use pipe for curl data

I'm trying to pass the cat output to curl:

$ cat file | curl --data '{"title":"mytitle","input":"-"}' http://api

But input is literally a -.

I spent a while trying to figure this out and got it working with the following:

cat data.json | curl -H "Content-Type: application/json" -X POST --data-binary @- http://api

You can use the magical stdin file /dev/stdin

cat data.json | curl -H "Content-Type: application/json" -X POST -d "$(</dev/stdin)" http://api

This should also work

curl -H "Content-Type: application/json" -d @data.json http://api

Using -d forces curl to implicitly use POST for the request.

# Create the input file
echo -n 'Try 😁 and " to verify proper JSON encoding.' > file.txt

# 1. Use jq to read the file into variable named `input` 
# 2. create the desired json
# 3. pipe the result into curl
jq -n --rawfile input file.txt '{"title":"mytitle", $input}' \
| curl -v 'https://httpbin.org/post' -H 'Content-Type: application/json' -d@- 

Output:

  ...
  "json": {
    "input": "Try \ud83d\ude01 and \" to verify proper JSON encoding.", 
    "title": "mytitle"
  }, 
  ...

Notice that the contents of the input file was properly escaped for using as a JSON value.

jq options used:

• --null-input/-n:
  Don’t read any input
• --rawfile variable-name filename:
  This option reads in the named file and binds its contents to the given global variable.

See jq manual for full details.

The -d@- option tells curl to read the data from STDIN.

If you want to type/paste the data without escaping or polluting your bash history then, you can use this

cat | curl -H 'Content-Type: application/json' http://api -d @-

Which drops you into cat where you can input the data, directly, e.g. Shift + Insert in your terminal. You finish with a newline and a Ctrl + D which signals to cat that you're done. That data is then passed to curl, and you have a reusable history entry.

Try

curl --data '{"title":"mytitle","input":"'$(cat file)'-"}' http://api

Curl documentation for -d option >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. Multiple files can also be specified. Posting data from a file named 'foobar' would thus be done with -d, --data @foobar. When --data is told to read from a file like that, carriage returns and newlines will be stripped out. If you don't want the @ character to have a special interpretation use --data-raw instead.

Depending of your HTTP endpoint, server configuration, you should be good by using this format:

curl -d @data.json http://api

Sounds like you want to wrap the content of input in a JSON body, and then have that sent over with a POST request. I think that the simplest way to do that is to manipulate stdin first and then push that over to curl using -d @-. One way could look like this:

cat <(echo '{"title":"mytitle","input":"') file <(echo '"}') \
| curl -d @- http://api

I'm using <(echo) to use cat to merge strings and files, but there is almost certainly a better way.

Keep in mind that this does not escape the contents of file and that you may run into issues because of that.