What is the reason for "X is not recognized as an internal or external command, operable program or batch file"?

Solution 1:

A) How does Windows command processor search for commands?

Windows command processor searches for a COMMAND to execute which

is not an internal command of cmd.exe and
is just specified with file name without file extension and without path

for a file matching the pattern command.* and having a file extension listed in local environment variable PATHEXT

first in current directory and
next in all directories of local environment variable PATH.

SORT and FIND and FINDSTR and ROBOCOPY and XCOPY and many more commands are not internal commands of cmd.exe. They are console applications installed with Windows located in directory %SystemRoot%\System32 having the file name sort.exe, find.exe, findstr.exe, robocopy.exe, xcopy.exe, ...

Such console applications available by default on Windows are called external commands to distinguish them better from console applications not installed with Windows operating system.

B) How is the environment variable PATH defined?

There are 3 types of PATH variables:

System PATH which is used for all accounts and stored in Windows registry under key:

 HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment

User PATH which is used only for current account and stored in Windows registry under key:
```
 HKEY_CURRENT_USER\Environment
```
Local PATH which is always a copy of the local PATH of parent process which started the current process.

Windows concatenates system and user PATH to local PATH for the Windows Explorer instance used as Windows desktop with the shortcuts on desktop screen and the Windows start menu as visible interface for the user.

On starting a new process the entire currently active environment variables table of running process is copied for the new process by Windows.

The parent process cannot modify the environment variables of any child process nor can a child process modify the environment variables of its parent process.

This means once a process like cmd.exe was started for execution of a batch file, the process has its own set of environment variables which only the process itself can modify. No other process can modify the environment variables of an already running process.

C) What does the error message mean?

The error message

'...' is not recognized as an internal or external command,
operable program or batch file.

always means that

the file name of a
- console application
- GUI application
- script (batch file, PowerShell script, Perl script, VBScript, JScript, ...)
was specified for execution most likely without file extension and without (complete) path to the executable/script file and
Windows failed to find a file matching the pattern FileName.* with a file extension listed in currently active environment variable PATHEXT in current directory or any other directory in currently active environment variable PATH.

D) What are the possible reasons for this error message?

Typical reasons are:

1. The file name of the file to execute was specified wrong due to a typing mistake.

Check character by character the name of the command/executable.

2. The current directory is different to the directory containing the file to execute.

Run echo Current directory is: %CD% on command line or add this line to the batch file above the command line which fails to see what the current directory is.

3. The executable or script to run is not installed at all.

Verify the existence of the executable to run. Some installation packages work only if other packages like Java, NPM, PHP, etc. were installed before.

4. The directory of the file to execute is not in PATH at all.

Open in Windows Control Panel the System settings window, click on Advanced system settings on left side, click on button Environment Variables and look in both lists for Path and their values. By default Path exists only in list of System variables.

5. A running process/application was not restarted after modification of system or user PATH .

A modification of system PATH or user PATH with command setx or via Control Panel – System – Advanced system settings was made by the user or an installer, but an already running process/application like an opened command prompt or PowerShell window was not closed/exited and opened/restarted after PATH modification. This is necessary as described in detail in chapter F) below.

6. An executable in %SystemRoot%\System32 is not found on 64-bit Windows.

There is the directory %SystemRoot%\System32 with 64-bit executables and %SystemRoot%\SysWOW64 with 32-bit executables on 64-bit Windows. Most executables exist in both directories. But there are some executables existing only in System32 and a few only in SysWOW64.

The system PATH contains by default as first folder path %SystemRoot%\System32. But which one of the two Windows system folders is searched for the executable specified without path or with the path %SystemRoot%\System32 depends on the execution environment. An application or script executed in 64-bit environment is really accessing %SystemRoot%\System32 while an application or script executed in 32-bit environment is redirected by the Windows file system redirector to the directory %SystemRoot%\SysWOW64.

An application or script running in 32-bit environment which wants to run a 64-bit executable in %SystemRoot%\System32 has to use full qualified file name of the executable with file path %SystemRoot%\Sysnative.

