Linux中关于流程控制条件判断、循环作业

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for ((i=1;i<=9;i++))
do
    for((j=1;j<=i;j++))
    do
        echo-n-e"$j*$i=`echo $(($j*$i))`t"
    done
    echo""
done

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read -p "Please enter your score:" score
if [ -z $score ]
then
    echo "you must input your score"
    exit 1
fi

expr $score + 1 &> /dev/null
exit_code=$?
[ $exit_code -ne 0 ] && {
    echo "Please enter an integer!!"
    exit 2
}

if [ $score -lt 0 -o $score -gt 100 ]
then
    echo "Please enter the correct score!!"
    exit 3
fi

if [ $score -ge 85 ]
then
    echo "LEVEL A "
elif [ $score -ge 70 ]
then
    echo "LEVEL B"
elif [ $score -ge 60 ]
then
    echo "LEVEL C"
else
    echo "LEVEL D"
fi

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for user in `seq -f "user%02g" 1 20`
do
    echo $user
done