batch script to launch node app disappears after execution

Question

This node app for work starts up with a starter script in batch. The cmd window stays there after launch and it opens up the correct port, but it always launched the browser too fast so it showed a 404. After npm launched you could refresh the page and it launches fine.

@echo off
@setlocal

set NODE_HOME=%~dp0/nodejs
set PATH=%NODE_HOME%;%PATH%

call npm install
start http://localhost:8090/
call npm start

I wanted to tweak this a bit to have it wait a few seconds before launching the browser. So I figured I just need to open localhost after npm start is outputting "ready for work" to the CLI. But that command actually never 'finishes' so open localhost is never executed. I tried to resolve it like this:

@echo off
@setlocal

SET NODE_HOME=%~dp0/nodejs
SET PATH=%NODE_HOME%;%PATH%

CALL npm install
START /B CMD /C CALL openlocalhost8090.cmd
CALL npm start

And this is what openlocalhost.cmd looks like:

@echo off

TIMEOUT /T 5 /NOBREAK >NUL
START http://localhost:8090/

It actually launches fine and it waits in the background at the same time as npm start is executed so the browser launches without 404 and the app runs fine! But now that I'm testing it again the cmd window disappears after launching the browser. This is quite inconvenient because I'd still like to see log output and be able to stop the server by closing the cmd window. That's how it was with the original script. I need to go into task management to find the process to stop it now.

How can I fix this to make the cmd window stay alive?

Also, is there a better way to handle this 404 "bug"? (I love bash, I could just use open localhost:8090 & npm start and be done!)

Edit: After suggestions by @Mofi this is what I came up with:

@echo off
@setlocal

SET NODE_HOME=%~dp0nodejs
SET PATH=%NODE_HOME%;%PATH%

CALL "%NODE_HOME%\npm.cmd" install
START /B CMD /K CALL openlocalhost8090.cmd
CALL "%NODE_HOME%\npm.cmd" start

I still do the subscript with openlocalhost8090.cmd because contrary to what @Mofi claims that just putting open localhost and call npm start under each other will solve my issue, it doesn't. Putting everything directly under each other is what was wrong with the first script and what I wanted to solve. The browser is started too fast so it 404's before npm can start. If this is not what you meant @Mofi, then I'm sorry but I didn't find your answer very clearly written.

The /K flag after CMD however prevents the cmd window from closing and solves that issue, so thank you for that!

Mofi · Answer 1 · 2023-08-12T16:39:17.007

1. Complete definition of execution environment for batch file

The usage of just @setlocal results in creating a copy of existing list of environment variables, pushing current directory path on stack as well as the states of command extensions and delayed expansion without changing the state for command extensions and of delayed environment variable expansion. So the command is incomplete to define completely the execution environment for the batch file. The execution environment still depends on what is defined for command extensions and delayed expansion outside the batch file which is in general not good for any batch file.

The perfect command line to define execution environment is for this batch file:

setlocal EnableExtensions DisableDelayedExpansion

2. Correct variable definition using batch file path

The command line set NODE_HOME=%~dp0/nodejs is not good because of

\ is the directory separator on Windows and not / as on Linux/Mac as it can be read in Microsoft documentation about Naming Files, Paths, and Namespaces and
%~dp0 expands to a path always ending already with a backslash and for that reason no additional backslash should be added on concatenating the full batch file path with a file/folder name or a wildcard pattern which Windows has to remove later on every usage of the path containing now inside \\ and
the entire argument string of command SET is not enclosed in double quotes which results in this command line does more than just assigning a folder path to environment variable NODE_HOME on full path of batch file contains by chance one or more & like on folder path being C:\Temp\Development & Test which is interpreted by cmd.exe outside a double quoted argument string as a command operator explained in detail on single line with multiple commands using Windows batch file.

The perfect command line is as follows after making sure the command extensions are enabled and delayed environment variable expansion is disabled:

set "NODE_HOME=%~dp0nodejs"

An ampersand in full path of batch file is interpreted here as literal character in double quoted argument string of command SET.

It is important on writing a batch file how a command line looks after Windows command processor parsed it and replaced all environment variable, loop variable and batch file argument references and not how the command line is written in batch file. This command line does not contain an & in batch file, but it can contain & on execution of the command line after replacing %~dp0 by full path of batch file.

It is possible to see how the command line looks after parsing by cmd.exe by running a batch file from within an opened command prompt window with @echo off removed or commented out temporarily to get displayed also the command lines finally executed.

