Shell ternary operation (detailed case)

• Common ternary operations in other grammars:

  表达式 ? 表达式 : 表达式 ;
  

• shellThere is also a similar way in :

  command1 && command2 || command3
  

  If commandis a series of combinations, you can use { }to commandsenclose. Note: If the code block is used in a function,  { } the last one must be ;

  command1 && {
        
         command2_1; command2_2; command2_3; } || {
        
         command3_1; command3_3; command3_3; }
  

• example

  #!/bin/bash
  
  res="mp-weixin"
  
  iswx=$([[ $res =~ "weixin" ]] && echo 1 || echo 0)
  
  echo "$iswx"
  

  # fileName 文件不存在，则退出，就可以按照下面方式执行
  [ -e $fileName ] || {
        
         echo -e "fileName Not existed!"; exit 1; }
  
  #也或者可以增加一些 log 打印信息
  [ -e $fileName ] && echo -e "$fileName existed" || {
        
         echo -e "$fileName Not existed!"; exit 1; }
  
  #多个命令集合的组合
  [ -e $fileName ] && echo -e "$fileName existed"; ehco -e "Other Necessary Information" || {
        
         echo -e "$fileName Not existed!"; exit 1; }
  [ -e $fileName ] && {
        
         echo -e "$fileName existed"; ehco -e "Other Necessary Information"; } || {
        
         echo -e "$fileName Not existed!"; exit 1; }
  
  #读取IP地址，若为空，则使用默认IP，否则使用新的IP地址
  read -p "Please input Management IP (Default is $DEFAULT_IP): " MGMT_IP 
  [[ -z $MGMT_IP ]] && {
        
         MGMT_IP=$DEFAULT_IP; echo -e "Using default IP $MGMT_IP\n" ;} || DEFAULT_IP=$MGMT_IP