File Redirection

File redirection intercepts calls to CreateFileW/A, GetFileAttributesW/A, FindFirstFileW/A, and the LoadLibrary family, replacing path arguments on the fly before the call reaches Windows. The game opens and reads the redirected file without any knowledge that its path was changed.

Why Use It

Common use cases:

• Portable save files — redirect a hard-coded save path (e.g. C:\Program Files\MyGame\saves\) to a per-user location (%USERPROFILE%\Saved Games\My Game\)
• Config file portability — redirect absolute paths baked into old games to locations inside the game directory
• Multi-user coexistence — different users can be redirected to different profile directories without modifying the game
• Registry-adjacent paths — some games write config to hard-coded paths under C:\Windows or C:\Program Files; redirect these to writable locations

Configuring Redirects

Redirects are defined as a list in .interposer/Config.yml under the FileRedirects key. Each entry has a Pattern (regex) and a Replacement:

FileRedirects:
  - Pattern: 'C:\\Games\\MyGame\\Saves\\(.+)'
    Replacement: '%USERPROFILE%\Saved Games\My Game\$1'

Backwards compatibility

The legacy key name Redirects is still accepted and behaves identically. It is read only when FileRedirects is not present, so prefer FileRedirects for new configs.

Use single-quoted strings for patterns

YAML single-quoted strings pass backslashes through literally. No extra escaping is needed when writing Windows paths as regex patterns. Double-quoted strings interpret YAML escape sequences and should be avoided here.

Rules are evaluated in order. The first matching rule wins. Subsequent rules are not checked once a match is found.

Pattern Syntax

Patterns are ECMAScript regular expressions, matched case-insensitively against the full file path.

In a single-quoted YAML string, each \\ represents one literal backslash character, which the regex engine then treats as a literal backslash (matching \ in a Windows path). To match a directory separator, write \\\\ in a double-quoted string or \\ in a single-quoted string.

You want to match	Single-quoted YAML	Regex sees
A literal backslash	'\\'	\\ (matches \)
C:\Games\MyGame\	'C:\\Games\\MyGame\\'	C:\\Games\\MyGame\\
Any characters	'(.+)'	(.+)
A literal dot	'\.'	\.

Patterns may also contain path tokens, which are substituted before the regex is compiled.

Tokens do not remove the need to double your own separators

The value a token expands to is regex-escaped for you, so never double the backslashes inside a token. Everything else in the pattern is still your regex, so a separator you write yourself still needs \\:

- Pattern: '%APPDATA%\\My Game\\(.+)'   # correct
- Pattern: '%APPDATA%\My Game\(.+)'         # wrong

In the second form \M is a regex escape, not a directory separator. It compiles without error and then matches nothing. Check the log at Level: Debug if a rule that looks right never fires.

Capture Groups

Use parentheses to capture parts of the matched path for use in the replacement:

- Pattern: 'C:\\Games\\MyGame\\Saves\\(.+)'
  Replacement: '%USERPROFILE%\Saved Games\My Game\$1'

For the path C:\Games\MyGame\Saves\profile.dat:

• $1 captures profile.dat
• The replacement expands to %USERPROFILE%\Saved Games\My Game\profile.dat (with %APPDATA% further expanded)

Up to nine capture groups ($1 through $9) are supported.

Replacement Syntax

Token	Meaning
$1 – $9	Replaced with the corresponding capture group from the pattern match.
%NAME%	Expanded as a path token after capture group substitution.

Token expansion happens after capture group substitution, so a capture group can itself contain a token reference if needed.

Path Tokens

%NAME% is resolved the same way in both Pattern and Replacement. A name is looked up in this order, and the first hit wins:

Source	Examples
Any Windows environment variable	%APPDATA%, %LOCALAPPDATA%, %USERPROFILE%, %PROGRAMDATA%, %TEMP%
A known folder Windows tracks but the environment does not	%SAVEDGAMES%, %DOCUMENTS%, %MYDOCUMENTS%, %MYGAMES%, %DESKTOP%, %PICTURES%, %MUSIC%, %VIDEOS%
The running executable's directory	%GAMEDIR%
The directory holding the Interposer DLL	%INTERPOSERDIR%

Because the environment is consulted first, a token that already exists as an environment variable keeps its existing meaning The known-folder table only covers names the environment leaves undefined.

Known folders are read from HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders, so a relocated Documents or Saved Games folder resolves to wherever it actually lives.

