Curl error: Unsupported proxy syntax

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Situation

The system has a proxy enabled. When executing a curl command, the following error message is displayed:
url: (5) Unsupported proxy syntax in '127.0.0.1:8899

Resolution

Check the proxy configuration file (/etc/sysconfig/proxy) and the proxy environment variables for syntax errors.

Some characters might not be easily visible on the terminal. Consider making a hex dump of the proxy environment variables for better visibility:

echo "$http_proxy" | xxd
00000000: 3132 372e 302e 302e 313a 3838 3939 0d0a  127.0.0.1:8899..

echo "$https_proxy" | xxd
00000000: 3132 372e 302e 302e 313a 3838 3939 0d0a  127.0.0.1:8899..

In this example, both the http_proxy and https_proxy environment variables contain an extra 0d (\r or carriage return). Carriage return is a line delimiter used in DOS/Windows ASCII text, but not in Linux or Unix.

Carriage returns can be removed from a file with the command:

dos2unix <filename>

Unexpected characters can also be manually removed with the backspace or delete keys, even if you cannot see them. A full line can be deleted and retyped.

Cause

The cause of this issue is an invalid syntax in the proxy string.

Additional Information

Reference:
* https://www.suse.com/support/kb/doc/?id=000017441
* man curl

Disclaimer

This Support Knowledgebase provides a valuable tool for SUSE customers and parties interested in our products and solutions to acquire information, ideas and learn from one another. Materials are provided for informational, personal or non-commercial use within your organization and are presented "AS IS" WITHOUT WARRANTY OF ANY KIND.