I am tweaking the PATH on several W2k3 servers in PowerShell to convert certain paths with blank spaces to their 8.3 equivalents. After several regex transformations, I run the following two commands:
# Set the path for this process
$env:PATH = $path
# Set the path for the Machine
[System.Environment]::SetEnvironmentVariable('PATH', $path,[System.EnvironmentVariableTarget]::Machine)
After running them, the path is changed in ways I didn't intend. %SystemRoot% is uniformly expanded to C:\Windows. I can't see where this signals the apocalypse, but I'd rather keep the %SystemRoot%, so I fiddled until I got %SystemRoot% to appear in the path again, but when I do the path no longer expands and no longer works. Echoing the path at the CLI returns an unexpanded string (this is wrong) and commands in the SystemRoot can no longer be found.
If I then add a null entry to the Path ";;", without altering any other text in the PATH, it begins to work correctly.
So my question is how to alter the path programmatically using PowerShell so as not to muck up variable expansion within the path?
As far as I can tell, you can't do this with the [Environment]::SetEnvironmentVariable() method and you can't do this with the Registry provider. However you can access the system Path env var in the registry using the Microsoft.Win32.RegistryKey class like so:
C:\PS> $key = [Microsoft.Win32.Registry]::LocalMachine.OpenSubKey('SYSTEM\CurrentControlSet\Control\Session Manager\Environment', $true)
C:\PS> $path = $key.GetValue('Path',$null,'DoNotExpandEnvironmentNames')
C:\PS> $path
...;%systemroot%\System32\WindowsPowerShell\v1.0\
C:\PS> $key.SetValue('Path', $path + ';%Windir%\Symbols', 'ExpandString')
C:\PS> $key.Dispose()
This will allow you to save the updated PATH and preserve the variables that appear in the Path value.
Related
I have downloaded exercism CLI and added it to the PATH. I can access it using the exercism command through cmd but on Windows Powershell, It is giving me the error that It doesn't recognize the command.
Does Powershell uses some different environment variable or am I missing something.
Generally speaking:
PowerShell respects the entries in the Path environment variable the same way that cmd does.
These shells only differ with respect to executing executables located in the current directory (assuming it isn't listed in Path): cmd.exe allows execution by name only (e.g., exercism), whereas PowerShell, as a security feature, requires use of a path to explicitly signal the intent (e.g., .\exercism)
After having modified the persistent Path definitions in the registry, a new shell session has to be started via the Windows GUI shell (Start Menu, taskbar) to see the changes. When in doubt, log off and back on again, or reboot.
Your Path value is misconfigured:
There should be no references to environment variables such as %EXERCISM% in your in-session Path value - neither cmd.exe nor PowerShell will recognize such references in this context; they interpret the entries verbatim (in contexts where variable references are recognized, only cmd.exe would recognize the syntax form %EXERCISM%; the PowerShell equivalent would be $env:EXERCISM)
In the registry, where the persistent environment-variable definitions are stored, you can base Path entries on references to other environment variables (e.g, %SystemRoot%\System32). The system itself ensures that (shell) processes see only the expanded forms of these variables. That is, what a process sees as the Path variable value is normally a ; separated list of verbatim paths (and is a concatenation of the machine-level and the user-level values).
This mechanism relies on the relevant registry Path values - in keys HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Session Manager\Environment (machine-level) and HKEY_CURRENT_USER\Environment (user-level) - to be defined as REG_EXPAND_SZ, which they are by default.
Your screenshot suggests that (at least) your user-level key has been converted to a static string value, REG_SZ, which prevents the necessary expansion of environment-variable references.
This quiet corruption can easily happen if you use tools such as setx.exe or even the .NET [Environment]::SetEnvironmentVariable() API to update the persistent Path values - see this answer.
The proper way to update the persistent Path values is via direct registry access (which is unfortunate, given the complexity) - see this answer.
