shell字符串的常用操作

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 定义str变量，方便下面的操作演示

• ${#string} 返回$string的长度

  [root@study ~]# echo ${#str}
  20

• ${string:position} 在$string中,从位置position之后开始截取字符串

  [root@study ~]# echo ${str:4}
  is study string

• ${string:position:length} 从$string指定位置开始截取长度为length字符串

  [root@study ~]# echo ${str:5:2}
  is

• ${string#substring} 从$string开头开始删除最短匹配$substring字符串

  [root@study ~]# echo ${str#this}
  is study string

• ${string##substring} 从$string开头开始删除最长匹配$substring字符串

  [root@study ~]# echo ${str##this}
  is study string

• ${string%substring} 从$string结尾开始删除最短匹配$substring字符串

  [root@study ~]# echo ${str%ing}
  this is study str

• ${string%substring} 从$string结尾开始删除最长匹配$substring字符串

  [root@study ~]# echo ${str%%ing}
  this is study str

• ${string/substring/replace} 使用$replace来代替第一个匹配的$substring字符串

  [root@study ~]# echo ${str/is/AAA}
  thAAA is study string

• ${string/#substring/replace} 如果$string前缀匹配$substring，就用 $replace来代替匹配$substring

  [root@study ~]# echo ${str/#th/AAA}
  AAAis is study string

• ${string/#substring/replace} 如果$string后缀匹配$substring，就用 $replace来代替匹配$substring

  [root@study ~]# echo ${str/%ing/AAA}
  this is study strAAA