, if you usually don’t need a proxy when you run curl, you could write a small wrapper or use the -K option to point to a file that has proxy settings. For example, use curl -K proxy.cfg “http://example.com” with the file proxy.cfg holding your information. Instead of typing in the proxy information every time, this makes it easy to turn it on when you need to.
  You can change your settings at any time with these ways. It saves time and keeps you from sending traffic in the wrong direction by mistake. You can avoid typing long proxy addresses repeatedly or forgetting to turn off the intermediary server when it’s not needed with a little bit of set up.

Choosing the Right Proxy for cURL

Not every proxy is created equal. When choosing a intermediary server to use with cURL, consider the following factors:

• Type (SOCKS vs. HTTP): use a SOCKS5 for different protocols or if you want the proxy to perform DNS lookups. use HTTP for regular web traffic (HTTP/HTTPS). Set the type that best suits your needs from the two that cURL supports.
• Location/IP: Use a server in the target nation if you need to access geoblocked material. To cycle across different IP addresses for testing or scraping, you may use a residential proxy service or rotating proxy. If you are willing to pay, paid proxies are typically more trustworthy.
• Performance: Latency may be introduced by proxy. Reduce delays by using a quick, low-latency proxy. Your curl commands will execute nearly as fast with a good intermediary server as they would with a direct connection. Timing a few curl requests with and without the proxy allows you to assess performance.
• Privacy: Use proxies that conceal your information if privacy is vital. Always use HTTPS proxies when transmitting sensitive tokens or API keys. For data protection, an HTTPS proxy is more secure than an HTTP proxy. Because a proxy server can view the content of unencrypted HTTP traffic, only use proxies you trust for sensitive data. When utilizing curl through an unreliable proxy, exercise caution.
• Authentication: use the right credentials If the proxy is requiring authentication. use the –proxy-user option, for instance, or set up proxy:p as s@ in the proxy URL if the proxy needs to be logged in. cURL supports a variety of authentication techniques (Basic, NTLM, etc.), therefore providing the necessary credentials guarantees that it works with whatever your proxy needs.
• Reliability: For important or time-consuming tasks, use a stable and trustworthy proxy. Free proxies may be unreliable or slow; for serious use, look for commercial services with a high uptime rate. Additionally, see if there are any restrictions or data limits. Always include a fallback alternative to ensure that your workflow isn’t interrupted if a proxy fails.

With these curl patterns in mind, troubleshooting intermediary server issues becomes straightforward. Whichever path you choose, curl remains consistent across Unix-like systems.

Conclusion

Working in a variety of network environments requires the ability to use curl with proxy servers. This article explained what cURL is, why proxies are useful, how to set up curl on Windows, macOS, and Linux, as well as different ways of set up curl to use proxies. We examined how to set up an HTTP/HTTPS proxy, how to use SOCKS proxies, how to change proxy settings using environment variables and configuration files, and how to bypass the intermediary server when necessary. We also covered how to easily turn proxy use on or off as well as factors to consider when selecting a suitable intermediary server for your needs. After updating cURL, make use of –help to review any new proxy-related flags. You ought to feel at ease configuring curl to route traffic either directly or through an intermediary server as necessary. Depending on your needs and use cases, you can therefore safely run curl with proxy or without.