Labels

Wednesday, August 27, 2008

Difference between bat and cmd

I've occasionally thought on the difference between cmd and bat, and from an execution point of view I didn’t think there was any. But it turns out a few commands can modify the execution path of batch files, because they modify the errorlevel differently based on whether they were executed as a .bat or .cmd.

The comment that I did find from Microsoft (the source was MZ according to the signature block!)

The differences between .CMD and .BAT as far as CMD.EXE is concerned are: With extensions enabled, PATH/APPEND/PROMPT/SET/ASSOC in .CMD files will set
ERRORLEVEL regardless of error. .BAT sets ERRORLEVEL only on errors.

If you save the text below as test.bat and test.cmd, and then run each from a command prompt, you see two different results. Note that command extensions are enabled by default on XP, a requirement for this behavioural difference.

I saw several references to bat running under 16-bit VDM and cmd running under 32-bit when executed from a shortcut, however I couldn’t reproduce this on XP SP2.

In addition, apparently 9x days and before there was only bat? And then with NT CMD was introduced, and running the same .bat file on 9x and NT definitely had different results, so having two different extensions made it less likely to accidently run a cmd written for NT on a 9x box if you were interoperating between the two. This sounds plausible, but I can't remember those sorts of details that far back.

I hope this doesn’t excite anyone.


::
:: When called from a cmd, 'set' resets errorlevel, whereas when called from a bat the errorlevel from the previous command is returned.
:: The four examples below show this in different ways, two calling a subroutine, and two using a single line.
::
:: :test generates an error by find without any parameters (2)
:: The set command then clears errorlevel when run as a .cmd file, but when run as a .bat, the previous errorlevel is returned
:: 
:: Delayed environment variable expansion is enabled to allow showing ERRORLEVEL, but the same result occurrs if you use don't use delayed expansion (you just can't see the errorlevel)
:: Therefore the single line below with delayed expansion shows the difference in return errorlevel, but the call to the label allows the if..then..else to also show the same results
::
:: The last example uses concatenated commands, with the final command checking errorlevel and using if..else to report the difference
::
:: && - If
:: || - Else
::
:: Comment from msft:
:: The differences between .CMD and .BAT as far as CMD.EXE is concerned are: With extensions enabled, PATH/APPEND/PROMPT/SET/ASSOC in .CMD files will set ERRORLEVEL regardless of error. .BAT sets ERRORLEVEL only on errors. 


@echo off
::setlocal ENABLEEXTENSIONS
setlocal ENABLEDELAYEDEXPANSION

:: Call test, if successful echo cmd, else echo bat
call :test && echo cmd || echo bat

:: Call test, if successful echo cmd with delayed expansion of errorlevel, else echo bat
call :test && echo cmd error: !errorlevel! || echo bat error: !errorlevel! 

:: Generate the error, clear the error, echo the delayed expansion of errorlevel
find 2>nul & set test=test && echo Single-line error: !errorlevel!

:: Generate the error, clear the error, if errorlevel 1 echo BAT, else echo CMD
find 2>nul & set test=test & if errorlevel 1 (echo Run from BAT error) else (echo Run from CMD no error)

goto :EOF

:test

 :: Generate an error
 find 2>nul

 echo      :test %errorlevel%

 :: Set a variable - when called with .cmd the errorlevel is reset
 set test=test
 echo      :test %errorlevel%
::


Wayne's World of IT (WWoIT), Copyright 2008 Wayne Martin.

2 comments:

Kevin Dondrea said...

Of all the sites I found in Google Search, I wasted a lot of time until..... I found the results that mentioned Wayne's World of IT. This is the best and most thorough answer I got.

THANK YOU!! Awesome.

Anonymous said...

In the early days of CMD, it did make a difference - to this day it bothers me to see people name their batch files as .BAT, because many of the advanced functions available with things like set and for were not available if you ran it as a .BAT. I don't know at what point it changed, but I got caught out wrong one day saying it was different, retested it, and found it no longer matters. It still bugs me to see .bat though.....


