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Using the Curl Utility to Call CM-Well

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The CM-Well API uses the REST protocol, which runs over HTTP. When running a REST GET command (one that retrieves or searches for infotons), you can simply paste the query into a browser address bar, press enter and see the query results in the browser window.

However, PUT, POST and DELETE commands (which update CM-Well's data) cannot be submitted in a browser. There are several ways that you can submit such calls:

  • From your own application, using a 3rd-party library that supports REST calls.
  • Using an online utility such as REST Test.
  • Using a client application such as Postman.
  • Using a command-line utility such as Curl.

Curl is a commonly-used utility for submitting REST requests. All the code examples that appear in CM-Well documentation use the Curl utility.

Here is an example of a call to CM-Well, which uploads a file infoton, using Curl:

curl -X POST <cm-well-host>/example/files/f1.png -H "X-CM-WELL-TYPE: FILE" -H "Content-Type: image/png" --data-binary @image.file.png

You can learn more about Curl from online resources such as Using curl to automate HTTP jobs.

Downloading Curl

You can download Curl from several sites, for example: Curl Releases and Downloads. Choose the package for your operating system (note that curl is already installed on Macs)

Running Curl on Windows vs. Unix

If you're running Curl in a command-line window, you should be aware of some syntactical differences between the Windows and Unix command-lines:

  • The line-continuation character in Unix is '\', while in Windows it's '^'. When entering multi-line commands, remember to use the correct character for your OS.
  • Unix supports single quotes as string delimiters ('string'), while Windows requires double-quotes ("string"). This can cause problems when using the JSON format, as cURL statements use single quotes to specify JSON data.

Note: You can avoid many syntax errors arising from these differences by providing the data for the Curl command in a file rather than on the command line. Many code examples in this documentation use files as input.

You can learn more at Using cURL in Windows.

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