Note: %SystemRoot%\Sysnative is neither a directory nor any type of link. It is something very special existing only for x86 applications. It does not exist for amd64 applications. The condition if exist %SystemRoot%\Sysnative in a batch file is always false in both environments, but if exist %SystemRoot%\Sysnative\cmd.exe is true in 32-bit execution environment and false in 64-bit environment and also on 32-bit Windows. This condition can be used in batch scripts to find out if the batch file is processed by 32-bit cmd.exe in %SystemRoot%\SysWOW64 on 64-bit Windows which can be important to know depending on the task.

See also the Microsoft documentations WOW64 Implementation Details and Registry Keys Affected by WOW64.

7. PATH contains a reference to a not (yet) defined environment variable.

It is possible to specify in PATH a folder path using a reference to value of another environment variable like SystemRoot. It is important that this environment variable is also defined in same set of environment variables or a set of environment variables processed first by Windows.

For example if %JAVA_HOME%\bin is added to system PATH environment variable, there must be defined also a system environment variable JAVA_HOME with the base folder path to Java program files. It is not enough to have defined a user environment variable JAVA_HOME or define the environment variable JAVA_HOME later in the local environment of a batch file.

%JAVA_HOME%\bin added to user PATH is expanded by Windows to a full qualified folder path if the environment variable JAVA_HOME is defined either as system or as user environment variable, but not on JAVA_HOME defined later in the local environment of a Windows command process.

Such a mistake can be seen easily by opening a new command prompt window after making a modification on system or user PATH from Windows start menu and running set path. The output PATH should not contain anymore any %Variable% environment variable value reference.

8. The LOCAL variable PATH was modified before on command line or in batch file.

Run set path on command line or add this command to the batch file above the command line which fails to see the current values of the environment variables PATH and PATHEXT.

The last reason is responsible for external command SORT not being found on execution of the batch file which contains somewhere above set path=....

E) How to avoid this error message?

Best is coding a batch file for being independent on PATH and PATHEXT and the order of directories in PATH which means here using the command line:

FOR /f "delims=" %%d in ('dir /s /b /ad ^| %SystemRoot%\System32\sort.exe /r') do rd "%%d"

Any external command of which executable is stored in %SystemRoot%\System32 should be specified in a batch file with this path and with file extension .exe. Then Windows command interpreter does not need to search for a file using local PATH and PATHEXT and the batch file works always (as long as environment variable SystemRoot is not also modified in the batch file which I have never seen).

F) When is a system or user PATH change applied to processes?

When a user opens a command prompt window via Windows start menu or from within a Windows Explorer window, the user starts cmd.exe with implicit using option /K to keep the console window open after finishing a command which is good for debugging a batch file.

When a batch file is doubled clicked in Windows Explorer, the user starts cmd.exe for processing the batch file with implicit using option /C to close the console window after finishing batch processing which is not good for debugging a batch file as error messages cannot be seen in this case.

In both cases Windows creates a copy of the environment variables of the application starting cmd.exe which is usually Windows Explorer. Therefore the started command process has a local PATH of which value is the same as the parent process had on starting cmd.exe.

Example:

Open a command prompt window, run title Process1 and run set path.
Output is PATH and PATHEXT as currently defined for current user account in the console window having now the window title Process1.
Run set PATH=%SystemRoot%\System32 and next once again set path.
Output is again PATH and PATHEXT, but with PATH containing only one directory now.
Run start "Process2" and run in new console window with window title Process2 the command set path.
Output is PATH and PATHEXT with same values as before in Process1.
This demonstrates that on starting a new process the current environment variables of running process are copied and not what Windows itself has currently stored in Windows registry.
Run in Process2 the command set PATH= and next set path.
Output is only PATHEXT because local PATH does not exist anymore for Process2.
This demonstrates that every process can modify its environment variables including complete deletion.
Switch to Process1 window, run the command set PATH=%PATH%;%SystemRoot% and next set path.
Output is PATH with two directories and PATHEXT.
Run the command start "Process3" and in opened window with title Process3 the command set path.
Output is PATH with two directories as defined also for Process1 and PATHEXT.
Run in Process3 the command set PATH=%SystemRoot%\System32.

