[vesinisa]

curl -H/--header itself also takes a file name prefixed by @, including - for stdin. So you could go curl -H@- <<<'API-Key: Foobar', or if you need to specify multiple sensitive headers, curl -H@<(echo API-Key: Foo) -H@<(echo Pre-Shared: Bar)

[remram]

<() is a bash extension and won't work in another `sh` like dash.