What is the proper way to test if a parameter is empty in a batch file

Question

I need to test if a variable is set or not   I ve tried several techniques but they seem to fail whenever  1 is surrounded by quotes such as the case when  1 is  quot c  some path with spaces quot   IF NOT  1 GOTO MyLabel    This is invalid syntax IF  quot  1 quot      quot  quot  GOTO MyLabel    Works unless  1 has double quotes which fatally kills bat execution IF  1    GOTO MyLabel    Gives an unexpected GOTO error   According to this site  these are the supported IF syntax types  So  I don t see a way to do it  IF  NOT  ERRORLEVEL number command IF  NOT  string1  string2 command IF  NOT  EXIST filename command  UPDATE  on 2020-10-25  I updated the accepted answer from using brackets to using a tilde   Everyone says the tilde is better as it s more secure   I m a little torn cause the tilde looks more complicated and is less clear as to what it s purpose is but nevertheless  I changed it

User · Answer

You can use   if defined  variable  echo That s defined  if not defined  variable  echo Nope  Undefined

User · Answer

Use  IF DEFINED variable command  to test variable in batch file   But if you want to test batch parameters  try below codes to avoid tricky input  such as  1 2  or ab  cd   set tmp   1  if   tmp                   echo empty   else       echo not empty

User · Answer

You can use   IF    1        GOTO MyLabel   to strip the outer set of quotes   In general  this is a more reliable method than using square brackets because it will work even if the variable has spaces in it

User · Answer

One of the best semi solutions is to copy  1 into a variable and then use delayed expansion  as delayedExp  is always safe against any content     set  param1   1  setlocal EnableDelayedExpansion if   param1         echo it is empty   rem     or use the DEFINED keyword now if defined param1 echo There is something   The advantage of this is that dealing with param1 is absolutly safe     And the setting of param1 will work in many cases  like  test bat hello this is a test test bat you  amp me   But it still fails with strange contents like  test bat   amp   amp    To be able to get a 100  correct answer for the existence  It detects if  1 is empty  but for some content it can t fetch the content  This can be also be useful to distinguish between an empty  1 and one with     It uses the ability of the CALL command to fail without aborting the batch file    echo off setlocal EnableDelayedExpansion set  arg1   call set  arg1   1   if defined arg1 goto  arg exists  set  arg1    call set  arg1   1  if   arg1   EQU           echo arg1 exists  but can t assigned to a variable     REM Try to fetch it a second time without quotes      call set arg1   1      goto  arg exists    echo arg1 is missing exit  b   arg exists echo arg1 exists  perhaps the content is   arg1     If you want to be 100  bullet proof to fetch the content  you could read How to receive even the strangest command line parameters

User · Answer

To sum things up   set str   1 if not defined str   echo Empty string     This code will output  Empty string  if  1 is either    or   or empty  Added it to the accepted answer that s currently incorrect

User · Answer

Script 1   Input   Remove Quotes cmd   This is a Test     ECHO OFF  REM Set  string  variable to  first  command line parameter SET STRING  1  REM Remove Quotes  Only Remove Quotes if NOT Null  IF DEFINED STRING SET STRING  STRING      REM IF  1  or String  is NULL GOTO MyLabel IF NOT DEFINED STRING GOTO MyLabel   REM   OR   IF     equals     GOTO MyLabel IF   STRING           GOTO MyLabel  REM GOTO End of File GOTO  EOF   MyLabel ECHO Welcome   PAUSE   Output  There is none   1 was NOT blank  empty  or NULL      Run   Remove Quotes cmd   without any parameters with the above script 1  Output   1 is blank  empty  or NULL    Welcome   Press any key to continue           Note  If you set a variable inside an IF     ELSE     statement  it will not be available to DEFINED until after it exits the  IF  statement  unless  Delayed Variable Expansion  is enabled  once enabled use an exclamation mark     in place of the percent     symbol    For example   Script 2   Input   Remove Quotes cmd   This is a Test     ECHO OFF  SETLOCAL EnableDelayedExpansion  SET STRING  0 IF 1  1     SET STRING  1   ECHO String in IF Statement   STRING     ECHO String in IF Statement  delayed expansion    STRING       ECHO String out of IF Statement   STRING    REM Remove Quotes  Only Remove Quotes if NOT Null  IF DEFINED STRING SET STRING  STRING      ECHO String without Quotes  STRING    REM IF  1 is NULL GOTO MyLabel IF NOT DEFINED STRING GOTO MyLabel  REM GOTO End of File GOTO  EOF   MyLabel ECHO Welcome   ENDLOCAL PAUSE   Output   C  Users Test gt  C  Users Test Documents Batch Files Remove Quotes cmd   This is a Test    String in IF Statement   C  Users Test Documents Batch Files Remove Quotes cmd     String in IF Statement  delayed expansion    This is a Test     String out of IF Statement   This is a Test     String without Quotes This is a Test    C  Users Test gt        Note  It will also remove quotes from inside the string   For Example  using script 1 or 2       C  Users Test Documents Batch Files  Remove Quotes cmd   This is  a  Test   Output  Script 2    String in IF Statement   C  Users Test Documents Batch Files Remove Quotes cmd     String in IF Statement  delayed expansion    This is  a  Test     String out of IF Statement   This is  a  Test     String without Quotes This is a Test       Execute   Remove Quotes cmd   without any parameters in Script 2   Output   Welcome   Press any key to continue