Fix:
Re-convert your persistent user-level Path definition to value type REG_EXPAND_SZ, as follows (works analogously for the machine-level definition, in which case elevation (run as admin) is required):
$regPath = 'registry::HKEY_CURRENT_USER\Environment'
Set-ItemProperty -Type ExpandString -LiteralPath $regPath Path (Get-ItemPropertyValue -LiteralPath $regPath Path)
Something looks broken by something installed. These reg entries should be reg_expand_sz. You should not see %VARS% when viewing the path from the commandline.
get-item hkcu:\environment | % GetValueKind path
ExpandString
get-item HKLM:\SYSTEM\CurrentControlSet\Control\Session` Manager\Environment |
% GetValueKind path
ExpandString
I have a one-line snippet that works perfectly in the command line, but fails and throws up errors when I run it as part of a batch script.
The below commands behaves as expected, deleting all empty subfolders in the folder.
for /f "delims=" %d in ('dir /s /b /ad ^| sort /r') do rd "%d"
However, when put in a batch file like so...
FOR /f "delims=" %%d in ('dir /s /b /ad ^| sort /r') do rd "%%d"
...it throws the standard error:
Sort is not recognised as an internal or external command
I've been experimenting for the last hour or so with and without escaping the pipe, changing the order of the options, looking up the documentation of both dir and sort, etc., but I've still not been able to figure out what's going on here. The rest of the batch file, which is only a few lines, works fine, and this is the only line in it that fails.
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 three 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 the desktop screen and the Windows start menu and the Windows taskbar as visible interface for the user called Windows shell from which users usually start programs.
The entire currently active environment variables list of running process is copied for the new process by Windows on starting a new process. The Windows kernel library function CreateProcess does this environment variables list copy from the memory of the current process to the memory of the new process on function parameter lpEnvironment (long pointer to environment) being a null pointer. One of the CreateProcess functions is always used on Windows on starting an executable from another executable.
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 and Security – System – Advanced system settings - Environment Variables 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 with a processor supporting also the x86 instruction set. 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 the fully 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.
That reason is responsible for external command SORT not being found on execution of the batch file which contains somewhere above set path=....
9. LOCAL variable PATH is too long.
The local variable PATH of cmd.exe is too long. The Windows Command Processor fails to find any executable/script in the folder paths of local Path if the string value is longer than 8191 characters.
Please see my second answer here for more details regarding to length limitations of PATH.
Thanks goes to Albert Mosiałek for informing me about this cause of a not recognized program or script.
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.
I) How to modify system or user PATH?
The system and user PATH environment variables are modified by a user best using the Windows GUI dialog window Environment Variables. This dialog window can be opened as follows:
Click on the Windows Start menu button.
Type on keyboard environment variables.
There are offered by Windows the two items:
Edit the system environment variables
Edit environment variables for your account
Click on one of the two items to open the Environment Variables window.
There can be also opened the Windows Control Panel. There must be next clicked on System and Security with Category selected for display option View by. Next must be clicked System. There must be clicked on left side Advanced system settings and next on the button Environment Variables...
The System window can be opened also by pressing the key combination Windows logo key + Pause if the keyboard has the key Pause at all or at least in combination with the key Fn. See also the Microsoft documentation page Keyboard shortcuts in Windows.
The further user actions are self-explaining for editing either user Path in upper list on existing at all or system Path in lower list.
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.
In my case, I was so sure that I didn't mess with PATH. It was that I wasn't aware that path and PATH are the same. CMD is case insensitive.
This answer contains additional information to my first answer here regarding to length limitations of PATH.
There are not good coded executables/scripts which modify system or user PATH without checking first if the folder path to add is not already in string value of one of the two PATH environment variables as reported by Albert Mosiałek in a comment. Multiple executions of such a program results in local PATH string value of cmd.exe becomes longer and longer until reaching the PATH length limitations.
The maximum length of local PATH string value of cmd.exe depends on version of Windows and multiple string length limitations.
Length limitations of PATH on Windows Vista and Windows 7
Length limitations of system PATH
The system PATH as stored in Windows registry is truncated to its maximum length of 4095 characters before expanding all the environment variable references. The truncated string assigned to local PATH of cmd.exe can be also shorter than 4095 characters on system PATH contains environment variable references like %SystemRoot% (12 characters) expanding to C:\Windows (10 characters) and no user PATH is stored in Windows registry.
The system PATH is truncated to its maximum length of 4095 characters after expansion of the environment variable references. The truncated string assigned to local PATH of cmd.exe can be longer than the string value stored in Windows registry if environment variable references expand to strings which are longer than the environment variable reference strings.
