shell程序设计的流程控制

if 条件命令串
then
    条件为真时的命令串
else
    条件为假时的命令串
fi

#！/bin/bash
if[ "$1" = "" ] || [ "$2" = "" ]
then
    echo "Please enter file name"
    exit 1
fi
if [ -e $2 ]
then
    echo "The file already exists"
    until [ ! -f $2 ]
    do
        sleep 1
    done
fi
if [ ! 'mv $1 $2']
then
    echo "mv successful"
else
    echo "mv error"
fi

for 变量名
[in数值列表]
do
若干个命令行
done

#！/bin/bash
counter=0
for file in *
do
    counter='expr $counter+1'
done
echo "There are $counter files in 'pwd' we need to process"

while
若干个命令 1
do
若干个命令 2
done

until
若干个命令行1
do
若干个命令行2
done

#！/bin/bash
echo -n "Please enter number:"
read n
sd=0
rev=""
on=$n
echo "$n"
while [ $n -gt 0]
do
    sd=$(($n % 10)) # get Remainder
    n=$(($n % 10)) # get next digit
    rev=$(echo $rev$sd)
done
echo "on in a reverse order $rev"

exp-1)
若干个命令行 1
；；
exp-2)
若干个命令行 2
；；
...
*)
其他命令行
esac

#！/bin/bash
echo "Hit a key,then hit return."
read Keypess 
case "$Keypress" in
[A-Z] echo "Upprercase letter";;
[a-z] echo "Lowercase letter";;
[0-9] echo "Digit";;
*) echo "Punctuation", whitespace,or other";