鸟哥的Linux私房菜 第13章 学习shell script

第13章 学习shell script

13.4 条件判别式

# if XXX; then XXX elif XXX; then XXX else fi 
filename='shiyang.txt'
if [ -f $filename ]; then
    echo -e "$filename is a regular file."
elif [ -d $filename ]; then
    echo -e "$filename is a directory." 
else
    echo -e "err."
fi

#while XXX do XXX done 
a=1
b=1
LIMIT=$((2*2))
while [ "$b" -lt "$LIMIT" ] && [ "$a" -lt "$LIMIT" ]
do
    tmp=$(($a + $b))
    a=$b
    b=$tmp
done
echo $a $b

# for XX in YY do ZZ done    
files=$(ls -a)
for file in $files
do
    if [ -f "$file" ]; then
        echo "$file is a regular file."
    elif [ -d "$file" ]; then
        echo "$file is a directory"
    else
        echo "$file: unknowed type."
    fi
done

#for XX do YY done
END=4
for ((i=0;i<"$END";i++))
do
    echo $i
done

#case esac
read -p "please enter username:  " username
case $username in
    "shiyang")
    echo "$username exists: normal user."
    ;;
    
    "heanni")
    echo "$username exists: normal user."
    ;;
    
    "root")
    echo "$username exists: superuser."
    ;;
    *)
    echo "$username does not exist."
    ;;

esac