Exiting out of a FOR loop in a batch file

Question

Why does this batch file never break out of the loop  For  L   f In  1 1 1000000  Do  If Not Exist   f Goto  EOF  Shouldn t the Goto  EOF break out of the loop  Edit  I guess I should ve asked more explicitly    how can I break out of the loop

User · Answer

You could simply use echo on and you will see that goto  eof or even exit  b doesn t work as expected     The code inside of the loop isn t executed anymore  but the loop is expanded for all numbers to the end  That s why it s so slow   The only way to exit a FOR  L loop seems to be the variant of exit like the exsample of Wimmel  but this isn t very fast nor useful to access any results from the loop   This shows 10 expansions  but none of them will be executed  echo on for  l   n in  1 1 10  do     goto  eof   echo   n

User · Answer

So I realize this is kind of old  but after much Googling  I couldn t find an answer I was happy with  so I came up with my own solution for breaking a FOR loop that immediately stops iteration  and thought I d share it   It requires the loop to be in a separate file  and exploits a bug in CMD error handling to immediately crash the batch processing of the loop file when redirecting the STDOUT of DIR to STDIN   MainFile cmd  ECHO Simple test demonstrating loop breaking  ECHO  CMD  C   dp0 LOOP cmd ECHO  ECHO After LOOP PAUSE   LOOP cmd  FOR  L   A IN  1 1 10  DO       ECHO   A     IF   A EQU 3 DIR  gt  amp 0 2 gt NUL        When run  this produces the following output  You ll notice that both iteration and execution of the loop stops when  A   3     gt MainFile cmd    gt ECHO Simple test demonstrating loop breaking  Simple test demonstrating loop breaking     gt ECHO      gt CMD  C Z  LOOP cmd    gt FOR  L  A IN  1 1 10  DO   ECHO  A  IF  A EQU 3 DIR         1 gt  amp 0 2 gt NUL      gt   ECHO 1  IF 1 EQU 3 DIR          1 gt  amp 0 2 gt NUL   1    gt   ECHO 2  IF 2 EQU 3 DIR          1 gt  amp 0 2 gt NUL   2    gt   ECHO 3  IF 3 EQU 3 DIR          1 gt  amp 0 2 gt NUL   3    gt ECHO      gt ECHO After LOOP After LOOP    gt PAUSE Press any key to continue         If you need to preserve a single variable from the loop  have the loop ECHO the result of the variable  and use a FOR  F loop in the MainFile cmd to parse the output of the LOOP cmd file   Example  using the same LOOP cmd file as above    MainFile cmd   ECHO OFF ECHO  ECHO Simple test demonstrating loop breaking  ECHO  FOR  F  delims     L IN   CMD  C   dp0 LOOP cmd   DO SET VARIABLE   L ECHO After LOOP ECHO  ECHO  VARIABLE  ECHO  PAUSE   Output     gt MainFile cmd  Simple test demonstrating loop breaking   After LOOP  3  Press any key to continue         If you need to preserve multiple variables  you ll need to redirect them to temporary files as shown below   MainFile cmd   ECHO OFF ECHO  ECHO Simple test demonstrating loop breaking  ECHO  CMD  C   dp0 LOOP cmd ECHO After LOOP ECHO  SET  P VARIABLE1  lt  TEMP  1 SET  P VARIABLE2  lt  TEMP  2 ECHO  VARIABLE1  ECHO  VARIABLE2  ECHO  PAUSE   LOOP cmd   ECHO OFF FOR  L   A IN  1 1 10  DO       IF   A EQU 1 ECHO ONE  gt  TEMP  1     IF   A EQU 2 ECHO TWO  gt  TEMP  2     IF   A EQU 3 DIR  gt  amp 0 2 gt NUL     Output     gt MainFile cmd  Simple test demonstrating loop breaking   After LOOP  ONE TWO  Press any key to continue         I hope others find this useful for breaking loops that would otherwise take too long to exit due to continued iteration

User · Answer

As jeb noted  the rest of the loop is skipped but evaluated  which makes the FOR solution too slow for this purpose  An alternative   set F 1  nextpart if not exist   F   goto  EOF echo  F  set  a F  F  1 goto nextpart   You might need to use delayed expansion and call subroutines when using this in loops

