REGDIFF - Version 5.0.0

regdiff is a command line tool to compare two registry files, export the registry, merge .REG files and much more. Version 5.0 is a complete rewrite in Go, providing cross-platform support for .REG file operations with native Windows registry access.

regdiff is freeware under the MIT license (free for any use including commercial).

Installation

go install github.com/gersonkurz/go-regdiff/cmd/regdiff@latest

Or build from source:

git clone https://github.com/gersonkurz/go-regdiff
cd go-regdiff
go build ./cmd/regdiff

Requirements

• Go 1.21 or higher (for building)
• Administrative rights for registry operations on Windows

Features

• Compare, diff and merge .REG files
• Compare, diff and merge the live Windows registry
• Export registry keys directly to .REG files
• Support for both ANSI (REGEDIT4) and Unicode (Windows Registry Editor Version 5.00) .REG files
• Variable substitution with $$VAR$$ syntax
• Parameter files (.INI format)
• Key aliasing for comparing renamed keys
• Cross-platform .REG file processing (Windows registry access requires Windows)

How to compare two .REG files

The most basic usage is specifying two filenames:

regdiff foo.reg bar.reg

How to export a registry key

You can export any registry key directly by specifying a registry path:

regdiff HKEY_LOCAL_MACHINE\SOFTWARE /MERGE:hklm_software.reg

Short hive names are also supported: HKLM, HKCU, HKCR, HKU, HKCC.

How to compare a registry key with a .REG file

Compare a live registry key against a .REG file:

regdiff HKEY_LOCAL_MACHINE\SOFTWARE hklm_software.reg

How to create a diff file

Use /DIFF to create a registry file containing only the differences between two sources. When comparing A and B:

• Keys/values in B but not in A are marked for addition
• Keys/values in A but not in B are marked for removal
• Changed values use data from B

regdiff old_settings.reg new_settings.reg /DIFF:changes.reg

How to create a merge file

Use /MERGE to create a registry file with merged content:

regdiff base.reg overlay.reg /MERGE:merged.reg

How to create a sorted .REG file

Specify a single input file with /MERGE to create a sorted, normalized output:

regdiff messy.reg /MERGE:sorted.reg

How to remove empty keys from output

Use /NO-EMPTY-KEYS to exclude keys that have no values:

regdiff input.reg /MERGE:output.reg /NO-EMPTY-KEYS

How to compare a .REG file against the live registry

Use /REGISTRY to compare a .REG file against the current registry state:

regdiff expected_settings.reg /REGISTRY

Difference between HKEY_* and /REGISTRY:

• HKEY_* reads all keys under the specified path from the registry
• /REGISTRY reads only the keys mentioned in the .REG file from the registry

How to compare renamed keys

Use /ALIAS to compare keys with different names:

regdiff old_version.reg new_version.reg /ALIAS:MyProduct.v1=MyProduct.v2

Multiple aliases can be specified by repeating the /ALIAS option.

Output format

The default output format is Unicode (Windows Registry Editor Version 5.00). Use /4 for the legacy ANSI format (REGEDIT4):

regdiff HKEY_CURRENT_USER\Software /4 /MERGE:output.reg

Writing to the registry

Use /WRITE to apply changes to the registry:

regdiff settings.reg /WRITE

When using /WRITE, the input file can contain:

• Comments starting with # or ; (always allowed with /WRITE, or use /COMMENTS for other operations)
• Variables using $$VARIABLE$$ syntax

Example with variables:

[HKEY_LOCAL_MACHINE\Software\MyCompany\Product\$$VERSION$$]
"InstallPath"="$$INSTALLDIR$$"
"Port"=dword:$$PORT$$

Variables can be defined via parameter files (/PARAMS):

INI parameter file format

; comments are allowed
# this style too

[SectionHeadersAreIgnored]
VERSION = 4.0
INSTALLDIR = C:\Program Files\MyApp
PORT = 8080

Security considerations

With /WRITE, default security attributes are used. The /ALLACCESS option grants full control to everyone - use with caution.

32-bit/64-bit registry views

On 64-bit Windows, use /32 or /64 to access specific registry views:

• /32 - Access 32-bit registry view (WOW6432Node)
• /64 - Access 64-bit registry view

Options reference

REGDIFF - Version 5.0.0
Freeware written by Gerson Kurz (http://p-nand-q.com) [64-bit]

Usage: regdiff [OPTIONS] FILE|HKEY_* {FILE|HKEY_*}

Options:
  /MERGE:<file>      Create merged output file
  /DIFF:<file>       Create diff output file
  /QUIET             Don't show diff on console
  /NO-EMPTY-KEYS     Don't create empty keys in output
  /4                 Use REGEDIT4 format (ANSI, non-unicode)
  /COMMENTS          Allow # and ; line comments in input
  /ALIAS:FOO=BAR     Alias key names for comparison (repeatable)
  /PARAMS:<file>     Parameter file for $$VAR$$ substitution (.ini)
  /REGISTRY          Compare input file against live registry
  /WRITE             Write result to registry (Windows only)
  /ALLACCESS         Grant all access when writing (use with /WRITE)
  /32                Use 32-bit registry view (default: 64-bit)
  /? or /HELP        Show this help

Examples:
  regdiff file1.reg file2.reg                    Compare two .REG files
  regdiff file1.reg file2.reg /DIFF:changes.reg  Create diff file
  regdiff HKEY_CURRENT_USER\Software /MERGE:out.reg  Export registry key
  regdiff settings.reg /REGISTRY                 Compare file with registry
  regdiff settings.reg /WRITE                    Apply .REG file to registry

Note: The /32 or /64 option shown depends on the process architecture. A 64-bit process shows /32 to access the 32-bit registry view, while a 32-bit process on 64-bit Windows shows /64 to access the 64-bit view.

Related Projects

• go-regis3 - The underlying Go library for .REG file parsing
• regdiff (C#) - The original .NET implementation (version 4.x)
• pnq - C++ header-only library including pnq::regis3

License

MIT License - see LICENSE file for details.