How to use random in BATCH script?

Question

There is a very interesting post on SuperUser related to random numbers in batch scripts worth being referenced here... — aschipfl
– aschipfl, Commented Aug 27, 2015 at 23:47

mousio · Accepted Answer · 2011-04-25 10:46:14Z

155

%RANDOM% gives you a random number between 0 and 32767.

Using an expression like SET /A test=%RANDOM% * 100 / 32768 + 1, you can change the range to anything you like (here the range is [1…100] instead of [0…32767]).

answered Apr 25, 2011 at 10:46

mousio

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4 Comments

mousio Over a year ago

Given the specific problem, you will very likely be using some kind of loop? Then you should indeed be using delayed expansion e.g. via SETLOCAL ENABLEDELAYEDEXPANSION and using !RANDOM! instead of %RANDOM%, like Eugene posted.

mousio Over a year ago

A more general expression would be %RANDOM% * (%maxval% - %minval% + 1) / 32768 + %minval%; just set minval and maxval to the appropriate values first.

mousio Over a year ago

4 Comments

CherryDT Over a year ago

Note that this will not be uniformly distributed! Taking the 0~99 example, the numbers 0~67 will occur slightly more often than the numbers 68~99 because 32767 modulo 100 is 67 and not 0 as it would have to be for a uniform distribution. (This %random% %%100 is no magic syntax but actually %random % %% 100 with one less space, where the %% is just an escaped % which stands for modulo.)

Calmarius Over a year ago

I'm getting "Missing operand" error when trying this on Windows 10. Looks like you need just a singe % for modulo.

Ike Starnes Over a year ago

@Calmarius If you use this on the command line then you need 1 %. In a .BAT file you need 2. That's because in a .BAT file, %100 has special meaning, which is the 100th argument to the .bat file when executed with arguments.

Neil Over a year ago

@IkeStarnes Actually Batch can only access arguments up to %9; %100 means %1 with two zeros suffixed.

indiv · Accepted Answer · 2011-04-28 18:50:38Z

22

You'll probably want to get several random numbers, and may want to be able to specify a different range for each one, so you should define a function. In my example, I generate numbers from 25 through 30 with call:rand 25 30. And the result is in RAND_NUM after that function exits.

@echo off & setlocal EnableDelayedExpansion

for /L %%a in (1 1 10) do (
        call:rand 25 30
        echo !RAND_NUM!
)

goto:EOF

REM The script ends at the above goto:EOF.  The following are functions.

REM rand()
REM Input: %1 is min, %2 is max.
REM Output: RAND_NUM is set to a random number from min through max.
:rand
SET /A RAND_NUM=%RANDOM% * (%2 - %1 + 1) / 32768 + %1
goto:EOF

answered Apr 28, 2011 at 18:50

indiv

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Comments

Evgeny Gavrin · Accepted Answer · 2011-04-25 10:21:34Z

7

@echo off & setLocal EnableDelayedExpansion

for /L %%a in (1 1 100) do (
echo !random!
)

answered Apr 25, 2011 at 10:21

Evgeny Gavrin

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Comments

Jacob · Accepted Answer · 2013-07-14 12:45:52Z

7

set /a number=%random% %% [maximum]-[minimum]

example "

set /a number=%random% %% 100-50

will give a random number between 100 and 50. Be sure to only use one percentage sign as the operand if you are not using the line in a batch script!

answered Jul 14, 2013 at 12:45

Jacob

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1 Comment

kilves76 Over a year ago

On Windows 10 it gives numbers from -50 to 49, as it should. Did it ever really do otherwise?

calebhk98 · Accepted Answer · 2018-09-17 20:55:56Z

7

You could do it this way, which does not require EnableDelayedExpansion

:choosenamea
cls
set /a choosemname=%random%

if %choosemname% GTR %max% goto choosenameb
if %choosemname% LSS %min% goto choosenameb
goto gotnamenow

where max is your max and min is your minimum. This is not very efficient since might take a lot of rounds if your range is too small. Also, this will not work for numbers larger than 32767.

edited Sep 17, 2018 at 20:55

user6250760

answered Apr 13, 2014 at 0:15

calebhk98

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Comments

Yan · Accepted Answer · 2018-05-14 13:35:27Z

4

If you will divide by some large value you will get a huge amount of duplicates one after other. What you need to do is to take modulo of the %RANDOM% value:

@echo off
REM 
SET maxvalue=10
SET minvalue=1

SETLOCAL 
SET /A tmpRandom=((%RANDOM%)%%(%maxvalue%))+(%minvalue%)
echo "Tmp random: %tmpRandom%"
echo "Random:  %RANDOM%"
ENDLOCAL

answered May 14, 2018 at 13:35

Yan

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Comments

Community · Accepted Answer · 2014-02-25 12:14:47Z

3

@echo off
title Professional Hacker
color 02
:matrix
echo %random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%
echo %random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%% 
echo %random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%
echo %random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%
echo %random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%
echo %random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%
echo %random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%% 
echo %random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%% 
goto matrix

edited Feb 25, 2014 at 12:14

CommunityBot

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answered Dec 26, 2013 at 23:12

Sinji58

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1 Comment

Sinji58 Over a year ago

give this some spaces so it has it lines, like @echo off

user3542843 · Accepted Answer · 2014-04-16 20:19:08Z

3

Let's say you want a number 1-5; you could use the following:

    :LOOP
    set NUM=%random:~-1,1%
    if %NUM% GTR 5 (
    goto LOOP )
    goto NEXT

Or you could use :~1,1 in place of :~-1,1. The :~-1,1 is not needed, but it greatly reduces the amount of time it takes to hit the right range. Let's say you want a number 1-50, we need to decide between 2 digits and 1 digit. Use:

    :LOOP
    set RAN1=%random:~-1,1%
    if %RAN1% GTR 5 (
    goto 1 )
    if %RAN1%==5 (
    goto LOOP )
    goto 2

    :1
    set NUM=%random:~-1,1%
    goto NEXT

    :2
    set NUM=%random:~-1,2%
    goto NEXT

You can add more to this algorithm to decide between large ranges, such as 1-1000.

answered Apr 16, 2014 at 20:19

user3542843

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1 Comment

Max Leske Over a year ago

Why would you use goto when you can have one liners like above? Other solutions let you explicitly specify the range. What is the advantage of your code?

simple · Accepted Answer · 2014-12-27 07:19:45Z

1

@(IF not "%1" == "max" (start /MAX cmd /Q /C %0 max&X)ELSE set C=1&set D=2&wmic process where name="cmd.exe" CALL setpriority "REALTIME">NUL)&CLS
:Y
title %random%6%random%%random%%random%%random%9%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%&color %D%&ECHO %random%%C%%random%%random%%random%%random%6%random%9%random%%random%%random%%random%%random%%random%%random%%random%%random%&(IF %C% EQU 46 (TIMEOUT /T 1 /NOBREAK>nul&set C=1&CLS&IF %D% EQU 9 (set D=1)ELSE set /A D=%D%+1)ELSE set /A C=%C%+1)&goto Y

simplified with multiple IF statements and plenty of ((()))

answered Dec 27, 2014 at 7:19

simple

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Comments

strance · Accepted Answer · 2017-08-06 13:43:30Z

And just to be completely random for those who don't always want a black screen.

@(IF not "%1" == "max" (start /MAX cmd /Q /C %0 max&X)ELSE set A=0&set C=1&set V=A&wmic process where name="cmd.exe" CALL setpriority "REALTIME">NUL)&CLS
:Y
(IF %A% EQU 10 set A=A)&(IF %A% EQU 11 set A=B)&(IF %A% EQU 12 set A=C)&(IF %A% EQU 13 set A=D)&(IF %A% EQU 14 set A=E)&(IF %A% EQU 15 set A=F)
(IF %V% EQU 10 set V=A)&(IF %V% EQU 11 set V=B)&(IF %V% EQU 12 set V=C)&(IF %V% EQU 13 set V=D)&(IF %V% EQU 14 set V=E)&(IF %V% EQU 15 set V=F)
(IF %A% EQU %V% set A=0)
title %A%%V%%random%6%random%%random%%random%%random%9%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%&color %A%%V%&ECHO %random%%C%%random%%random%%random%%random%6%random%9%random%%random%%random%%random%%random%%random%%random%%random%%random%&(IF %C% EQU 46 (TIMEOUT /T 1 /NOBREAK>nul&set C=1&CLS&SET /A A=%random% %%15 +1&SET /A V=%random% %%15 +1)ELSE set /A C=%C%+1)&goto Y

This will change screen color also both are random.

