cURL: Invalid JSON when sending stdin as data

Question

I can control a Philips Hue light with the following command via cURL:

curl -X PUT --data '{"on":true}' "http://<bridgeip>/api/<key>/lights/7/state";

I am generating the payload with a function, so I wanted to pipe it to cURL (to take its input from stdin):

onString='{"on":true}';
echo "$onString" | curl -X PUT --data - "http://<bridgeip>/api/<key>/lights/7/state";

but this throws an error: "body contains invalid json"

What I don't get is that this works:

onString='{"on":true}';
curl -X PUT --data "$onString" "http://<bridgeip>/api/<key>/lights/7/state";

Can anyone explain please?

(Incidentally, when I pipe the output of my function to cat the resultant string is as expected and when copied and pasted into jsonlint checks out as valid JSON.)

hanshenrik · Accepted Answer · 2019-12-08 13:35:52Z

4

--data - doesn't fetch data from stdin, it just sends a literal - ,

to actually fetch data from stdin, use --data @-

(come to think of it, --data-binary @- is probably a better idea, i think it makes a difference with newlines when running on windows, but im not 100% sure)

answered Dec 8, 2019 at 13:35

hanshenrik

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4 Comments

Lorccan Over a year ago

That works. Thank you. It's confusing that the cURL man says: "If you start the data with the letter @, the rest should be a file name to read the data from, or - if you want curl to read the data from stdin."

Lorccan Over a year ago

I wanted to delete my question -even though you have been helpful- but some people have decided to start downvoting so I guess I'll just have to deal with it!

hanshenrik Over a year ago

@Lorccan any idea why you get downvotes? the only thing i'm conflicted on is "should this question be on stackoverflow.com or is it a superuser.com question?", but that doesn't warrant a downvote, at best it warrants a close/transfer vote

Lorccan Over a year ago

I can't see any reason, but then I asked the question! Not sure I get the distinction between stack overflow and superuser, so perhaps you're right.

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