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I noticed that I am able to pass JSON with this command

command -j /dev/stdin <<< '{"key":"value"}'

However, it does not work if I call it through SSH.

ssh {target} 'command -j /dev/stdin <<< '{"key":"value"}''

Looks like it send through as a string and not JSON? Anyone have any idea why?

I have a command where I need to pass a JSON string to the options but for some reasons I need it to be passed using herestring to /dev/stdin.

Example

command -j /dev/stdin <<< '{"key":"value"}'
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  • Your problem are the unescaped single quotes. You have ' before command that is closed after <<<```. I think you need to use \'`` after <<< and after "value"}. Otherwise you close the ssh single quotes at the first inner single quote and open it again at the second one. Commented Jul 26, 2019 at 11:45

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There is no need to make the here-string redirection part of the remote command. Data redirected into ssh would end up on the standard input of the remote command:

ssh remote 'some command' <<<'whatever string'

In your case,

ssh target 'command -j /dev/stdin' <<<'{"key":"value"}'

But this assumes that both key and value are already JSON encoded.

Constructing the JSON with jq (to get proper encoding of the value, assuming it is held in a shell variable $value):

jq -nc --arg val "$value" '{ key: $val }' | ssh target 'command -j /dev/stdin'

Or, use jo to write the JSON document:

jo key="$value" | ssh target 'command -j /dev/stdin'
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I figured it out, when passing " to SSH I would need to use \\\" to let it go through. So the command below works.

ssh {target} 'command -j /dev/stdin <<< '{\\\"key\\\":\\\"value\\\"}''
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  • Note that this would possibly not JSON encode the strings in the JSON document. Commented Jun 28, 2021 at 9:53

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