In worst case the system PATH is truncated twice to a maximum length of 4095 characters, the first time before and the second time after expansion of the environment variable references.
Length limitations of user PATH
The user PATH is ignored completely independent on length of system PATH if the string value stored in Windows registry is longer than 4095 characters.
The user PATH is appended with an additional semicolon in expanded form to local PATH of cmd.exe on being in Windows registry not longer than 4095 characters even if the user PATH is in expanded form longer than 4095 characters because of environment variable references like %APPDATA%, %LOCALAPPDATA% or %USERPROFILE%.
The local PATH of cmd.exe can reach the maximum length of 8191 characters in worst case with a very long and perhaps already once or twice truncated system PATH and a user PATH not longer than 4095 characters in Windows registry, but longer than 4095 characters in expanded form.
The Windows Command Processor cmd.exe stops finding any executable on local PATH becomes too long, for example if the system PATH of 4095 characters in registry expands to a string with 4087 characters and is concatenated with a semicolon and a user Path stored in Windows registry with 4074 characters, but is expanded to a string value of length 4104 characters, resulting in a local Path with a total length of 8192 characters. There is not even found anymore any executable in %SystemRoot%\System32 on local PATH string value has a length of 8192 characters although the execution of set path outputs the local PATH with first directory path C:\Windows\System32.
There is the Command prompt (Cmd. exe) command-line string limitation which means that the environment variable name PATH plus equal sign = plus the variable string value plus the string terminating null byte must fit into a character array of 8192 characters. The string value of the local environment variable PATH as output on running set path in a command prompt window cannot be longer than 8186 characters for that reason although in memory the string value of local Path can be up to 8191 characters.
The internal command SET of cmd.exe does not output anymore a line-feed on running set path in a command prompt window if the local PATH has a string value of 8186 or more characters. In the console window is displayed for that reason in this case the environment variable PATHEXT with the equal sign and its string value appended to end of the string value of the environment variable PATH.
Length limitations of Control Panel windows for editing environment variables
A user or system PATH or any other in Windows registry persistent stored environment variable with a string value longer than 4094 characters is not displayed in the Environment Variables dialog window. For a user it looks like the environment variable does not exist which has a string value with more than 4094 characters although the environment variable is stored in registry and is perhaps even defined in local environment of running processes. The other user and system variables are still displayed in the Environment Variables window.
The Edit User Variable and Edit System Variable dialog windows display a Variable value with up to 4094 characters. A user can delete characters from such a long string value and save the shortened string value. But a user cannot append characters or replace existing characters on string value of the environment variable is longer than 2047 characters. A user can edit for that reason a user or system environment variable PATH with a string value longer than 2047 characters only for removal of a directory path using the Environment Variables window of Control Panel, but not for changing characters of an existing directory path or adding one more directory path to the environment variable string which is longer than 2047 characters.
Recommendations for PATH lengths
The system as well as the user PATH as stored in Windows registry and in their expanded form should be never longer than 4094 characters on Windows Vista and Windows 7 and are best both shorter than 2048 characters to be editable in the Control Panel windows.
Length limitations of PATH on Windows XP
Length limitations of system PATH
The system PATH as stored in Windows registry is truncated to its maximum length of 2047 characters before expanding all the environment variable references. The truncated string assigned to local PATH of cmd.exe can be also shorter than 2047 characters on system PATH contains environment variable references like %SystemRoot% (12 characters) expanding to C:\Windows (10 characters) and no user PATH is stored in Windows registry.
The system PATH is truncated to its maximum length of 2047 characters after expansion of the environment variable references. The truncated string assigned to local PATH of cmd.exe can be longer than the string value stored in Windows registry if environment variable references expand to strings which are longer than the environment variable reference strings.
In worst case the system PATH is truncated twice to a maximum length of 2047 characters, the first time before and the second time after expansion of the environment variable references.
Length limitations of user PATH
The user PATH is ignored completely if the expanded system PATH concatenated with the expanded user PATH with an additionally inserted semicolon results in a string value longer than 2047 characters. The maximum length of the user PATH on Windows XP depends for that reason on current length of expanded system PATH.
