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Registry: HKEY_CURRENT_USER\Software\Microsoft\Command Processor

HKEY_CURRENT_USER\Software\Microsoft\Command Processor can be used to configure cmd.exe.

Autorun

If cmd.exe is started without the /D option, it executes the commands that are listed in the Autorun value first.
Autorun can also be specified in the respective key under HKEY_LOCAL_MACHINE.
Compare with HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run.
If the value contains the name of a batch file, extreme care needs to be taken that this batch file does not contain any command that starts another instance of cmd.exe, such as the for /f "usebackq" … construct. Otherwise, cmd.exe is instantiated recursively.
Should that happen nevertheless, the created cmd.exe processes might be killed with a taskkill /im cmd.exe /f.

CompletionChar / PathCompletionChar

The value specifies the ANSI(?) ASCII-value of the key to be pressed to complete a file name or directory name when editing the command line.
Setting it to 9 for both allows to complete file and directory with the tabulator.
The following PowerShell script sets the completion characters for both, files and directories, to the tabulator character:
$regPath = 'HKCU:\Software\Microsoft\Command Processor'

if (! (test-path $regPath) ) {
   write-output "$regPath does not exist, creating"
   $eatMe = new-item -path $regPath
}

$eatMe = new-itemProperty -path $regPath -name     CompletionChar -value 9 -propertyType DWord
$eatMe = new-itemProperty -path $regPath -name PathCompletionChar -value 9 -propertyType DWord
Github repository about-Windows-Registry, path: /HKEY_CURRENT_USER/Software/Microsoft/Command Processor/pathCompletion.ps1

EnableExtensions

If set to 1, command extensions are enabled by default.

See also

Compare with HKEY_CURRENT_USER\Console

Index