function pause {
    read -p "$*"
}

function saveToResultsFile {
    echo "$*" > wynik_bg.txt
}

function addToResultsFile {
    echo "$*" >> wynik_bg.txt
}

input_file="./00_15_1101_75.out"
pattern="(?<=\(ev\):).*"
i=1
grep -ohP "$pattern" $input_file | while read -r line ; do
    stringarray=($line)
    homo=${stringarray[0]}
    lumo=${stringarray[1]}
    bg=`echo $lumo-$homo | bc -l`
    echo "$i: $bg"
   	if [[ $i -eq 1 ]]; then
   		saveToResultsFile "$i $bg"
   	else
   		addToResultsFile "$i $bg"
   	fi
    i=$((i+1))
done

pause '[Enter pliz]...'