JavaScript Requires Chilkat v11.5.0+

curl with Variable Substitution in a JSON Request Body

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This example shows how to use variables inside a JSON request body using the {{variable_name}} syntax. When the HTTP request’s Content-Type indicates JSON, Chilkat automatically applies proper JSON escaping to each substituted value, ensuring the resulting JSON remains valid. JavaScript

var success = false;

//  Variable names are enclosed between {{ and }}
//  Important: The variable {{var_name}} should be placed inside the quotes.

//  This is correct:
//  curl -X POST https://api.example.com/messages \
//    -H "Content-Type: application/json" \
//    -d '{"text":"{{message}}"}'

//  This is incorrect:
//    -d '{"text":{{message}}}'

var sbCurl = new CkStringBuilder();
sbCurl.AppendLn("curl -X POST https://api.example.com/messages \\");
sbCurl.AppendLn("  -H \"Content-Type: application/json\" \\");
sbCurl.AppendLn("  -d '{\"text\":\"{{message}}\"}'");

var curl = new CkHttpCurl();

//  In this example, the value we'll provide for the "message" variable
//  will contain chars that require JSON escaping.
curl.SetVar("message","He said \"Hello, world!\"");

//  To demonstrate how the variables are replaced, this example does not execute the curl command. 
//  Instead, it generates the raw HTTP request that would be sent if the curl command were run.
var sbRawRequest = new CkStringBuilder();
success = curl.ToRawRequest(sbCurl.GetAsString(),sbRawRequest);
if (success == false) {
    console.log(curl.LastErrorText);
    return;
}

console.log(sbRawRequest.GetAsString());

//  The output is shown below.
//  Notice that the quote chars around "Hello World!" are properly JSON escaped.

//  POST /messages HTTP/1.1
//  Host: api.example.com
//  Content-Type: application/json
//  Content-Length: 36
//  
//  {"text":"He said \"Hello, world!\""}