linux - Prevent entering duplicate records in file using Shell Script -


i creating 1 sh file in user enters roll number, name, subject name , marks. , storing in 1 text file. don't want user enter same roll number again. if enters same roll number should throw message. here have done:

read -p "enter roll: " roll read -p "enter name: " name read -p "enter subject: " sub read -p "enter mark: " mark echo "$roll $name $sub $mark" >> asd.txt

how prevent entering duplicate roll number.

touch asd.txt rollexists=1 while [ $rollexists != 0 ]     read -p "enter roll: " roll     rollexists=`grep -e "^${roll} " asd.txt | wc -l`     if [[ "$rollexists" != "0" ]]                 echo "roll exists"     fi done read -p "enter name: " name read -p "enter subject: " sub read -p "enter mark: " mark echo "$roll $name $sub $mark" >> asd.txt

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