shell 使用摘记

1.一直有点搞不清shell里面的判断，反引号，echo。看下面例子，

文件sedTest.yml内容：

server:
    url: http://testjkweb.tourongjia.com
spring:
  aop:
ddsdsd
      auto: true
      proxy-target-class: false
  redis:

代码：

match_flag=echo `grep -q "^spring" "/home/vobile/test/sedTest.yml"`

echo `$match_flag|wc -l`

if `grep -q "^spring" "/home/vobile/test/sedTest.yml"`; then
        echo "matching"
fi


if $match_flag; then
        echo "match"
else
        echo "not match"
fi

if [ `grep -q "^spring" "/home/vobile/test/sedTest.yml"` ]; then

        echo "matched 1"
fi


if [ $match_flag ]; then

        echo "matched 2"
fi

结果：

1
matching

match
matched 2

可以看到，if `grep -q "^spring" "/home/vobile/test/sedTest.yml"` 和if $match_flag的结果相同，都能匹配

而 if [ `grep -q "^spring" "/home/vobile/test/sedTest.yml"` ] 和 if [ $match_flag ] 的结果不同， if [ `grep -q "^spring" "/home/vobile/test/sedTest.yml"` ]不能匹配,??

 

3.if [ ! `grep "^$key" "$CONFIG_FILE_PATH/$path"` ];

这种代码要小心，如果`grep "^$key" "$CONFIG_FILE_PATH/$path"`返回字符串中有空格则会得到不匹配的结果，正确的做法

      t=`grep "^$key" "$CONFIG_FILE_PATH/$CONFIG_FILE"`
                echo $t"aaa"
                if [ ! "$t" ]; then
                        echo  "$CONFIG_FILE_PATH/$CONFIG_FILE不完整,$key项缺失"
                        exit 2
                fi

就是字符串要用“”括起来

 

 4. /tmp/$$中字符串是david.test = ${david.test}

for key in $(awk -F "=" '{print $2}' /tmp/$$) ; do
                echo "key=$key"

结果：${david.test}key，前面空格被忽略了
但换另外一种写法

 change_value=`echo $line | awk -F= '{gsub(/^( |\t)*|( |\t)*$/,"",$2);print $2}'`
  echo "change_value=$change_value"

结果：change_value= ${david.test}，表明空格不被省略，看起来是反引号和$符在具体的应用中有所区别