Unresolved tokens are left alone

A token that matches nothing is kept verbatim, delimiters included, rather than expanding to an empty string. The rule therefore fails to match instead of silently redirecting to a truncated path, and the name is reported once at startup:

2025-03-14 12:00:00  [FILEREDIRECT]  unresolved %MYGAMEDIR% in FileRedirects pattern: %MYGAMEDIR%\\saves\\(.+)

Examples

Redirect a save directory

FileRedirects:
  - Pattern: 'C:\\Games\\Quake\\id1\\save\\(.+)'
    Replacement: '%APPDATA%\Quake\save\$1'

Redirect an absolute config path to the game directory

%GAMEDIR% is the directory of the running executable, so this rule keeps working wherever the game is installed:

FileRedirects:
  - Pattern: 'C:\\Program Files.*\\MyGame\\config\.cfg'
    Replacement: '%GAMEDIR%\config.cfg'

Move an AppData save folder into Saved Games

Both sides use tokens, so nothing in the rule is tied to a particular user or drive:

FileRedirects:
  - Pattern: '%APPDATA%\\My The Lord of the Rings, The Rise of the Witch-king Files(.*)'
    Replacement: '%SAVEDGAMES%\EA Games\The Lord of the Rings - Battle for Middle-earth II - Rise of the Witch-king$1'

Note the (.*) with no separator in front of it: that matches the folder itself as well as everything under it, so the game's initial GetFileAttributes probe on the directory is redirected too. Writing \\(.+) instead would redirect only the files inside it.

Redirect multiple directories with one rule

This example redirects any file under C:\OldGame\data\ or C:\OldGame\mods\ to corresponding locations under %APPDATA%\OldGame\:

FileRedirects:
  - Pattern: 'C:\\OldGame\\(data|mods)\\(.+)'
    Replacement: '%APPDATA%\OldGame\$1\$2'

Multiple rules — first match wins

FileRedirects:
  - Pattern: 'C:\\Games\\MyGame\\Saves\\current\\(.+)'
    Replacement: '%USERPROFILE%\Saved Games\My Game\slot1\$1'
  - Pattern: 'C:\\Games\\MyGame\\Saves\\(.+)'
    Replacement: '%USERPROFILE%\Saved Games\My Game\$1'

The first rule redirects any path under current\ specifically; the second catches everything else under Saves\.

Verifying Redirects

Enable file logging and look for [FILE REDIRECT] entries:

2025-03-14 12:00:01  [FILE REDIRECT]  C:\Games\MyGame\Saves\profile.dat  ->  C:\Users\Pat\AppData\Roaming\MyGame\Saves\profile.dat

Diagnosing a rule that isn't firing

Set Logging.Level to Debug. Every file operation then reports whether a rule matched:

2025-03-14 12:00:01  [REDIRECT HIT]   C:\Games\MyGame\Saves\profile.dat  ->  rule #1  C:\\Games\\MyGame\\Saves\\(.+)
2025-03-14 12:00:01  [REDIRECT MISS]  C:\Games\MyGame\config.cfg  ->  2 rules, none matched

A [REDIRECT MISS] gives you the exact path the game asked for — copy it and test your pattern against it. A [REDIRECT HIT] names the 1-based rule number and its pattern, which is how you confirm that an earlier, broader rule isn't shadowing the one you intended (remember: first match wins).

When a pattern contains a path token, the hit line shows the compiled pattern first and the rule as you wrote it after it, so you can see exactly what the token expanded to:

2025-03-14 12:00:01  [REDIRECT HIT]   C:\Users\Pat\AppData\Roaming\My Game\save.dat  ->  rule #1  C:\\Users\\Pat\\AppData\\Roaming\\My Game\\(.+)  (as written: %APPDATA%\\My Game\\(.+))

If the miss says no rules configured, the FileRedirects block was empty or failed to parse — check for malformed regexes, which are skipped silently at load time.

For a stubborn pattern, Level: Trace adds a [REDIRECT RULE] line for every pattern that was evaluated and rejected against that path:

2025-03-14 12:00:01  [REDIRECT MISS]  C:\Games\MyGame\config.cfg  ->  2 rules, none matched
2025-03-14 12:00:01  [REDIRECT RULE]  C:\Games\MyGame\config.cfg  ->  C:\\Games\\MyGame\\Saves\\(.+)
2025-03-14 12:00:01  [REDIRECT RULE]  C:\Games\MyGame\config.cfg  ->  C:\\Games\\MyGame\\Demos\\(.+)

See Logging for the full list of diagnostic verbs.

Hooked Functions

File redirection applies to the following Windows API functions:

Function	Notes
CreateFileW / CreateFileA	Applies redirect before opening; ANSI variant converts to wide first.
GetFileAttributesW / GetFileAttributesA	Applies redirect before querying attributes.
FindFirstFileW / FindFirstFileA	Applies redirect before beginning enumeration.
LoadLibraryW / LoadLibraryA	Applies redirect before loading a DLL.
LoadLibraryExW / LoadLibraryExA	Applies redirect before loading a DLL with flags.