#!/bin/bash
 
VarSize=${1-5} # use $1 if defined, else set VarSize as 5
OptSize=${2-3} # use $2 if defined, else set OptSize as 3
HomeSize=${3-2} # use $3 if defined, else set HomeSize as 2
TmpSize=${4-2} # use $4 if defined, else set TmpSize as 2
 
# Here you may have extra code to check if all the above variables are numbers and not something else.
# Left as an exercise to the OP.
 
VarStandard=4
OptStandard=2
HomeStandard=1
TmpStandard=1
 
if (( VarSize > VarStandard )); then # Why pipe it to bc when bash has provision to perform math
    VarAdd=$(( VarSize - VarStandard ))
fi
if (( OptSize > OptStandard )); then
    OptAdd=$(( OptSize - OptStandard ))
fi
if (( HomeSize > HomeStandard )); then
    HomeAdd=$(( HomeSize - HomeStandard ))
fi
if (( TmpSize > TmpStandard )); then
    TmpAdd=$(( TmpSize - TmpStandard ))
fi
  
if (( $(( VarAdd + OptAdd + HomeAdd + TmpAdd )) == 0 )) ; then
    echo "No Space needed"
else
    echo "$(( VarAdd + OptAdd + HomeAdd + TmpAdd )) extra space is needed"
fi