How to run command over ssh without clobbering stdin for subsequent curl command?

Question

This bash script is supposed to fetch a token from elsewhere via ssh, then run a curl command where it reads data from a file on stdin.

#!/usr/bin/env bash
TOKEN=$(ssh somewhere cat sometoken.txt)
curl https://example.com \
  -H "Authorization: Bearer $TOKEN" \
  -H "someparam=@-" \
  -X POST

And the script is called like this:

cat somefile | myscript

When I hardcode TOKEN=abcd123 instead of using $(ssh ...), somefile is uploaded as expected by curl.

However when I use $(ssh ...) my file is not uploaded.

I assume that my script's stdin is being clobbered by $(ssh ...) but I can't see how to work around that.

Any help would be much appreciated.

Answer 1

In short, use ssh -n ...

The ssh tool reads all data from standard input. It does this to be able to pass it on to any command that you are executing on the remote side (you could use ssh remote 'cat >out' <in to copy the contents of a file to a remote system if you so wished).

With its -n option, you tell it to not do that. It would be more or less equivalent to redirecting /dev/null into its standard input by doing ssh ... </dev/null.