I recently needed to compare post data from cUrl and webMethods 9.9. The cUrl request worked like a charm but the same request from the pub.client.http service failed to be recognized by the consumer. I then got a tip from a colleague to use the netcat program to catch the output from both programs and compare the results. Here is how I did:

Start a listener on an non-privileged port eg. 8000

nc -l 8000

With this running in one console window we switch to another and run a curl command eg.

curl -F attachment=@file.csv http://localhost:8000

The file.csv in this example is a MIME message

The message is now captured and written to the console like this:

POST / HTTP/1.1
Host: localhost:8000
User-Agent: curl/7.54.0
Accept: */*
Content-Length: 382
Expect: 100-continue
Content-Type: multipart/form-data; boundary=--10e698fa110003d5

----10e698fa110003d5
Content-Disposition: form-data; name="attachment"; filename="file.csv"
Content-Type: application/octet-stream

HELLO WORLD

----10e698fa110003d5--

TIP 1:
Start nc like this:

 
nc -l localhost 8000 &

Now run curl like this:

 
curl --proxy localhost:8000 --silent --max-time 1 http://blog.niklasottosson.com

And you will catch one and one only request

TIP 2:
Start nc like this:

nc -l loclahost 8000 > request.txt 

And you will catch the request in a file called request.txt

Tested on OSX 10.13.6 and cUrl 7.54.0