Add default value syntax for variable replacement

[Copilot]

Variable replacement currently substitutes empty strings when parameters are missing. This adds optional default value syntax: %%VARIABLENAME:DefaultValue%%.

Changes

Core implementation (Convert-SentinelARYamlToArm.ps1)

• Extended variable replacement regex to match %%VAR:default%% pattern in addition to %%VAR%%
• Applied negative lookahead (?!%%) to correctly parse default values containing % characters
• Replacement order: parameter values → default values → empty string

Syntax rules

• Variable names cannot contain : or % (prevents ambiguity)
• Default values can contain % (but not %% sequence)
• Parameters always override defaults

Example behavior

-- Input query
| where ErrorCount > %%Threshold:100%%
| where Code in (%%Codes:500%%)
| where Message contains "%%Filter%%"

-- With parameters: { Threshold: 50, Codes: [403, 404] }
| where ErrorCount > 50
| where Code in ("403","404")
| where Message contains ""

-- Without parameters
| where ErrorCount > 100
| where Code in (500)
| where Message contains ""

Testing

• Added test fixtures with mixed variable scenarios
• Tests cover: defaults only, parameters only, mixed, edge cases

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• www.powershellgallery.com
  • Triggering command: /usr/bin/pwsh pwsh -Command Set-PSRepository PSGallery -InstallationPolicy Trusted; Install-Module powershell-yaml, PSScriptAnalyzer, Pester -Force -Scope CurrentUser (dns block)
  • Triggering command: /usr/bin/pwsh pwsh -Command Install-Module powershell-yaml, PSScriptAnalyzer, Pester -Force -Scope CurrentUser -SkipPublisherCheck /home/REDACTED/work/SentinelARConverter/SentinelARConverter (dns block)
  • Triggering command: /usr/bin/pwsh pwsh -Command Register-PSRepository -Default -ErrorAction SilentlyContinue; Install-Module powershell-yaml, PSScriptAnalyzer, Pester -Force -Scope CurrentUser -SkipPublisherCheck (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Add option for variable default value</issue_title>
<issue_description>### Summary of the new feature / enhancement

When converted and no variable is provided a default fallback should be available

Proposed technical implementation details (optional)

Currently %%VARIABLENAME%% is replaced with the variable but with nothing if not available
A solution would be to have %%VARIABLENAME:DefaultValue%% as a optional text

%%VARIABLENAME%%` -> VARIABLENAME = "TEST" = "TEST"
%%VARIABLENAME%%` -> VARIABLENAME = null = ""
%%VARIABLENAME:10%%` -> VARIABLENAME = "20" = "20"
%%VARIABLENAME:10%%` -> VARIABLENAME = null = "10"
```</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes Add option for variable default value #50

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