User · Answer

Assuming that the OP is invoking a batch file with cmd exe  to properly break out of a for loop just goto a label   Change this   For  L   f In  1 1 1000000  Do If Not Exist   f Goto  EOF   To this   For  L   f In  1 1 1000000  Do If Not Exist   f Goto fileError    do something    then exit or do somethign else   fileError GOTO EOF   Better still  add some error reporting   set filename  For  L   f In  1 1 1000000  Do      set filename   f     If Not Exist   f set tempGoto fileError      do something    then exit or do somethign else   fileError echo file does not exist   filename   GOTO EOF   I find this to be a helpful site about lesser known cmd exe DOS batch file functions and tricks  https   www dostips com

User · Answer

Based on Tim s second edit and this page you could do this    echo off if   1    loop      for  l   f in  1 1 1000000  do       echo   f     if exist   f exit       goto  eof   cmd  v on  q  d  c   0 loop  echo done   This page suggests a way to use a goto inside a loop  it seems it does work  but it takes some time in a large loop  So internally it finishes the loop before the goto is executed

User · Answer

Did a little research on this  it appears that you are looping from 1 to 2147483647  in increments of 1    1  1  2147483647    The firs number is the starting number  the next number is the step  and the last number is the end number   Edited To Add  It appears that the loop runs to completion regardless of any test conditions   I tested  FOR  L   F IN  1  1  5  DO SET   F 6   And it ran very quickly   Second Edit  Since this is the only line in the batch file  you might try the EXIT command   FOR  L   F IN  1  1  2147483647  DO  IF NOT EXIST   F EXIT   However  this will also close the DOS prompt window

User · Answer

you do not need a seperate batch file to exit a loop using exit  b if you are using call instead of goto like   call  loop  echo loop finished  goto  eof   loop FOR  L   I IN  1 1 10  DO       echo   I     IF   I  5 exit  b     in this case  the  exit  b  will exit the  call  and continue from the line after  call  So the output is this   1 2 3 4 5 loop finished

User · Answer

My answer Use nested for loops to provide break points to the for  l loop   for   a in  0 1 2 3 4 5 6 7 8 9  do      for   b in  0 1 2 3 4 5 6 7 8 9  do         for  l   c in  1 1 10  do            if not exist   a  b  c goto  continue                 continue   Explanation The code must be tweaked significantly to properly use the nested loops   For example  what is written will have leading zeros   Regular  for loops can be immediately broken out of with a simple goto command  where for  l loops cannot   This code s innermost for  l loop cannot be immediately broken  but an overall break point is present after every 10 iterations  as written    The innermost loop doesn t have to be 10 iterations -- you ll just have to account for the math properly if you choose to do 100 or 1000 or 2873 for that matter  if math even matters to the loop      History I found this question while trying to figure out why a certain script was running slowly   It turns out I used multiple loops with a traditional loop structure   set cnt 1  loop if   somecriteria     finished  goto  continue rem do some things here set  a cnt    1 goto  loop   continue echo the loop ran  cnt  times   This script file had become somewhat long and it was being run from a network drive   This type of loop file was called maybe 20 times and each time it would loop 50-100 times   The script file was taking too long to run   I had the bright idea of attempting to convert it to a for  l loop   The number of needed iterations is unknown  but less than 10000   My first attempt was this   setlocal enabledelayedexpansion set cnt 1 for  l   a in  1 1 10000  do      if   somecriteria     finished  goto  continue    rem do some things here    set  a cnt    1     continue echo the loop ran  cnt  times   With echo on  I quickly found out that the for  l loop still did     something     without actually doing anything   It ran much faster  but still slower than I thought it could should   Therefore I found this question and ended up with the nested loop idea presented above      Side note It turns out that the for  l loop can be sped up quite a bit by simply making sure it doesn t have any output   I was able to do this for a noticeable speed increase   setlocal enabledelayedexpansion set cnt 1  for  l   a in  1 1 10000  do       if   somecriteria     finished  goto  continue    rem do some things here    set  a cnt    1    gt  nul   continue echo the loop ran  cnt  times

[batch-file] Exiting out of a FOR loop in a batch file?

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