LInux：循环语句

• if-else语句

  • if 语句语法格式

    if [ $a -gt $b ];
    then echo "a>b"
    fiif [ $a -gt $b ];
    then echo "a>b"echo "a!=b"echo "true"
    fi
    

• if-else语句

  • if-else 语句语法格式

    if [ $a -gt $b ];
    then echo "a>b"
    elseecho "a<=b"
    fiif [ $a -gt $b ];
    then echo "a>b"echo "a!=b"echo "true"
    elseecho "a<=b"
    fiif ((a>b));
    then echo "true"echo "a>b"
    elseecho "a<=b"
    fi
    

  • if else语法格式

    if [ $a -gt $b ];
    then echo "a>b"
    elif [$a -eq $b]
    thenecho "a=b"
    elseecho "a<b"
    fi
    

• for 循环

  • for循环一般格式为

    for m in 1 2 3 4;
    do echo "values is $m"
    donefor n in This is a dong;
    do echo $n 
    done
    

• while 语句

  • while 循环语法格式

    int=5
    while(($int>=2));
    do echo "$int"let "int--"
    doneecho "按下CTRL+D退出"
    echo "输入你喜欢的电影"
    while read film;
    doecho "${film} is ok"
    done
    

• 无限循环

  while True;
  doecho "ok"
  donefor ((::))
  

• until循环

  • until 循环执行一系列命令直至条件为 true 时停止

    a=0
    until [ ! $a -lt 10 ];
    doecho $aa=$((a+1))
    done
    

• case … esac

  echo "输入1到4之间的数字"
  read -p "数字：" num
  case $num in 1) echo '1';;2) echo '2';;3) echo '3';;4) echo '4';;
  esac   s1='iambot'
  case $s1 in'iambot') echo 'bot';;'iampm') echo 'pm';;'iampl') echo 'pl';;
  esac 
  

• 跳出循环

  • break 命令允许跳出所有循环

    echo "welcome to Amusement park"
    echo "please inter a number between 1-4"
    while :
    doread -p "please inter your number: " numcase $num in1|2|3|4)echo "you choose 1-4 you are great";;*)echo "you choose others you are bad"break;;esac
    done
    

  • continue 命令不会跳出所有循环，仅仅跳出当前循环。

    echo "welcome to Amusement park"
    echo "please inter a number between 1-4"
    while :
    doread -p "please inter your number: " numcase $num in1|2|3|4)echo "you choose 1-4 you are great";;*)echo "you choose others you are bad"continueecho 'game over';;esac
    done
    #运行代码发现，当输入大于5的数字时，该例中的循环不会结束，语句 echo "游戏结束" 永远不会被执行。