There are 3 command processes running with following values for local PATH when %SystemRoot% expands to C:\Windows:

Process1: PATH=C:\Windows\System32;C:\Windows
Process2: PATH does not exist at all.
Process3: PATH=C:\Windows\System32

So what happens now on opening Control Panel – System – Advanced System Settings – Environment Variables and adding to list of User variables the new environment variable PATH with value C:\Temp, or in case of there is already a user PATH environment variable, edit PATH and append ;C:\Temp to the value?

Well, as long as the dialog window with title Environment Variables showing the two lists is opened, nothing happens on modifying the variables, until button OK is clicked to take over all changes into Windows registry and close the window.

Let's go back to the three running command processes and run in Process1, Process2 and Process3 the command set path. It can be seen:

Process1: PATH=C:\Windows\System32;C:\Windows
Process2: PATH does not exist at all.
Process3: PATH=C:\Windows\System32

Nothing changed on already running processes.

No process can modify the environment variables of a different running process!

Open from Windows start menu one more command prompt window and run in fourth command process the command set path. It can be seen that local PATH of fourth command process has appended the directory C:\Temp now.

Then close all four command processes and delete the added user PATH respectively remove ;C:\Temp from user PATH if having appended this directory path before.

How is this possible if no process can modify the environment variables of an already running process?

How was the environment variables list of Windows Explorer instance running as Windows desktop modified on closing Environment Variables window with button OK?

The answer on those two questions was given by eryksun in his comment.

After writing the modifications on system and user variables into registry on clicking button OK of Environment Variables window, Windows sends the WM_SETTINGCHANGE message to all top-level windows to inform the running applications about changed system parameters.

It is up to the application if this event message is handled at all and how. Windows Explorer running as Windows desktop reads the environment variables from registry and updates its environment variables list accordingly. Other applications like Total Commander handle this message also and update their lists of environment variables too. But cmd.exe does not do that fortunately as this would be really problematic.

Is there any possibility to modify a system or user variable with notification via WM_SETTINGCHANGE from within a command prompt window or batch file?

It is possible to modify the registry value of an environment variable using reg add command. But this does not result in sending WM_SETTINGCHANGE message to all top-level windows. Such changes done with reg add or with regedit require a restart of Windows (or at least a log off and log on of current user) to be taken into account at all.

But there is also the command setx which is designed for modifying a system or user variable and which also sends the WM_SETTINGCHANGE message to all top-level windows after registry was updated according to specified arguments. Run setx /? in a command prompt window for details. But please take into account that setx does not modify the local environment variable of running command process. This must be done with using command set used in addition to setx.

G) How is environment variable PATHEXT handled by Windows?

The environment variable PATHEXT with the list of file extensions is handled by Windows different in comparison to environment variable PATH.

System PATHEXT and user PATHEXT are NOT concatenated to local PATHEXT.

A user PATHEXT replaces the system PATHEXT for all processes running under environment of the account having defined a user PATHEXT.

There is defined only a system PATHEXT environment variable by default.

H) Is it possible to disable file search in current directory?

Windows command processor searches by default in current directory if file name of a script file or executable is specified on command line or in a batch file without any path which means without a backslash \ (or a forward slash / thanks to auto-correction) in argument string.

But on Windows Vista and later Windows client versions and on Windows Server 2003 and later Windows server versions it is indeed possible to disable searching for a script/executable in current directory specified without at least relative path .\ by defining the environment variable NoDefaultCurrentDirectoryInExePath with any value as written by eryksun in his comment below and explained by Microsoft's documentation about function NeedCurrentDirectoryForExePathA.

See Removing the current working directory from the path for more details on usage of this environment variable.

Solution 2:

Most probably, you messed around with the PATH variable. Perhaps you are overwriting it somewhere else in your script. Since sort is an external command, opposed to all the others in your command line like for, dir, rd, which are cmd-internal commands, the PATH variable is needed to find the command. If PATH is not defined, external commands are searched in the current working directory only. There is also a PATHEXT variable that is needed to define standard file extensions for executables, like .com, .exe. So when sort appears in command prompt or in a batch file, the system searches the current working directory and all directories specified by the PATH variable for a file with the base name sort and one of the extensions specified by PATHEXT. The command sort is actually called sort.exe and is usually located in C:\Windows\System32.