| Long: proto | 
 | Arg: <protocols> | 
 | Help: Enable/disable PROTOCOLS | 
 | See-also: proto-redir proto-default | 
 | Added: 7.20.2 | 
 | --- | 
 | Tells curl to limit what protocols it may use in the transfer. Protocols are | 
 | evaluated left to right, are comma separated, and are each a protocol name or | 
 | 'all', optionally prefixed by zero or more modifiers. Available modifiers are: | 
 | .RS | 
 | .TP 3 | 
 | .B + | 
 | Permit this protocol in addition to protocols already permitted (this is | 
 | the default if no modifier is used). | 
 | .TP | 
 | .B - | 
 | Deny this protocol, removing it from the list of protocols already permitted. | 
 | .TP | 
 | .B = | 
 | Permit only this protocol (ignoring the list already permitted), though | 
 | subject to later modification by subsequent entries in the comma separated | 
 | list. | 
 | .RE | 
 | .IP | 
 | For example: | 
 | .RS | 
 | .TP 15 | 
 | .B --proto -ftps | 
 | uses the default protocols, but disables ftps | 
 | .TP | 
 | .B  --proto -all,https,+http | 
 | only enables http and https | 
 | .TP | 
 | .B --proto =http,https | 
 | also only enables http and https | 
 | .RE | 
 |  | 
 | Unknown protocols produce a warning. This allows scripts to safely rely on | 
 | being able to disable potentially dangerous protocols, without relying upon | 
 | support for that protocol being built into curl to avoid an error. | 
 |  | 
 | This option can be used multiple times, in which case the effect is the same | 
 | as concatenating the protocols into one instance of the option. |