Overview

ARM Templates does not support local and relative paths. The only way to link to other files is to put them online.
This tool expects local and/or relative paths and merges your ARM templates into a one template.
A fuller narrative with example usage can be read on my blog here.

Install

install-module ARMLinker

PowerShell Usage

import-module ARMLinker
Convert-TemplateLinks -InputPath <path to main template> [-OutputPath <path to output file>]

If no output path is specified, the merged JSON is written to output.

Example input/output

azuredeploy.linked.json

{
    "$schema": "https//schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json#",
    "parameters": {},
    "resources": [
        {
            "templateLink": {
                "uri": "./aresource.json"
            }
        }
    ]
}

aresource.json

{
    "type": "Microsoft.Web/connections",
    "apiVersion": "2016-06-01",
    "properties": "..."
}

Running Convert-TemplateLinks azuredeploy.linked.json azuredeploy.json will output a merged version of the two in a file called azuredeploy.json:

{
    "$schema": "https//schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json#",
    "parameters": {},
    "resources": [
        {
            "type": "Microsoft.Web/connections",
            "apiVersion": "2016-06-01",
            "proper": "properties were probably here"
        }
    ]
}

If the JSON you want to link is at some deeper level in the linked JSON, you can specify a "jsonPath" as well:

azuredeploy.linked.json

{
    "$schema": "https//schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json#",
    "parameters": {},
    "resources": [
        {
            "templateLink": {
                "uri": "./aresource.json",
                "jsonPath": "special.path"
            }
        }
    ]
}

aresource.json

{
    "special": {
        "path": {
            "type": "Microsoft.Web/connections",
            "apiVersion": "2016-06-01",
            "properties": "..."
        }
    }
}

Incidentally...

This works with any JSON, but the main goal is for ARM templates.
Hence following the same convension as the supported "full online URL" feature.