Length limitations of Control Panel windows for editing environment variables
A user or system PATH or any other in Windows registry persistent stored environment variable with a string value longer than 4095 characters is not displayed in the Environment Variables dialog window. For a user it looks like the environment variable does not exist which has a string value of more than 4095 characters although the environment variable is stored in registry and is perhaps even defined truncated in the local environment of running processes. The other user and system variables are still displayed in the Environment Variables window.
The Edit User Variable and Edit System Variable dialog windows display a Variable value with up to 2047 characters. A user can edit an even longer string value and save the string value, but the string value is always truncated to a maximum length of 2047 characters as displayed in edit field of the window. A user cannot append characters or replace existing characters on string value of the environment variable is longer than 2047 characters.
Recommendations for PATH lengths
The system PATH as stored in Windows registry and in its expanded form should be never longer than 2047 characters on Windows XP.
The user PATH in its expanded form should be short enough to be not ignored on concatenating it with the system PATH.
I have a one-line snippet that works perfectly in the command line, but fails and throws up errors when I run it as part of a batch script.
The below commands behaves as expected, deleting all empty subfolders in the folder.
for /f "delims=" %d in ('dir /s /b /ad ^| sort /r') do rd "%d"
However, when put in a batch file like so...
FOR /f "delims=" %%d in ('dir /s /b /ad ^| sort /r') do rd "%%d"
...it throws the standard error:
Sort is not recognised as an internal or external command
I've been experimenting for the last hour or so with and without escaping the pipe, changing the order of the options, looking up the documentation of both dir and sort, etc., but I've still not been able to figure out what's going on here. The rest of the batch file, which is only a few lines, works fine, and this is the only line in it that fails.
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 three 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 the desktop screen and the Windows start menu and the Windows taskbar as visible interface for the user called Windows shell from which users usually start programs.
The entire currently active environment variables list of running process is copied for the new process by Windows on starting a new process. The Windows kernel library function CreateProcess does this environment variables list copy from the memory of the current process to the memory of the new process on function parameter lpEnvironment (long pointer to environment) being a null pointer. One of the CreateProcess functions is always used on Windows on starting an executable from another executable.
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 and Security – System – Advanced system settings - Environment Variables 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 with a processor supporting also the x86 instruction set. 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 the fully 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.
That reason is responsible for external command SORT not being found on execution of the batch file which contains somewhere above set path=....
9. LOCAL variable PATH is too long.
The local variable PATH of cmd.exe is too long. The Windows Command Processor fails to find any executable/script in the folder paths of local Path if the string value is longer than 8191 characters.
Please see my second answer here for more details regarding to length limitations of PATH.
Thanks goes to Albert Mosiałek for informing me about this cause of a not recognized program or script.
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.
I) How to modify system or user PATH?
The system and user PATH environment variables are modified by a user best using the Windows GUI dialog window Environment Variables. This dialog window can be opened as follows:
Click on the Windows Start menu button.
Type on keyboard environment variables.
There are offered by Windows the two items:
Edit the system environment variables
Edit environment variables for your account
Click on one of the two items to open the Environment Variables window.
There can be also opened the Windows Control Panel. There must be next clicked on System and Security with Category selected for display option View by. Next must be clicked System. There must be clicked on left side Advanced system settings and next on the button Environment Variables...
The System window can be opened also by pressing the key combination Windows logo key + Pause if the keyboard has the key Pause at all or at least in combination with the key Fn. See also the Microsoft documentation page Keyboard shortcuts in Windows.
The further user actions are self-explaining for editing either user Path in upper list on existing at all or system Path in lower list.
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.
In my case, I was so sure that I didn't mess with PATH. It was that I wasn't aware that path and PATH are the same. CMD is case insensitive.
This answer contains additional information to my first answer here regarding to length limitations of PATH.
There are not good coded executables/scripts which modify system or user PATH without checking first if the folder path to add is not already in string value of one of the two PATH environment variables as reported by Albert Mosiałek in a comment. Multiple executions of such a program results in local PATH string value of cmd.exe becomes longer and longer until reaching the PATH length limitations.
The maximum length of local PATH string value of cmd.exe depends on version of Windows and multiple string length limitations.
Length limitations of PATH on Windows Vista and Windows 7
Length limitations of system PATH
The system PATH as stored in Windows registry is truncated to its maximum length of 4095 characters before expanding all the environment variable references. The truncated string assigned to local PATH of cmd.exe can be also shorter than 4095 characters on system PATH contains environment variable references like %SystemRoot% (12 characters) expanding to C:\Windows (10 characters) and no user PATH is stored in Windows registry.
