Batch Programming Local Commands
How to Use SetLocal and EndLocal in Windows and MS-DOS Batch Files
Dec 19, 2007
Batch file programming is a very useful way to automate small, repetitive, tasks. For those who are new to creating batch files, the Windows Command Line Programming tutorial is a good starting place to read about the basics of batch file programming.
When a batch file is executed, it can be made to do so within its own environment of local parameters. These include environment variables such as PATH which can be set within the context of the batch file (for convenience) and then allowed to revert afterwards, or upon request.
The SETLOCAL Command
The SETLOCAL command is used to specify that the batch script is about to make some changes to the various environment variables (such as PATH) which should be kept local to the current context. Any changes to PATH that is done between the SETLOCAL command and the end of the batch file will be temporary, and only applicable within the local context.
This includes the possibility to change the extension settings - using enableextensions and disableextensions - that are available. Assuming that they are supported under the command line being used, they will be turned on and off, respectively, for the local context.
The local context can be ended by using the ENDLOCAL command.
The ENDLOCAL Command
This command should be paired with a SETLOCAL command that appears before it, logically, within the batch script. There can be several SETLOCAL / ENDLOCAL pairs within a single batch file, but they can not be nested. In other words, there should never be two SETLOCAL commands executed one after the other.
The ENDLOCAL command can be used to terminate the local context before the end of the file is reached.
Testing for Command Extensions
Since the SETLOCAL command accepts the enableextensions parameter to turn command extensions on (with disableextensions providing the opposite effect), and returns an errorlevel result, it can be used to check for command extensions. Some implementations of a DOS-like operating system (like DR-DOS or FreeDOS) might not support extensions, which are enabled by default under Microsoft Windows XP and other command line implementations.
Note : under the MS-DOS command line, Microsoft stipulates that a nonzero value indicates an error.
Checking for extensions is a two step process:
- Pass an invalid command to set errorlevel to 1
- Use SETLOCAL enableextensions to reset errorlevel to 0
If, after carrying out the above, the errorlevel is still set to 1, then command extensions are not available. A good choice of a reasonably non-volatile command to use is the VERIFY command, that just verifies whether files are correctly written or not. So, using the following will cause errorlevel to be set to 1 because the parameter passed is invalid:
VERIFY banana 2>nul
After this, the SETLOCAL command can be used, followed by a test of the errorlevel, as detailed in the Batch File Programming IF Commands article.
Other Batch File Commands
- Batch Programming Echo Command
- Batch File Programming IF Commands
- Batch File Programming FOR Command
- Using Batch Labels, Goto and Call in Batch Programming
