mjhjmtu

The following curl command works as expected:

$ curl -H @- -vso/dev/null http://www.example.com <<<"Foo:Bar"
* Rebuilt URL to: http://www.example.com/
...
> Accept: */*
> Foo:Bar
> 
< HTTP/1.1 200 OK
...

since I can see my custom header (Foo:Bar), but it doesn't work when running via ssh:

$ ssh user@localhost curl -H @- -vso/dev/null http://www.example.com <<<"Foo:Bar"
* Rebuilt URL to: http://www.example.com/
...
> Accept: */*
> 
< HTTP/1.1 200 OK
...

I can confirm that the stdin works on the remote by:

$ ssh user@localhost cat <<<"Foo:Bar"
Foo:Bar

My goal is to pass the headers from stdin or local file (not from the variable) into remote curl.

And I'm not quite sure why the above doesn't work.

The argument in @filename style for -H has been added in 7.55.0 (man curl).

-H/--header <header/@file>

Starting in 7.55.0, this option can take an argument in @filename style, which then adds a header for each line in the input file. Using @- will make curl read the header file from stdin.

The problem with ssh happened because older curl version was used.

So basically two different versions of curl were involved.

$ which curl && curl --version
/usr/local/bin/curl
curl 7.59.0 (x86_64-apple-darwin17.3.0) libcurl/7.59.0 OpenSSL/1.0.2o zlib/1.2.11 libidn2/2.0.4
$ ssh user@localhost 'which curl && curl --version'
/usr/bin/curl
curl 7.54.0 (x86_64-apple-darwin17.0) libcurl/7.54.0 LibreSSL/2.0.20 zlib/1.2.11 nghttp2/1.24.0

So hardcoding the path to newer /usr/local/bin/curl (v7.59/OpenSSL) it seems to work fine:

$ ssh user@localhost /usr/local/bin/curl -H @- -vso/dev/null http://www.example.com <<<"Foo:Bar"