The system PATH is truncated to its maximum length of 4095 characters after expansion of the environment variable references. The truncated string assigned to local PATH of cmd.exe can be longer than the string value stored in Windows registry if environment variable references expand to strings which are longer than the environment variable reference strings.
In worst case the system PATH is truncated twice to a maximum length of 4095 characters, the first time before and the second time after expansion of the environment variable references.
Length limitations of user PATH
The user PATH is ignored completely independent on length of system PATH if the string value stored in Windows registry is longer than 4095 characters.
The user PATH is appended with an additional semicolon in expanded form to local PATH of cmd.exe on being in Windows registry not longer than 4095 characters even if the user PATH is in expanded form longer than 4095 characters because of environment variable references like %APPDATA%, %LOCALAPPDATA% or %USERPROFILE%.
The local PATH of cmd.exe can reach the maximum length of 8191 characters in worst case with a very long and perhaps already once or twice truncated system PATH and a user PATH not longer than 4095 characters in Windows registry, but longer than 4095 characters in expanded form.
The Windows Command Processor cmd.exe stops finding any executable on local PATH becomes too long, for example if the system PATH of 4095 characters in registry expands to a string with 4087 characters and is concatenated with a semicolon and a user Path stored in Windows registry with 4074 characters, but is expanded to a string value of length 4104 characters, resulting in a local Path with a total length of 8192 characters. There is not even found anymore any executable in %SystemRoot%\System32 on local PATH string value has a length of 8192 characters although the execution of set path outputs the local PATH with first directory path C:\Windows\System32.
There is the Command prompt (Cmd. exe) command-line string limitation which means that the environment variable name PATH plus equal sign = plus the variable string value plus the string terminating null byte must fit into a character array of 8192 characters. The string value of the local environment variable PATH as output on running set path in a command prompt window cannot be longer than 8186 characters for that reason although in memory the string value of local Path can be up to 8191 characters.
The internal command SET of cmd.exe does not output anymore a line-feed on running set path in a command prompt window if the local PATH has a string value of 8186 or more characters. In the console window is displayed for that reason in this case the environment variable PATHEXT with the equal sign and its string value appended to end of the string value of the environment variable PATH.
Length limitations of Control Panel windows for editing environment variables
A user or system PATH or any other in Windows registry persistent stored environment variable with a string value longer than 4094 characters is not displayed in the Environment Variables dialog window. For a user it looks like the environment variable does not exist which has a string value with more than 4094 characters although the environment variable is stored in registry and is perhaps even defined in local environment of running processes. The other user and system variables are still displayed in the Environment Variables window.
The Edit User Variable and Edit System Variable dialog windows display a Variable value with up to 4094 characters. A user can delete characters from such a long string value and save the shortened string value. But a user cannot append characters or replace existing characters on string value of the environment variable is longer than 2047 characters. A user can edit for that reason a user or system environment variable PATH with a string value longer than 2047 characters only for removal of a directory path using the Environment Variables window of Control Panel, but not for changing characters of an existing directory path or adding one more directory path to the environment variable string which is longer than 2047 characters.
Recommendations for PATH lengths
The system as well as the user PATH as stored in Windows registry and in their expanded form should be never longer than 4094 characters on Windows Vista and Windows 7 and are best both shorter than 2048 characters to be editable in the Control Panel windows.
Length limitations of PATH on Windows XP
Length limitations of system PATH
The system PATH as stored in Windows registry is truncated to its maximum length of 2047 characters before expanding all the environment variable references. The truncated string assigned to local PATH of cmd.exe can be also shorter than 2047 characters on system PATH contains environment variable references like %SystemRoot% (12 characters) expanding to C:\Windows (10 characters) and no user PATH is stored in Windows registry.
The system PATH is truncated to its maximum length of 2047 characters after expansion of the environment variable references. The truncated string assigned to local PATH of cmd.exe can be longer than the string value stored in Windows registry if environment variable references expand to strings which are longer than the environment variable reference strings.
In worst case the system PATH is truncated twice to a maximum length of 2047 characters, the first time before and the second time after expansion of the environment variable references.
