#!/bin/bash
function getdir(){
    max=0
    DATEPATTERN="^[0-9]*$"
    for element in `ls $1`
    do
        if [[ "$element" =~ $DATEPATTERN ]]
        then
            if [ `expr $max - $element` -lt 0 ]
            then
                max=$element
            fi 
        fi
    done
    
    for element in `ls $1`
    do
        if [[ "$element" =~ $DATEPATTERN ]]
        then
            if [ $max != $element ]
            then
                rm -rf element
            fi 

        fi
    done
}
root_dir="/root/cloud/builds"
getdir $root_dir

var=10      
var1="qwert"   
var2='qwert'

echo $var  #输出 10
echo $var1 #输出 qwert
echo $var2 #输出 qwert

#!/bin/bash
a=10
val='hello world $a'
echo "单引号："$val 

val='hello 'world' $a'
echo "单引号+单引号 = 拼接："$val 

#val='hello \'world\' $a'
#echo $val
#报错：/usercode/file.sh: line 9: unexpected EOF while looking for matching `''

val="hello 'world' $a"
echo "双引号+单引号 = 输出单引号："$val

val="hello "world" $a"
echo "双引号+双引号 = 拼接："$val

val="hello \"world\" $a"
echo "双引号+双引号转义字符 = 输出双引号："$val

val="hello "$a"world"
echo "双引号+变量 = 拼接："$val

单引号：hello world $a
单引号+单引号 = 拼接：hello world $a
双引号+单引号 = 输出单引号：hello 'world' 10
双引号+双引号 = 拼接：hello world 10
双引号+双引号转义字符 = 输出双引号：hello "world" 10
双引号+变量 = 拼接：hello 10world

if condition
then
    ......
elif
then
    ......
else
    ......
fi

for var in item1 item2 ... itemN
do
    command1
    command2
    ...
    commandN
done