Use curl -x (or --proxy) to send a request through an HTTP, HTTPS, or SOCKS proxy. Add -U for proxy credentials, choose --socks5 when DNS should resolve on your machine, and choose --socks5-hostname (or socks5h://) when the proxy should resolve the destination. Environment variables provide defaults, while --noproxy bypasses a proxy for selected hosts.
This guide covers command syntax, authentication, DNS behavior, tunneling, environment configuration, secret handling, troubleshooting, and a ready-to-run alternative for automated website captures.
Choose the proxy option that matches your connection
The proxy URL tells curl where to connect and which protocol to speak. If you omit a scheme, curl treats the proxy as HTTP.
| Use case | Command | What happens |
|---|---|---|
| HTTP proxy | curl -x http://proxy.example:8080 https://example.com |
curl connects to an HTTP proxy. For an HTTPS destination it normally requests a CONNECT tunnel. |
| HTTPS proxy | curl -x https://proxy.example:8443 https://example.com |
curl encrypts its connection to the proxy itself, then accesses the destination through it. |
| SOCKS5, local DNS | curl --socks5 proxy.example:1080 https://example.com |
Your machine resolves example.com; the proxy receives the resulting address. |
| SOCKS5, proxy DNS | curl --socks5-hostname proxy.example:1080 https://example.com |
The proxy resolves example.com. The equivalent URL form is socks5h://proxy.example:1080. |
--proxy and its short form -x accept http://, https://, socks4://, socks4a://, socks5://, and socks5h://. The proxy URL forms documented by curl use port 1080 when a SOCKS proxy port is omitted; specify the port explicitly to avoid ambiguity.
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Send a request through an HTTP or HTTPS proxy
Basic proxy request
curl -x http://proxy.example:8080 https://example.comThe explicit -x option takes precedence over proxy environment variables. Use the long form when documenting scripts for people who may not know curl’s short options:
curl --proxy https://proxy.example:8443 https://example.comRequest an HTTP CONNECT tunnel
For an HTTP proxy and an HTTPS destination, curl commonly uses the HTTP CONNECT method. If you need to request tunneling explicitly, add --proxytunnel:
curl --proxy http://proxy.example:8080 --proxytunnel https://example.comCONNECT establishes a tunnel through the HTTP proxy; it does not turn the proxy into a SOCKS server. Whether CONNECT is allowed is controlled by the proxy administrator.
Chain a SOCKS pre-proxy with an HTTP proxy
--preproxy lets curl reach an HTTP or HTTPS proxy through a SOCKS proxy:
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Authenticate to the proxy
Username and password
Proxy credentials belong in --proxy-user (short form -U), not in the remote-server-only authentication options:
curl --proxy http://proxy.example:8080
--proxy-user 'user:password'
https://example.comIf the password is omitted, curl can prompt for it interactively. This avoids putting the password directly in the command text:
curl --proxy http://proxy.example:8080 --proxy-user 'user' https://example.comQuote the value whenever it contains shell characters such as !, $, spaces, or a backslash. URL-encoding credentials inside a proxy URL is possible, but --proxy-user is clearer and avoids confusing URL parsing.
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Select the HTTP proxy authentication method
HTTP proxies can challenge with several methods. Use the method-specific flag when your administrator tells you which one is required:
--proxy-basic— HTTP Basic authentication (curl’s default HTTP proxy method).--proxy-digest— HTTP Digest authentication.--proxy-ntlm— NTLM authentication.--proxy-negotiate— Negotiate/SPNEGO authentication when curl and the environment support it.--proxy-anyauth— let curl discover and select a method supported by the proxy.
curl -x http://proxy.example:8080
-U 'user:password'
--proxy-digest
https://example.com--proxy-anyauth may require an extra request/response round trip while curl discovers the acceptable method. For predictable automation, selecting the known method is preferable.
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SOCKS authentication
SOCKS5 username/password authentication can be selected with --socks5-basic. Environments that provide GSS-API can use --socks5-gssapi:
curl --socks5 proxy.example:1080
--proxy-user 'user:password'
--socks5-basic
https://example.comSOCKS4 and SOCKS4a have different protocol capabilities; use the proxy type your server actually provides.
Understand SOCKS DNS resolution
--socks5: resolve locally
With --socks5 proxy:port, curl resolves the destination hostname locally before opening the SOCKS connection. This is useful when your local resolver is authoritative or when the proxy cannot resolve internal names. It also means the DNS query does not go through the SOCKS proxy.