User · Answer

Using   instead of   for empty string checking   echo off SET a  SET b Hello IF   a         echo String a is empty IF   b         echo String b is empty

User · Answer

Use square brackets instead of quotation marks   IF   1        GOTO MyLabel   Parentheses are insecure  only use square brackets

User · Answer

I usually use this   IF   1        GOTO MyLabel   If  1 is empty  the IF will compare     to     which will evaluate to true

User · Answer

I ve had a lot of issues with a lot of answers on the net  Most work for most things  but there s always a corner case that breaks each one  Maybe it doesn t work if it s got quotes  maybe it breaks if it doesn t have quotes  syntax error if the var has a space  some will only work on parameters  as opposed to environment variables   other techniques allow an empty set of quotes to pass as  defined   and some trickier ones won t let you chain an else afterward   Here s a solution I m happy with  please let me know if you find a corner case it won t work for      ifSet if    1       Exit  B 1  else  Exit  B 0    Having that subroutine either in a your script  or in it s own  bat  should work  So if you wanted to write  in pseudo    if  var  then something else somethingElse   You can write    Call  ifSet  var   amp  amp        Echo something             Echo something else       It worked for all my tests    Call  ifSet  amp  amp  ECHO y     ECHO n  Call  ifSet a  amp  amp  ECHO y     ECHO n  Call  ifSet     amp  amp  ECHO y     ECHO n  Call  ifSet  a   amp  amp  ECHO y     ECHO n  Call  ifSet  a a   amp  amp  ECHO y     ECHO n   Echo d n  y  n  y  y    More examples    Wanna just check if  Call  ifSet  var   amp  amp  Echo set Just if not  only the else   Call  ifSet  var     Echo set Checking a passed argument  works fine  Call  ifSet  1  amp  amp  Echo set Didn t want to clog up your scripts dupe code  so you put it in it s own ifSet bat  No problem    Call ifSet bat  var    amp  amp  Echo set      Echo not set

User · Answer

Unfortunately I don t have enough reputation to comment or vote on the current answers to I ve had to write my own   Originally the OP s question said  variable  rather than  parameter   which got very confusing  especially as this was the number one link in google for searching how to test for blank variables   Since my original answer  Stephan has edited the original question to use the correct terminology  but rather than deleting my answer I decided to leave it to help clear up any confusion  especially in case google is still sending people here for variables too    1 IS NOT A VARABLE   IT IS A COMMAND LINE PARAMETER   Very important distinction   A single percent sign with a number after it refers to a command line parameter not a variable   Variables are set using the set command  and are recalled using 2 percent signs - one before and one after   For example  myvar   To test for an empty variable you use the  if not defined  syntax  commands explicitly for variables do not require any percent signs   for example   set myvar1 foo   if not defined myvar1 echo You won t see this because  myvar1  is defined    if not defined myvar2 echo You will see this because  myvar2  isn t defined     If you want to test command line parameters then I recommend referring to jamesdlin s answer

