(PowerShell) 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.

Note: This example requires Chilkat v11.5.0 or greater.

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Add-Type -Path "C:\chilkat\ChilkatDotNet47-x64\ChilkatDotNet47.dll"

$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}}}'

$sbCurl = New-Object Chilkat.StringBuilder
$sbCurl.AppendLn("curl -X POST https://api.example.com/messages \`")
$sbCurl.AppendLn("  -H `"Content-Type: application/json`" \`")
$sbCurl.AppendLn("  -d '{`"text`":`"{{message}}`"}'")

$curl = New-Object Chilkat.HttpCurl

# 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.
$sbRawRequest = New-Object Chilkat.StringBuilder
$success = $curl.ToRawRequest($sbCurl.GetAsString(),$sbRawRequest)
if ($success -eq $false) {
    $($curl.LastErrorText)
    exit
}

$($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!\""}