How to update PATH variable permanently from Windows command line?

Question

You can use:

setx PATH "%PATH%;C:\\Something\\bin"

However, setx will truncate the stored string to 1024 bytes, potentially corrupting the PATH.

/M will change the PATH in HKEY_LOCAL_MACHINE instead of HKEY_CURRENT_USER. In other words, a system variable, instead of the user's. For example:

SETX /M PATH "%PATH%;C:\your path with spaces"

You have to keep in mind, the new PATH is not visible in your current cmd.exe.

But if you look in the registry or on a new cmd.exe with "set p" you can see the new value.

The documentation on how to do this can be found on MSDN. The key extract is this:

To programmatically add or modify system environment variables, add them to the HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Session Manager\Environment registry key, then broadcast a WM_SETTINGCHANGE message with lParam set to the string "Environment". This allows applications, such as the shell, to pick up your updates.

Note that your application will need elevated admin rights in order to be able to modify this key.

You indicate in the comments that you would be happy to modify just the per-user environment. Do this by editing the values in HKEY_CURRENT_USER\Environment. As before, make sure that you broadcast a WM_SETTINGCHANGE message.

You should be able to do this from your Java application easily enough using the JNI registry classes.

I caution against using the command

setx PATH "%PATH%;C:\Something\bin"

to modify the PATH variable because of a "feature" of its implementation. On many (most?) installations these days the variable will be lengthy - setx will truncate the stored string to 1024 bytes, potentially corrupting the PATH (see the discussion here).

(I signed up specifically to flag this issue, and so lack the site reputation to directly comment on the answer posted on May 2 '12. My thanks to beresfordt for adding such a comment)

This Python-script[*] does exactly that:

"""
Show/Modify/Append registry env-vars (ie `PATH`) and notify Windows-applications to pickup changes.

First attempts to show/modify HKEY_LOCAL_MACHINE (all users), and 
if not accessible due to admin-rights missing, fails-back 
to HKEY_CURRENT_USER.
Write and Delete operations do not proceed to user-tree if all-users succeed.

Syntax: 
    {prog}                  : Print all env-vars. 
    {prog}  VARNAME         : Print value for VARNAME. 
    {prog}  VARNAME   VALUE : Set VALUE for VARNAME. 
    {prog}  +VARNAME  VALUE : Append VALUE in VARNAME delimeted with ';' (i.e. used for `PATH`). 
    {prog}  -VARNAME        : Delete env-var value. 

Note that the current command-window will not be affected, 
changes would apply only for new command-windows.
"""

import winreg
import os, sys, win32gui, win32con

def reg_key(tree, path, varname):
    return '%s\%s:%s' % (tree, path, varname) 

def reg_entry(tree, path, varname, value):
    return '%s=%s' % (reg_key(tree, path, varname), value)

def query_value(key, varname):
    value, type_id = winreg.QueryValueEx(key, varname)
    return value

def yield_all_entries(tree, path, key):
    i = 0
    while True:
        try:
            n,v,t = winreg.EnumValue(key, i)
            yield reg_entry(tree, path, n, v)
            i += 1
        except OSError:
            break ## Expected, this is how iteration ends.

def notify_windows(action, tree, path, varname, value):
    win32gui.SendMessage(win32con.HWND_BROADCAST, win32con.WM_SETTINGCHANGE, 0, 'Environment')
    print("---%s %s" % (action, reg_entry(tree, path, varname, value)), file=sys.stderr)

