Write by lyc at 2018-10-21
Update by lyc at 2021-3-18：整理自己早期的word版本到markdown

一、shell case条件语句

1.shell if语法

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case "${PARM}" in
value1)
     command
     ;;
value2)
     command
     ;;
*)
     command
     exit 1
esac

2.例：控制脚本传参

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$ cat sync.sh 
#!/bin/sh

# 控制传入参数个数
[ $# -ne 1 ]&&{
    echo "$0"
    echo "USAGE: /bin/sh $0 {(A|a)|(B|b)}"
    exit 1
}

function main(){
     choice=${1}
     case "${choice}" in
     A|a)
          # command
          ;;
     B|b)
          # command
          ;;
     *)
          echo "USAGE: ${choice} not in the case." 
          exit 1
     esac
}

main $*