Iterate JSON file and update values using shell script without JQ

Question

In shell script, I want to read the content from file swiftlint.json.

Iterate the array of dictionary with key issues. Read the value for key filePath and add /private in the beginning.

Here is the content of file

{
    "issues": [{
        "engineId": "SwiftLint",
        "primaryLocation": {
            "filePath": "\/RegistrationUtilities.swift",
            "message": "Function should have complexity 15 or less: currently complexity equals 18",
            "textRange": {
                "startLine": 29
            }
        },
        "ruleId": "cyclomatic_complexity",
        "severity": "MINOR",
        "type": "CODE_SMELL"
    }]
}