--socks5-hostname and socks5h://: resolve through the proxy
With --socks5-hostname proxy:port, curl sends the hostname to the proxy and asks it to resolve the name. Use this when local DNS would leak a name, cannot reach a private DNS zone, or would return a different address than the proxy’s network.
curl --socks5-hostname proxy.example:1080 https://private.examplecurl -x socks5h://proxy.example:1080 https://private.exampleSOCKS4 versus SOCKS4a
--socks4 resolves locally and sends the address to the proxy. --socks4a asks the proxy to resolve the hostname. Pick the variant using the same local-versus-proxy DNS decision as SOCKS5.
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Set proxy defaults with environment variables
Environment variables are convenient for shells, CI jobs, and applications that invoke curl repeatedly:
http_proxy— default proxy for HTTP URLs.HTTPS_PROXY— default proxy for HTTPS URLs.FTP_PROXY— default proxy for FTP URLs.ALL_PROXY— general fallback proxy.NO_PROXY— hosts and domains that should not use a proxy.
export http_proxy=http://proxy.example:8080
export HTTPS_PROXY=http://proxy.example:8080
export ALL_PROXY=socks5h://proxy.example:1080
export NO_PROXY=localhost,127.0.0.1,.internal.example
curl https://example.comA leading dot in NO_PROXY, such as .internal.example, matches that domain and its subdomains. Environment variable names are case-sensitive on many Unix-like systems; set the spelling expected by your environment. An explicit -x/--proxy on the command line overrides the environment defaults.
Bypass the proxy for one command
Use --noproxy when the exception should apply only to one invocation:
curl --noproxy 'localhost,127.0.0.1,.internal.example'
-x http://proxy.example:8080
https://example.comTo bypass proxying for every host in that command, use --noproxy '*'. Check inherited NO_PROXY values if a request unexpectedly avoids the proxy.
Protect proxy credentials
Command-line arguments can be visible to other users through process-listing tools. Although curl may briefly hide an option argument on systems where that is supported, do not treat the command line as a secret store.
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- Prompt interactively by supplying only the username with
--proxy-user. - Use a protected configuration file or your CI platform’s secret mechanism for unattended jobs.
- Restrict file permissions and avoid committing proxy URLs containing credentials to source control.
- Do not paste credentials into verbose logs, support tickets, or shell history.
When a proxy password contains characters meaningful to your shell, quote it or provide it through the protected mechanism rather than trying to debug shell expansion.
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Add -v to inspect proxy selection, the CONNECT exchange, TLS negotiation, and authentication challenges:
curl -v -x http://proxy.example:8080 https://example.comVerbose output can include headers and sensitive values. Review it before sharing. Use -I for a headers-only test when the server supports HEAD, or use --trace-time with a protected trace file when timing details are needed.
Common errors and fixes
| Symptom | Likely cause | Fix |
|---|---|---|
| Unsupported proxy scheme | The URL uses a scheme curl does not recognize or a typo in the scheme. | Use one of http://, https://, socks4://, socks4a://, socks5://, or socks5h://. |
| Could not resolve proxy | The proxy hostname or local DNS is wrong. | Verify the proxy name, port, and local resolver; test with -v. |
| 407 Proxy Authentication Required | The proxy requires credentials or a different HTTP authentication method. | Add -U and select --proxy-basic, --proxy-digest, --proxy-ntlm, --proxy-negotiate, or --proxy-anyauth as appropriate. |
| SOCKS connection succeeds but hostname fails | DNS is happening on the wrong side of the proxy. | Switch between --socks5 and --socks5-hostname (or socks5h://). |
| HTTPS request rejected at CONNECT | The HTTP proxy disallows tunneling to that destination or port. | Ask the proxy administrator to permit CONNECT, or use a permitted proxy/protocol. |
| Request unexpectedly goes direct | NO_PROXY or --noproxy matches the host. |
Inspect and adjust the bypass list, then retest with -v. |
| Authentication loops or adds delay | Automatic method discovery is negotiating repeatedly. | Replace --proxy-anyauth with the known method-specific flag. |
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A proxy adds at least one network hop and, for HTTP proxies serving HTTPS destinations, a CONNECT negotiation. SOCKS proxy-side DNS can avoid an unreachable local resolver but depends on the proxy’s DNS service. Reuse a single curl process for multiple URLs when possible, and keep proxy settings in a controlled environment rather than rebuilding them inconsistently per request.
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Quick decision checklist
- Use
-x http://...for a standard HTTP proxy and-x https://...when the proxy connection itself must use TLS. - Use
--proxy-userfor proxy credentials and select the authentication method that the proxy advertises. - Choose
--socks5for local DNS or--socks5-hostname/socks5h://for proxy-side DNS. - Use environment variables for defaults and
--noproxyfor a one-command exception. - Run with
-vwhile diagnosing, but redact credentials and sensitive headers before sharing logs.
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