How do SETLOCAL and ENABLEDELAYEDEXPANSION work

Question

I notice in most scripts  the two are usually in the same line as so   SETLOCAL ENABLEDELAYEDEXPANSION   Are the two in fact separate commands and can be written on separate lines   Will setting ENABLEDELAYEDEXPANSION have an adverse effect on a script if it is set on the first lines of the script and not disabled until the end of the script

User · Accepted Answer

ENABLEDELAYEDEXPANSION is a parameter passed to the SETLOCAL command  look at setlocal      Its effect lives for the duration of the script  or an ENDLOCAL      When the end of a batch script is reached  an implied ENDLOCAL is   executed for any outstanding SETLOCAL commands issued by that batch   script    In particular  this means that if you use SETLOCAL ENABLEDELAYEDEXPANSION in a script  any environment variable changes are lost at the end of it unless you take special measures

User · Answer

I think you should understand what delayed expansion is  The existing answers don t explain it  sufficiently  IMHO   Typing SET    explains the thing reasonably well      Delayed environment variable expansion is useful for getting around   the limitations of the current expansion which happens when a line of   text is read  not when it is executed   The following example   demonstrates the problem with immediate variable expansion   set VAR before if   VAR       before        set VAR after     if   VAR       after   echo If you see this  it worked         would never display the message  since the  VAR  in BOTH IF statements   is substituted when the first IF statement is read  since it logically   includes the body of the IF  which is a compound statement   So the IF   inside the compound statement is really comparing  before  with    after  which will never be equal   Similarly  the following example   will not work as expected   set LIST  for  i in     do set LIST  LIST   i echo  LIST        in that it will NOT build up a list of files in the current directory    but instead will just set the LIST variable to the last file found    Again  this is because the  LIST  is expanded just once when the FOR   statement is read  and at that time the LIST variable is empty  So the   actual FOR loop we are executing is   for  i in     do set LIST   i       which just keeps setting LIST to the last file found       Delayed environment variable expansion allows you to use a different   character  the exclamation mark  to expand environment variables at   execution time   If delayed variable expansion is enabled  the above   examples could be written as follows to work as intended   set VAR before if   VAR       before        set VAR after     if   VAR       after   echo If you see this  it worked    set LIST  for  i in     do set LIST  LIST   i echo  LIST     Another example is this batch file    echo off setlocal enabledelayedexpansion set b z1 for   a in  x1 y1  do    set b   a  echo  b 1 2      This prints x2 and y2  every 1 gets replaced by a 2   Without setlocal enabledelayedexpansion  exclamation marks are just that  so it will echo  b 1 2  twice   Because normal environment variables are expanded when a  block  statement is read  expanding  b 1 2  uses the value b has before the loop  z2  but y2 when not set

User · Answer

A real problem often exists because any variables set inside will not be exported when that batch file finishes  So its not possible to export  which caused us issues  As a result  I just set the registry to ALWAYS used delayed expansion  I don t know why it s not the default  could be speed or legacy compatibility issue

User · Answer

The ENABLEDELAYEDEXPANSION part is REQUIRED in certain programs that use delayed expansion  that is  that takes the value of variables that were modified inside IF or FOR commands by enclosing their names in exclamation-marks   If you enable this expansion in a script that does not require it  the script behaves different only if it contains names enclosed in exclamation-marks  LIKE   THESE   Usually the name is just erased  but if a variable with the same name exist by chance  then the result is unpredictable and depends on the value of such variable and the place where it appears   The SETLOCAL part is REQUIRED in just a few specialized  recursive  programs  but is commonly used when you want to be sure to not modify any existent variable with the same name by chance or if you want to automatically delete all the variables used in your program  However  because there is not a separate command to enable the delayed expansion  programs that require this must also include the SETLOCAL part

[cmd] How do SETLOCAL and ENABLEDELAYEDEXPANSION work?

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