How to find whether or not a variable is empty in Bash

Question

How can I check if a variable is empty in Bash

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I have also seen  if    x variable     x     then       which is obviously very robust and shell independent   Also  there is a difference between  empty  and  unset   See How to tell if a string is not defined in a Bash shell script

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if      variable

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You may want to distinguish between unset variables and variables that are set and empty   is empty         local var name   1      local var value     var name       if    -v   var name      then        if    -n   var value      then          echo  set and non-empty         else          echo  set and empty         fi     else        echo  unset      fi    str  foo  empty    is empty str is empty empty is empty none   Result   set and non-empty set and empty unset   BTW  I recommend using set -u which will cause an error when reading unset variables  this can save you from disasters such as  rm -rf  dir   You can read about this and other best practices for a  strict mode  here

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variable       echo empty     variable  value to set if unset

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In Bash at least the following command tests if  var is empty   if    -z   var      then      Do what you want fi   The command man test is your friend

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if     foo  1    then     echo  yes  fi   prints yes if the variable is set    foo  1  will return 1 when the variable is set  otherwise it will return empty string

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The question asks how to check if a variable is an empty string and the best answers are already given for that   But I landed here after a period passed programming in PHP  and I was actually searching for a check like the empty function in PHP working in a Bash shell   After reading the answers I realized I was not thinking properly in Bash  but anyhow in that moment a function like empty in PHP would have been soooo handy in my Bash code   As I think this can happen to others  I decided to convert the PHP empty function in Bash   According to the PHP manual   a variable is considered empty if it doesn t exist or if its value is one of the following            an empty string      0  0 as an integer      0 0  0 as a float       0   0 as a string      an empty array     a variable declared  but without a value   Of course the null and false cases cannot be converted in bash  so they are omitted   function empty       local var   1         Return true if        1     var is a null string     as empty string        2     a non set variable is passed       3     a declared variable or array but without a value is passed       4     an empty array is passed     if test -z   var      then               echo  1               return        Return true if var is zero  0 as an integer or  0  as a string      elif     var     0 2 gt   dev null       then               echo  1               return        Return true if var is 0 0  0 as a float      elif     var     0 0 2 gt   dev null       then               echo  1               return     fi            echo              Example of usage   if empty    var       then         echo  empty      else         echo  not empty  fi    Demo  The following snippet      bin bash  vars              0     0 0      0      1      string             for    i 0  i lt    vars      i      do     var    vars  i         if empty    var           then             what  empty          else             what  not empty      fi     echo  VAR    var   is  what  done  exit   outputs   VAR    is empty VAR  0  is empty VAR  0 0  is empty VAR  0  is empty VAR  1  is not empty VAR  string  is not empty VAR     is not empty   Having said that in a Bash logic the checks on zero in this function can cause side problems imho  anyone using this function should evaluate this risk and maybe decide to cut those checks off leaving only the first one

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To check if variable v is not set   if     v           then    echo  v not set  fi

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This will return true if a variable is unset or set to the empty string        if   -z   MyVar    then    echo  The variable MyVar has nothing in it   elif     -z   MyVar    then    echo  The variable MyVar has something in it   fi

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Presuming Bash   var     if   -n   var     then     echo  not empty  else     echo  empty  fi

[bash] How to find whether or not a variable is empty in Bash?

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