def manage_registry_env_vars(varname=None, value=None):
    reg_keys = [
        ('HKEY_LOCAL_MACHINE', r'SYSTEM\CurrentControlSet\Control\Session Manager\Environment'),
        ('HKEY_CURRENT_USER', r'Environment'),
    ]
    for (tree_name, path) in reg_keys:
        tree = eval('winreg.%s'%tree_name)
        try:
            with winreg.ConnectRegistry(None, tree) as reg:
                with winreg.OpenKey(reg, path, 0, winreg.KEY_ALL_ACCESS) as key:
                    if not varname:
                        for regent in yield_all_entries(tree_name, path, key):
                            print(regent)
                    else:
                        if not value:
                            if varname.startswith('-'):
                                varname = varname[1:]
                                value = query_value(key, varname)
                                winreg.DeleteValue(key, varname)
                                notify_windows("Deleted", tree_name, path, varname, value)
                                break  ## Don't propagate into user-tree.
                            else:
                                value = query_value(key, varname)
                                print(reg_entry(tree_name, path, varname, value))
                        else:
                            if varname.startswith('+'):
                                varname = varname[1:]
                                value = query_value(key, varname) + ';' + value
                            winreg.SetValueEx(key, varname, 0, winreg.REG_EXPAND_SZ, value)
                            notify_windows("Updated", tree_name, path, varname, value)
                            break  ## Don't propagate into user-tree.
        except PermissionError as ex:
            print("!!!Cannot access %s due to: %s" % 
                    (reg_key(tree_name, path, varname), ex), file=sys.stderr)
        except FileNotFoundError as ex:
            print("!!!Cannot find %s due to: %s" % 
                    (reg_key(tree_name, path, varname), ex), file=sys.stderr)

if __name__=='__main__':
    args = sys.argv
    argc = len(args)
    if argc > 3:
        print(__doc__.format(prog=args[0]), file=sys.stderr)
        sys.exit()

    manage_registry_env_vars(*args[1:])

Below are some usage examples, assuming it has been saved in a file called setenv.py somewhere in your current path. Note that in these examples i didn't have admin-rights, so the changes affected only my local user's registry tree:

> REM ## Print all env-vars
> setenv.py
!!!Cannot access HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session   Manager\Environment:PATH due to: [WinError 5] Access is denied
HKEY_CURRENT_USER\Environment:PATH=...
...

> REM ## Query env-var:
> setenv.py PATH C:\foo
!!!Cannot access HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session   Manager\Environment:PATH due to: [WinError 5] Access is denied
!!!Cannot find HKEY_CURRENT_USER\Environment:PATH due to: [WinError 2] The system cannot find the file specified

> REM ## Set env-var:
> setenv.py PATH C:\foo
!!!Cannot access HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session   Manager\Environment:PATH due to: [WinError 5] Access is denied
---Set HKEY_CURRENT_USER\Environment:PATH=C:\foo

> REM ## Append env-var:
> setenv.py +PATH D:\Bar
!!!Cannot access HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session   Manager\Environment:PATH due to: [WinError 5] Access is denied
---Set HKEY_CURRENT_USER\Environment:PATH=C:\foo;D:\Bar

> REM ## Delete env-var:
> setenv.py -PATH
!!!Cannot access HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session   Manager\Environment:PATH due to: [WinError 5] Access is denied
---Deleted HKEY_CURRENT_USER\Environment:PATH

[*] Adapted from: http://code.activestate.com/recipes/416087-persistent-environment-variables-on-windows/

For reference purpose, for anyone searching how to change the path via code, I am quoting a useful post by a Delphi programmer from this web page: http://www.tek-tips.com/viewthread.cfm?qid=686382

TonHu (Programmer) 22 Oct 03 17:57 I found where I read the original posting, it's here: http://news.jrsoftware.org/news/innosetup.isx/msg02129....

The excerpt of what you would need is this:

You must specify the string "Environment" in LParam. In Delphi you'd do it this way:

 SendMessage(HWND_BROADCAST, WM_SETTINGCHANGE, 0, Integer(PChar('Environment')));

It was suggested by Jordan Russell, http://www.jrsoftware.org, the author of (a.o.) InnoSetup, ("Inno Setup is a free installer for Windows programs. First introduced in 1997, Inno Setup today rivals and even surpasses many commercial installers in feature set and stability.") (I just would like more people to use InnoSetup )

HTH

In a corporate network, where the user has only limited access and uses portable apps, there are these command line tricks:

1. Query the user env variables: reg query "HKEY_CURRENT_USER\Environment". Use "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment" for LOCAL_MACHINE.
2. Add new user env variable: reg add "HKEY_CURRENT_USER\Environment" /v shared_dir /d "c:\shared" /t REG_SZ. Use REG_EXPAND_SZ for paths containing other %% variables.
3. Delete existing env variable: reg delete "HKEY_CURRENT_USER\Environment" /v shared_dir.

This script http://www.autohotkey.com/board/topic/63210-modify-system-path-gui/

includes all the necessary Windows API calls which can be refactored for your needs. It is actually an AutoHotkey GUI to change the System PATH easily. Needs to be run as an Administrator.