Length limitations of user PATH
The user PATH is ignored completely if the expanded system PATH concatenated with the expanded user PATH with an additionally inserted semicolon results in a string value longer than 2047 characters. The maximum length of the user PATH on Windows XP depends for that reason on current length of expanded system PATH.
Length limitations of Control Panel windows for editing environment variables
A user or system PATH or any other in Windows registry persistent stored environment variable with a string value longer than 4095 characters is not displayed in the Environment Variables dialog window. For a user it looks like the environment variable does not exist which has a string value of more than 4095 characters although the environment variable is stored in registry and is perhaps even defined truncated in the local environment of running processes. The other user and system variables are still displayed in the Environment Variables window.
The Edit User Variable and Edit System Variable dialog windows display a Variable value with up to 2047 characters. A user can edit an even longer string value and save the string value, but the string value is always truncated to a maximum length of 2047 characters as displayed in edit field of the window. A user cannot append characters or replace existing characters on string value of the environment variable is longer than 2047 characters.
Recommendations for PATH lengths
The system PATH as stored in Windows registry and in its expanded form should be never longer than 2047 characters on Windows XP.
The user PATH in its expanded form should be short enough to be not ignored on concatenating it with the system PATH.
We can use setx as discussed here.
setx PATH "%PATH%;C:\Something\bin"
But this command can just make changed to user PATH variable not the system one.
How can we make a similar system wide command?
Type setx /? to get basic command help. You'll easily discover:
/M Specifies that the variable should be set in
the system wide (HKEY_LOCAL_MACHINE)
environment. The default is to set the
variable under the HKEY_CURRENT_USER
environment.
You need to run this from an elevated command prompt. Right-click the cmd shortcut and select Run as Administrator.
E.g.
setx /M PATH "%PATH%;C:\Something\bin"
Caution:
We may destroy the current system's PATH variable. Make sure you backup its value before you modify it.
From powershell
setx /M PATH "$($env:path);c:\program files\mynewprogram"
Solution when dealing with a >1024 char path:
None of the other answers worked in my case, but using pathed did the trick. You can append to path as simply as this:
pathed /append C:\Path\To\Be\Added /machine
You can check if the edit happened correctly by running
pathed
PS: if you want to change the user's path instead use:
pathed /append C:\Path\To\Be\Added /user
and pathed /user to check if it went through correctly.
PPS: In order to be able to run pathed from terminal, you need to put the exe in a directory already on your path (or add a new directory to path, but then you you might need to open a new instance of cmd.exe in order for the new path to be recognized)
One problem with %PATH%, is it includes the user's path. If you don't mind Powershell, you can run the following
$p = [Environment]::GetEnvironmentVariable("PATH", [EnvironmentVariableTarget]::Machine);
[Environment]::SetEnvironmentVariable("PATH", $p + ";C:\MyPath", [EnvironmentVariableTarget]::Machine);
If you want to add some location to the PATH environment variable on user level, use the following on the command line:
setx PATH ^%PATH^%;"C:\Program Files\Something\bin"
Why the strange syntax?
First, you do not want to expand the system PATH variable but keep it as a symbol, otherwise you will not participate in future additions to the system PATH variable. Therefore, you have to quote the % characters with ^.
If you use this in a command script, you have to use double %% instead of ^%.
The " encloses a string that contains spaces. If you do not have spaces, you can omit the quotes.
The added string has to follow directly without space so the whole thing forms a single argument to the setx command.
Please refer to Adding a directory to the PATH environment variable in Windows
append_user_path.cmd
append_system_path.cmd
- both work just fine
I want the user to input the path of the bin directory and then store that path to system variable path
i tried this
set /p path = Please specify the path to the bin folder
echo Path is set to = %path%
does not seems to work
Basically i want the user to enter the path and that entered path gets permanently stored in the system variable 'path' hope i am more clear now
You may get help from the answer of this question: Setting a system environment variable from a Windows batch file?
It says you should use setx
Remove the spaces. The set command doesn't trim, so the input is actually stored in a variable named path<space>.
This is something you should be able to spot easily if you call set without parameters. You will see an extra variable that has this extra space.
BUT NOTE: path is already an existing variable, containing the search path for the command session. You'd better use a different name altogether if you don't want to overwrite that variable.