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I want to do an HTTP POST of the contents (as a string) of a local file located at path/to/my-file.txt to a URL endpoint at http://example.com/.

For example, I might want to do the following:

  1. Extract the contents of the file my-file.txt as a string.
  2. URL encode the string.
  3. Store the encoded string as a variable named foo.

Then do something like this:

curl -d "data=foo" http://example.com/

(I don't actually need the foo variable. It's just a convenient way to describe my question.)

What are the commands I would need to execute this? Do I need to write a shell script? If so, how might it look?

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3 Answers 3

Reset to default
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According to the last section of -d in man curl:

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 --data @foobar. When --data is told to read from a file like that, carriage returns and newlines will be stripped out.

That is you don't have to do anything fancy just prepend your filename with a @.

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  • 3
    And if you want some useful shell escaping (eg. to use jq to preprocess some JSON, try: curl ... -d @<(jq '{"schema": . | tostring }' myschema.avsc') Use-case: wrap a JSON document into a string of another JSON document to pass it to a REST API. (Confluent Schema Registry)
    – Cameron Kerr
    Jun 15, 2018 at 0:14
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    Also keep in mind that if you're uploading binary files, you should use --data-binary.
    – ahmet alp balkan
    Aug 7, 2019 at 0:18
  • how can we post data from a url?
    – Jus12
    Feb 19, 2021 at 12:00
  • PLEASE How can I stop stripping line endings from the file input? I need it because of elasticsearch bulk format needs to ended with new line.
    – Čamo
    Jul 1, 2021 at 14:27
  • @Čamo See the comment of Ahmet
    – gkephorus
    Nov 1, 2021 at 11:39
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As mentioned in this related question if you want the file uploaded without any changes (curl defaults to stripping carriage-return/line-feed characters) then you may want to use the --data-binary option:

curl -X POST --data-binary @path/to/my-file.txt http://example.com/
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  • But I need to send application/json but with line endings
    – Čamo
    Jul 1, 2021 at 14:28
  • I need it because of Elasticsearch _bulk api and the solution is to send header Content-Type: application/x-ndjson
    – Čamo
    Jul 1, 2021 at 17:53
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To be explicitly clear, the accepted answer suggests:

curl -d "data=@path/to/my-file.txt" http://example.com/

The manual reference is here.

Also see this SE answer and this one also for multi-parts.

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  • 2
    Not really. The way you state it can be confusing, and people might not know what you mean. The original question wanted to have data=foo sent to the server. The file called my-file.txt would contain only data=foo. Then the curl syntax would be curl -X POST -d @path/to/my-file.txt http://example.com. Your syntax is a bit non-standard and confusing.
    – Steve Storck
    Jul 17, 2021 at 2:13
  • Does not upload the file for me.
    – Yuki
    Aug 4, 2021 at 13:21

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