Starting applications on Windows

https://learn.microsoft.com/en-us/windows/win32/shell/app-registration

What can Windows invoke?

Windows can invoke files having an extension present in the PATHEXT environment variable, which might be similar to the following:

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PS> echo $env:PATHEXT
.COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC;.PY;.PYW

Also, Windows will try to infer the extension, if not specified, by parsing PATHEXT in order, one extension at a time, choosing the first existing file with that extension, only after choosing the first valid file location (see section below).

For example, if both x.exe and x.cmd exist in the current folder, x.exe is executed when running just x.

If x.cmd and x.exe exist both in the current directory, and in a directory in the system PATH, then the xs are executed in the following order:

• x.exe (current folder)
• x.cmd (current folder)
• c:\folder\in\path\x.exe
• c:\folder\in\path\x.cmd

Powershell peculiarity

Powershell runs files in the current directory only if the name is preceded by .\, or if using start instead of &:

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x                     # error
.\x                   # works
start -nonewwindow x  # works

For more information run: get-help about_Command_Precedence

Where does Windows look for apps?

When the ShellExecuteEx function is called with the name of an executable file in its lpFile parameter, there are several places where the function looks for the file. We recommend registering your application in the App Paths registry subkey. Doing so avoids the need for applications to modify the system PATH environment variable.

The file is sought in the following locations:

• The current working directory.
• The Windows directory only (no subdirectories are searched).
• The Windows\System32 directory.
• Directories listed in the PATH environment variable.
• Recommended: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths

Please note that the PATH environment variable contains multiple paths, separated by ;. If a path itself contains the semicolon, the path is enclosed in double quotes (eg. c:\windows;"c:\path;with;semicolon").

For example, if you have the Brave browser installed, you can open it with:

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start brave

but if you look for it via Get-Command (powershell) or where.exe, you will not find it:

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PS> Get-Command brave
Get-Command : The term 'brave' is not recognized as a name of a cmdlet, function, script file, or executable program.
Check the spelling of the name, or if a path was included, verify that the path is correct and try again.
At line:1 char:1
+ Get-Command brave
+ ~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo          : ObjectNotFound: (brave:String) [Get-Command], CommandNotFoundException
+ FullyQualifiedErrorId : CommandNotFoundException,Microsoft.PowerShell.Commands.GetCommandCommand

PS> where.exe brave
INFO: Could not find files for the given pattern(s).

This is because Brave registers itself in the system registry under the App Paths key:

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Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths\brave.exe]
@="C:\\Program Files\\BraveSoftware\\Brave-Browser\\Application\\brave.exe"
"Path"="C:\\Program Files\\BraveSoftware\\Brave-Browser\\Application"

Powershell peculiarity

Powershell doesn't treat the current working directory as first possible location of executables.

If x.exe exists both in the current directory and in a directory in the system PATH, when running x.exe, the latter takes precedence, for example.

For more information run: get-help about_Command_Precedence

Verbs, file associations, perceived types

TODO