Nerdroid · Accepted Answer · 2014-12-29 06:04:23Z

0

now featuring all the colors of the dos rainbow

@(IF not "%1" == "max" (start /MAX cmd /Q /C %0 max&X)
  ELSE set C=1&set D=A&wmic process where name="cmd.exe" CALL setpriority "REALTIME">NUL)&CLS
:Y
set V=%D%

(IF %V% EQU 10 set V=A) 
    & (IF %V% EQU 11 set V=B)
    & (IF %V% EQU 12 set V=C)
    & (IF %V% EQU 13 set V=D) 
    & (IF %V% EQU 14 set V=E)
    & (IF %V% EQU 15 set V=F)
title %random%6%random%%random%%random%%random%9%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%&color %V%&ECHO %random%%C%%random%%random%%random%%random%6%random%9%random%%random%%random%%random%%random%%random%%random%%random%%random%
&(IF %C% EQU 46 (TIMEOUT /T 1 /NOBREAK>nul&set C=1&CLS&IF %D% EQU 15 (set D=1)ELSE set /A D=%D%+1)
  ELSE set /A C=%C%+1)&goto Y

edited Dec 29, 2014 at 6:04

Nerdroid

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answered Dec 29, 2014 at 5:02

randomized

11

1 Comment

Christian Sirolli Over a year ago

I think that is broken

zask · Accepted Answer · 2016-01-25 18:18:30Z

here is a example i created for you, it should display a dialog asking you to select a number 1-10, depending on the number you select, it will generate a random number example to a batch file that you named. If you select "1" then you will get a random 1 digit number example. if you select "10" then you will get a random 10 digit number example.

@echo off
color f0
set /p "FileName= Enter Filename (Without Extension) : "
echo @echo off >> %FileName%.bat
echo File Created!
pause
cls
:CommandLine
set /p "calc= ~%ComputerName%: Enter a number to recieve the amount of  random digits :"
if %calc%==genrand_help goto GenerateRandomHelp
if %calc%==1 echo echo %%RANDOM:~-1%% >> %FileName%.bat
if %calc%==2 echo echo %%RANDOM:~-1%%%%RANDOM:~-1%% >> %FileName%.bat 
if %calc%==3 echo echo %%RANDOM:~-1%%%%RANDOM:~-1%%%RANDOM:~-1%% >>  %FileName%.bat
if %calc%==4 echo echo %%RANDOM:~-1%%%%RANDOM:~-1%%%%RANDOM:~-1%%%%RANDOM:~-1%% >> %FileName%.bat
if %calc%==5 echo echo %%Random%% >> %FileName%.bat
if %calc%==6 echo echo %%Random%%%%RANDOM:~-1%% >> %FileName%.bat
if %calc%==7 echo echo %%Random%%%%RANDOM:~-1%%%%RANDOM:~-1%% >> %FileName%.bat 
if %calc%==8 echo echo %%Random%%%%RANDOM:~-1%%%%RANDOM:~-1%%%%RANDOM:~-1%% >> %FileName%.bat
if %calc%==9 echo echo  %%Random%%%%RANDOM:~-1%%%%RANDOM:~-1%%%%RANDOM:~-1%%%%RANDOM:~-1%% >>  %FileName%.bat
if %calc%==10 echo echo %%Random%%%%Random%% >> %FileName%.bat  
goto CommandLine

randomized · Accepted Answer · 2017-08-06 16:36:05Z

And just to be completely random, a total lack of order: SET /A V=%random% %%15 +1

@(IF not "%1" == "max" (start /MAX cmd /Q /C %0 max&X)ELSE set C=1&set V=A&wmic process where name="cmd.exe" CALL setpriority "REALTIME">NUL)&CLS
:Y
(IF %V% EQU 10 set V=A)&(IF %V% EQU 11 set V=B)&(IF %V% EQU 12 set V=C)&(IF %V% EQU 13 set V=D)&(IF %V% EQU 14 set V=E)&(IF %V% EQU 15 set V=F)
title %V%%random%6%random%%random%%random%%random%9%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%%random%&color %V%&ECHO %random%%C%%random%%random%%random%%random%6%random%9%random%%random%%random%%random%%random%%random%%random%%random%%random%&(IF %C% EQU 46 (TIMEOUT /T 1 /NOBREAK>nul&set C=1&CLS&SET /A V=%random% %%15 +1)ELSE set /A C=%C%+1)&goto Y

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