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.