Why does the non-zero and the zero operator both return true in the shell script? This...

   

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Why does the non-zero and the zero operator both return true in the shell script? This makes no sense. Please see the following small script I have written. I set a variable 'zero' to have nothing. I also get the same results if I set 'zero'¹ to "" or zero="" zero= #the below code prints "is not length zero" if [ -n $zero ] ; then echo "$zero is not length zero" ; fi #the below code prints if [ -z $zero ]; then " is length 0" echo "$zero is length 0"; fi Why does the non-zero and the zero operator both return true in the shell script? This makes no sense. Please see the following small script I have written. I set a variable 'zero' to have nothing. I also get the same results if I set 'zero'¹ to "" or zero="" zero= #the below code prints "is not length zero" if [ -n $zero ] ; then echo "$zero is not length zero" ; fi #the below code prints if [ -z $zero ]; then " is length 0" echo "$zero is length 0"; fi