When used in a batch file, makes all further changes to environment variables local to the current batch file. When used outside of a batch file, does nothing. Can be ended using ENDLOCAL. Exiting a batch file automatically calls "end local". Can be used to create subprograms: see Functions.
Furthermore, can be used to enable delayed expansion like this: "setlocal EnableDelayedExpansion". Delayed expansion consists in the names of variables enclosed in exclamation marks being replaced with their values only after the execution reaches the location of their use rather than at an earlier point.
The following is an example of using delayed expansion in a script that prints the specified number of first lines of a file, providing some of the function of the command "head" known from other operating systems:
@echo off call :myhead 2 File.txt exit /b :: Function myhead :: =============== :: %1 - lines count, %2 - file name :myhead setlocal EnableDelayedExpansion set counter=1 for /f "tokens=*" %%i in (%2) do ( echo %%i set /a counter=!counter!+1 if !counter! gtr %1 exit /b ) exit /b
$ setlocal /? Begins localization of environment changes in a batch file. Environment changes made after SETLOCAL has been issued are local to the batch file. ENDLOCAL must be issued to restore the previous settings. When the end of a batch script is reached, an implied ENDLOCAL is executed for any outstanding SETLOCAL commands issued by that batch script. SETLOCAL If Command Extensions are enabled SETLOCAL changes as follows: SETLOCAL batch command now accepts optional arguments: ENABLEEXTENSIONS / DISABLEEXTENSIONS enable or disable command processor extensions. These arguments takes precedence over the CMD /E:ON or /E:OFF switches. See CMD /? for details. ENABLEDELAYEDEXPANSION / DISABLEDELAYEDEXPANSION enable or disable delayed environment variable expansion. These arguments takes precedence over the CMD /V:ON or /V:OFF switches. See CMD /? for details. These modifications last until the matching ENDLOCAL command, regardless of their setting prior to the SETLOCAL command. The SETLOCAL command will set the ERRORLEVEL value if given an argument. It will be zero if one of the two valid arguments is given and one otherwise. You can use this in batch scripts to determine if the extensions are available, using the following technique: VERIFY OTHER 2>nul SETLOCAL ENABLEEXTENSIONS IF ERRORLEVEL 1 echo Unable to enable extensions This works because on old versions of CMD.EXE, SETLOCAL does NOT set the ERRORLEVEL value. The VERIFY command with a bad argument initializes the ERRORLEVEL value to a non-zero value.