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Bourne/bash shell scripts: string comparison

To determine if the value of a variable ($var) is empty (null):

Code:

if [ $var == "" ] 
then 
  echo variable is null 
fi

To determine if the value of a variable is not empty:

Code:

if [ $var != "" ] 
then 
  echo variable is not null 
fi

To compare the contents of a variable to a fixed string:

Code:

if [ $var == "value" ] 
then 
   echo is the same 
fi

To determine if variable's contents are not equal to a fixed string:

Code:

if [ $var != "value" ] 
then 
  echo not the same 
fi

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