Check if bash variable equals 0

Question

I have a bash variable depth and I would like to test if it equals 0  In case yes  I want to stop executing of script  So far I have   zero 0   if    depth -eq  zero    then     echo  false       exit  fi   Unfortunately  this leads to       -eq  unary operator expected    might be a bit inaccurate due to translation   Please  how can I modify my script to get it working

User · Answer

Looks like your depth variable is unset  This means that the expression    depth -eq  zero   becomes   -eq 0   after bash substitutes the values of the variables into the expression  The problem here is that the -eq operator is incorrectly used as an operator with only one argument  the zero   but it requires two arguments  That is why you get the unary operator error message   EDIT  As Doktor J mentioned in his comment to this answer  a safe way to avoid problems with unset variables in checks is to enclose the variables in     See his comment for the explanation    if     depth  -eq  0     then    echo  false      exit  fi   An unset variable used with the    command appears empty to bash  You can verify this using the below tests which all evaluate to true because xyz is either empty or unset       if   -z     then echo  true   else echo  false   fi xyz     if   -z   xyz      then echo  true   else echo  false   fi unset xyz  if   -z   xyz      then echo  true   else echo  false   fi

User · Answer

you can also use this format and use comparison operators like        lt       if     total    0     then       echo  No results for   1         return   fi

User · Answer

You can try this       depth  Error Message      when your depth variable is not even declared or is unset    NOTE  Here it s just   after depth   or      depth   Error Message      when your depth variable is declared but is null like   depth       NOTE  Here it s    after depth   Here if the variable depth is found null it will print the error message and then exit

User · Answer

Try    zero 0   if     depth -eq  zero     then   echo  false     exit  fi

User · Answer

Specifically    depth    By example  the following prints 1   declare -i x 0   x    amp  amp  echo  x  x 1   x    amp  amp  echo  x

User · Answer

Double parenthesis           is used for arithmetic operations   Double square brackets           can be used to compare and examine numbers  only integers are supported   with the following operators      NUM1 -eq NUM2 returns true if NUM1 and NUM2 are numerically equal      NUM1 -ne NUM2 returns true if NUM1 and NUM2 are not numerically equal      NUM1 -gt NUM2 returns true if NUM1 is greater than NUM2      NUM1 -ge NUM2 returns true if NUM1 is greater than or equal to NUM2      NUM1 -lt NUM2 returns true if NUM1 is less than NUM2      NUM1 -le NUM2 returns true if NUM1 is less than or equal to NUM2    For example  if     age  gt  21      bad   gt  is a string comparison operator  if    age  gt  21     bad   gt  is a redirection operator  if     age -gt 21      okay  but fails if  age is not numeric  if     age  gt  21      best    on age is optional

[bash] Check if bash variable equals 0

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