In previous articles, we used a REST client plug-in to Firefox or Chrome to exercise the HPE Composable Infrastructure API. This is nice, for discovery and understanding of the API, but the next step toward a software-defined infrastructure is to be able to automate those actions, in a script. One possible approach to writing automation scripts using a REST API such as the HPE Composable Infrastructure API, is to use a tool like curl, and open source command line tool able to exchange data with a web application or API using an URL syntax. cURL (Command-line URL) is available for just about any device and any operating system, and actually used by millions of users. More on cURL from https://curl.haxx.se.

cURL syntax 101

Let us remember how we described a REST call in our first article:

> Verb protocol://server-end-point/URI

With some examples such as:

• POST https://oneviewsrv.cilab.net/rest/login-sessions

• GET https://oneviewsrv.cilab.net/rest/alerts

So how do these calls translate in cURL?

We can call cURL with no option, and see the syntax: **curl [options...]

There are many available options but let us focus on the most important ones:

So let us try!

On a Linux machine with Internet access, type the following command, which will retrieve the version of the API.

curl -i -k -H "accept: application/json" \\
-X GET https://213.30.139.22:37441/rest/version

Parsing JSON

We can see in the last line of the above example that the response is provided in JSON (we asked for it with our accept HTTP header). So in order to write powerful scripts, we will need a mechanism to parse the JSON responses to extract the fields that we need. We have found this convenient open source tool called jq (command line JSON processor) available from http://stedolan.github.io/jq/download/linux64/jq

Once installed you can use it like this:

curl -k -H "accept: application/json" \\
-X GET https://213.30.139.22:37441/rest/version | jq -r "."

This will just pretty print the JSON response, but you can also extract field, for example to retrieve the currentVersion.

curl -k -H "accept: application/json" \\
-X GET https://213.30.139.22:37441/rest/version | jq -r ".currentVersion"

So let us pretend would like to capture the currentVersion in a variable within a shell script, we could do the following:

#Retrieve API version

currentVersion=$(curl -k -H "accept: application/json" -X GET
https://213.30.139.22:37441/rest/version | jq -r ".currentVersion")

echo $currentVersion

Getting a Session token

Let us now apply this technique to login to our HPE OneView Appliance and start managing our HPE Composable Infrastructure. As we have already seen in previous articles, we need to send a POST to the /rest/login-sessions API.

curl -k -H "accept: application/json" -H "content-type:
application/json" \\
-d '{"userName":"Administrator","password":"password"}' \\
-X POST https://213.30.139.22:37441/rest/login-sessions | jq -r "."

We can then, extract the sessionID in a variable using the following syntax:

sessionID=$(curl -k -H "accept: application/json" -H "content-type:
application/json" \\
-d '{"userName":"Administrator","password":"password"}' \\
-X POST https://213.30.139.22:37441/rest/login-sessions | jq -r ".sessionID")

echo $sessionID

Putting it all together

We have now retrieved the API Version (currentVersion) and a login session (sessionID), we are now ready to explore the full HPE Composable Infrastructure API with a simple shell script. For example, let us enumerate the models of the servers managed in this environment

curl -k -H "accept: application/json" -H "content-type:
application/json" \\
-H "x-api-version: $currentVersion" -H "auth: $sessionID" \\
-X GET https://213.30.139.22:37441/rest/server-hardware \\
| jq -r ".members\[\].model"

cURL on Linux and Windows

But what about Windows? Some of you might ask. The good news is that everything we have just shown here, can be done on Windows. If you use cygwin, the cURL package is part of the default distribution and jq can be easily compiled from sources located at https://stedolan.github.io/jq/download/

Another option is to install jq and cURL for Window, and in that case, you will have to perform a few syntax changes to the examples we showed above.

• cURL if available from: http://winampplugins.co.uk/curl/curl_7_48_0_openssl_nghttp2_x64.7z

• jq is available from: https://github.com/stedolan/jq/releases/download/jq-1.5/jq-win64.exe

Once curl and jq are installed and in the default path, we can then execute the following command to retrieve a sessionID:

curl -k -H "accept: application/json" -H "content-type:
application/json" -X POST
https://213.30.139.22:37441/rest/login-sessions -d
"{\\"userName\\":\\"Administrator\\",\\"password\\":\\"password\\"}" |
jq -r ".sessionID"

However, if you really need to store it into a variable in Windows command interpreter, things get a little more complicated:

for /f "delims=" %a in ('curl -k -H "accept: application/json" -H "content-type: application/json" -X POST https://213.30.139.22:37441/rest/login-sessions -d "{\"userName\":\"Administrator\",\"password\":\"password\"}" ^| jq -r ".sessionID"') do @set sessionID=%a

echo %sessionID%

And the last good news is…

So I asked early on, how do these calls translate in cURL? Here is the last piece of good news: POSTman can help you with that. Imagine you have been experimenting with a GET in POSTman, and you would like to run the same GET from cURL in a script

You can use the Generate Code button in the upper right corner and select cURL from the drop down to get the right string ready to paste in your own script.

What is next?

Scripting with cURL might solve a number of use cases, and is somewhat portable across Linux and Windows, but it is not the most convenient and readable scripting language. In the next articles, we will cover how to script against the HPE Composable Infrastructure API using Microsoft PowerShell and Python.