3. Correct modification of local environment variable PATH

set PATH=%NODE_HOME%;%PATH% is again not good as it results in undefined behavior if the string assigned to either environment variable NODE_HOME or environment variable PATH contains an ampersand. The perfect and safe command line (on valid PATH string) would be:

set "PATH=%NODE_HOME%;%PATH%"

4. Referencing executables and scripts with full qualified file names

It is always best to reference executables and scripts in a batch file with full qualified file name on being well known instead of just file name as in this case cmd.exe does not need to search for the file in current directory and all directories listed in local environment variable PATH for a file with an extension listed in local environment variable PATHEXT.

Please take a look on answer on What is the reason for "X is not recognized as an internal or external command, operable program or batch file"? for details.

A batch file referencing executables and scripts with full qualified file names works also on PATH corrupted somehow by an installer or a user, and works also if there are (mainly batch) files created with a file name identical to a Windows command which is used in the batch file, but found by chance by cmd.exe instead of the executable in %SystemRoot%\System32.

So with batch file npm.cmd stored in subdirectory nodejs of batch file directory it would be better to use as replacement for the last three command lines:

call "%NODE_HOME%\npm.cmd" install
call "%NODE_HOME%\npm.cmd" start
start "" "http://localhost:8090/"

5. No need for an additional batch file

It is unclear why another command processor instance is started running parallel to the cmd.exe instance processing the batch file after calling batch file npm.cmd with argument install which is processing one more batch file which runs %SystemRoot%\System32\timeout.exe (without file path and file extension) to wait five seconds and then launch default internet browser with a local url as argument as separate process resulting in second started instance of cmd.exe terminating itself.

It should be enough to call npm.cmd with argument start and start default internet browser as separate process with local url as argument after processing of npm.cmd with argument start finished.

So the entire batch file could be:

@echo off
setlocal EnableExtensions DisableDelayedExpansion
set "NODE_HOME=%~dp0nodejs"
set "PATH=%NODE_HOME%;%PATH%"
call "%NODE_HOME%\npm.cmd" install
call "%NODE_HOME%\npm.cmd" start
start "" "http://localhost:8090/"

It could be that call "%NODE_HOME%\npm.cmd" start results in starting an application as separate process or a service which takes some time to initialize completely and for that reason some seconds must be waited before the internet browser is started with the local url which requires that the started application/service is running already. In this case the batch file should be:

@echo off
setlocal EnableExtensions DisableDelayedExpansion
set "NODE_HOME=%~dp0nodejs"
set "PATH=%NODE_HOME%;%PATH%"
call "%NODE_HOME%\npm.cmd" install
call "%NODE_HOME%\npm.cmd" start
%SystemRoot%\System32\timeout.exe /T 5 /NOBREAK >nul
start "" "http://localhost:8090/"

It does not look so according to posted information posted, but in case of call "%NODE_HOME%\npm.cmd" start results in cmd.exe processing the batch file terminates itself because of a command exit without option /B before reaching end of batch file or the processing of the called batch file never finishes because of cmd.exe is waiting for self-termination of a started executable which does not terminate itself, the batch file should be:

@echo off
setlocal EnableExtensions DisableDelayedExpansion
set "NODE_HOME=%~dp0nodejs"
set "PATH=%NODE_HOME%;%PATH%"
call "%NODE_HOME%\npm.cmd" install
start "Launch browser delayed" /MIN %ComSpec% /C %SystemRoot%\System32\timeout.exe /T 5 /NOBREAK >nul & start "" "http://localhost:8090/"
call "%NODE_HOME%\npm.cmd" start

There is no additional batch file needed in any case.

6. Keep command processor running after finishing execution of batch file

Windows executes implicit %ComSpec% /c "Full qualified batch file name" on double clicking a batch file with making the batch file directory the current directory for cmd.exe. The help output on running in a command prompt window cmd /? explains that option /C is for running a command line and close cmd.exe after finishing execution of this command line. This default behavior is not wanted here. The command processor should keep running after batch file execution which requires starting cmd.exe with option /K and the full qualified batch file name.

Therefore a shortcut file (.lnk) file needs to be created on Windows desktop or in Windows start menu or somewhere else and pinned to Windows taskbar which contains in properties:

Target: %SystemRoot%\System32\cmd.exe /K "Full qualified batch file name"
Start in: "Full path of batch file folder"

The property Target can be also:

%ComSpec% /K "Full qualified batch file name"

ComSpec is a system environment variable used even by cmd.exe itself and must be defined always with %SystemRoot%\System32\cmd.exe as it is by Windows default.

In properties of the shortcut file can be configured also the number of lines and columns for the console window opened on running cmd.exe via this shortcut, the font, the text foreground and background colors and much more. It is even possible to define a Shortcut key to launch cmd.exe for processing the batch file from within any application by pressing this key (or combination of keys).