LInux：循环语句

• if-else语句

  • if 语句语法格式

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

  • if else语法格式

    if [ $a -gt $b ]; then      echo "a>b" elif [$a -eq $b] then     echo "a=b" else     echo "a

• for 循环

  • for循环一般格式为

    for m in 1 2 3 4; do     echo "values is $m" done  for 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--" done  echo "按下CTRL+D退出" echo "输入你喜欢的电影" while read film; do    echo "${film} is ok" done 

• 无限循环

  while True; do   echo "ok" done  for ((::)) 

• 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 ]; do     echo $a     a=$((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 : do     read -p "please inter your number: " num     case $num in         1|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 : do     read -p "please inter your number: " num     case $num in         1|2|3|4)             echo "you choose 1-4 you are great"             ;;         *)             echo "you choose others you are bad"             continue             echo '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。