All Posts

printQueue AD objects for 2003 ClusterVirtualCenter Physical to VirtualVirtual 2003 MSCS Cluster in ESX VI3
Finding duplicate DNS recordsCommand-line automation – Echo and macrosCommand-line automation – set
Command-line automation - errorlevels and ifCommand-line automation - find and findstrBuilding blocks of command-line automation - FOR
Useful PowerShell command-line operationsMSCS 2003 Cluster Virtual Server ComponentsServer-side process for simple file access
OpsMgr 2007 performance script - VMware datastores...Enumerating URLs in Internet ExplorerNTLM Trusts between 2003 and NT4
2003 Servers with Hibernation enabledReading Shortcuts with PowerShell and VBSModifying DLL Resources
Automatically mapping printersSimple string encryption with PowerShellUseful NTFS and security command-line operations
Useful Windows Printer command-line operationsUseful Windows MSCS Cluster command-line operation...Useful VMware ESX and VC command-line operations
Useful general command-line operationsUseful DNS, DHCP and WINS command-line operationsUseful Active Directory command-line operations
Useful command-linesCreating secedit templates with PowerShellFixing Permissions with NTFS intra-volume moves
Converting filetime with vbs and PowerShellDifference between bat and cmdReplica Domain for Authentication
Troubleshooting Windows PrintingRenaming a user account in ADOpsMgr 2007 Reports - Sorting, Filtering, Charting...
WMIC XSL CSV output formattingEnumerating File Server ResourcesWMIC Custom Alias and Format
AD site discoveryPassing Parameters between OpsMgr and SSRSAnalyzing Windows Kernel Dumps
Process list with command-line argumentsOpsMgr 2007 Customized Reporting - SQL QueriesPreventing accidental NTFS data moves
FSRM and NTFS Quotas in 2003 R2PowerShell Deleting NTFS Alternate Data StreamsNTFS links - reparse, symbolic, hard, junction
IE Warnings when files are executedPowerShell Low-level keyboard hookCross-forest authentication and GP processing
Deleting Invalid SMS 2003 Distribution PointsCross-forest authentication and site synchronizati...Determining AD attribute replication
AD Security vs Distribution GroupsTroubleshooting cross-forest trust secure channels...RIS cross-domain access
Large SMS Web Reports return Error 500Troubleshooting SMS 2003 MP and SLPRemotely determine physical memory
VMware SDK with PowershellSpinning Excel Pie ChartPoke-Info PowerShell script
Reading web content with PowerShellAutomated Cluster File Security and PurgingManaging printers at the command-line
File System Filters and minifiltersOpsMgr 2007 SSRS Reports using SQL 2005 XMLAccess Based Enumeration in 2003 and MSCS
Find VM snapshots in ESX/VCComparing MSCS/VMware/DFS File & PrintModifying Exchange mailbox permissions
Nested 'for /f' catch-allPowerShell FindFirstFileW bypassing MAX_PATHRunning PowerSell Scripts from ASP.Net
Binary <-> Hex String files with PowershellOpsMgr 2007 Current Performance InstancesImpersonating a user without passwords
Running a process in the secure winlogon desktopShadow an XP Terminal Services sessionFind where a user is logged on from
Active Directory _msdcs DNS zonesUnlocking XP/2003 without passwords2003 Cluster-enabled scheduled tasks
Purging aged files from the filesystemFinding customised ADM templates in ADDomain local security groups for cross-forest secu...
Account Management eventlog auditingVMware cluster/Virtual Center StatisticsRunning scheduled tasks as a non-administrator
Audit Windows 2003 print server usageActive Directory DiagnosticsViewing NTFS information with nfi and diskedit
Performance Tuning for 2003 File ServersChecking ESX/VC VMs for snapshotsShowing non-persistent devices in device manager
Implementing an MSCS 2003 server clusterFinding users on a subnetWMI filter for subnet filtered Group Policy
Testing DNS records for scavengingRefreshing Computer Account AD Group MembershipTesting Network Ports from Windows
Using Recovery Console with RISPAE Boot.ini Switch for DEP or 4GB+ memoryUsing 32-bit COM objects on x64 platforms
Active Directory Organizational Unit (OU) DesignTroubleshooting computer accounts in an Active Dir...260+ character MAX_PATH limitations in filenames
Create or modify a security template for NTFS perm...Find where a user is connecting from through WMISDDL syntax in secedit security templates

About Me

I’ve worked in IT for over 13 years, and I know just about enough to realise that I don’t know very much.