User · Answer

Empty string is a pair of double-quotes     we can just test the length   set ARG  1 if not defined ARG goto nomore  set CHAR  ARG  2 1  if defined CHAR goto goon   then test it s 2 characters against double-quotes   if   ARG  1 1        if   ARG  0 1        goto blank   else goto goon   Here s a batch script you can play with  I think it properly catches the empty string   This is just an example  you just need to customize 2  or 3   steps above according to your script    echo off if not   OS     Windows NT  goto EOF    I guess we need enableExtensions  CMIIW setLocal enableExtensions set i 0 set script  0   LOOP set  a i  i  1  set A1  1 if not defined A1 goto nomore     Assumption     Empty string is  exactly  a pair of double-quotes          Step out if str length is more than 2 set C3  A1  2 1  if defined C3 goto goon     Check the first and second char for double-quotes    Any characters will do fine since we test it  literally  if   A1  1 1        if   A1  0 1        goto blank goto goon   goon echo args  i      1  shift goto LOOP   blank echo args  i      1  is empty string shift goto LOOP   nomore echo  echo command line  echo  script       EOF   This torture test result    test bat          gt    bl      lt     gt                   -            gt   gt      args 1        args 2        is empty string args 3      gt    bl     args 4      lt     gt    args 5            args 6        is empty string args 7        args 8      -      args 9           gt   gt    args 10        is empty string  command line   test bat          gt    bl      lt     gt                   -            gt   gt

User · Answer

From IF         If Command Extensions are enabled IF   changes as follows   IF   I  string1 compare-op string2 command IF CMDEXTVERSION number command IF DEFINED variable command                   The DEFINED conditional works just   like EXISTS except it takes an   environment variable name and returns   true if the environment variable is   defined

User · Answer

I created this small batch script based on the answers here  as there are many valid ones  Feel free to add to this so long as you follow the same format   REM Parameter-testing  Setlocal EnableDelayedExpansion EnableExtensions  IF NOT    1       echo Percent Tilde 1 failed with quotes  ELSE  echo SUCCESS  IF NOT    1       echo Percent Tilde 1 failed with brackets  ELSE  echo SUCCESS  IF NOT    1       echo Quotes one failed  ELSE  echo SUCCESS  IF NOT   1       echo Brackets one failed  ELSE  echo SUCCESS  IF NOT   1         echo Appended dot quotes one failed  ELSE  echo SUCCESS  IF NOT   1         echo Appended dot brackets one failed  ELSE  echo SUCCESS   pause

User · Answer

I test with below code and it is fine    echo off  set varEmpty  if not   varEmpty             echo varEmpty is not empty   else       echo varEmpty is empty   set varNotEmpty hasValue if not   varNotEmpty             echo varNotEmpty is not empty   else       echo varNotEmpty is empty

User · Answer

I got in in just under a month old  even though it was asked 8 years ago     I hope s he s moved beyond batch files by now   -  I used to do this all the time   I m not sure what the ultimate goal is  though   If s he s lazy like me  my go bat works for stuff like that    See below  But  1  the command in the OP could be invalid if you are directly using the input as a command  i e      C  Users Me    is an invalid command  or used to be if you were on a different drive    You need to break it in two parts   C  cd  Users Me   And  2  what does  defined  or  undefined  mean   GIGO   I use the default to catch errors   If the input doesn t get caught  it drops to help  or a default command    So  no input is not an error   You can try to cd to the input and catch the error if there is one   Ok  using go  downloads  only one paren  is caught by DOS   Harsh     cd   1  if  errorlevel  neq 0 goto  error   And  3  quotes are needed only around the path  not the command  i e      cd C  Users     was bad  or used to in the old days  unless you were on a different drive     cd   Users     is functional   cd   Users Dr Whos infinite storage space    works if you have spaces in your path      REM go bat  REM The   sigh prevents echo on the current command  REM The echo on off turns on off the echo command  Turn on for debugging  REM You can t see this   echo off if  help       1  goto  help  if  c       1  C  if  c       1  goto  done  if  d       1  D  if  d       1  goto  done  if  home     1   homedrive  if  home     1  cd  homepath  if  home     1  if  errorlevel  neq 0 goto  error if  home     1  goto  done  if  docs       1  goto  docs   REM goto  help echo Default command cd  1 if  errorlevel  neq 0 goto  error goto  done   help echo  Type go and a code for a location directory echo For example echo go D echo will change disks  D   echo go home echo will change directories to the users home directory   homepath   echo go pictures echo will change directories to  homepath  pictures echo Notes echo   sigh prevents echo on the current command echo The echo on off turns on off the echo command  Turn on for debugging echo Paths  only  with folder names with spaces need to be inclosed in         quotes  not the ommand  goto  done   docs echo executing   homedrive  homepath  Documents   homedrive  cd   homepath  Documents  test error  if  errorlevel  neq 0 goto  error goto  done   error echo Error  Input   1  2  3  4  5  6  7  8  9  or command is invalid echo go help for help goto  done   done

[windows] What is the proper way to test if a parameter is empty in a batch file?

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