until [ 條件判斷 ]
do
    # 循環(huán)體
    命令1
    命令2
    ...
done

      +------------------+
      |   執(zhí)行 until     |
      +------------------+
               |
               v
      +------------------+
      | 條件是否為真？    |<---+
      +------------------+   |
            /     \         |
         是/       \否       |
          v         v       |
    +---------+  +-----------+
    | 退出循環(huán) |  | 執(zhí)行循環(huán)體 |
    +---------+  +-----------+
                     |
                     +------->（回到條件判斷）

#!/bin/bash

i=1

until [ $i -gt 5 ]
do
    echo "當(dāng)前數(shù)字: $i"
    i=$((i + 1))
done

i=1
until [ $i -gt 5 ]; do
    echo $i
    i=$((i+1))
done

i=1
while [ $i -le 5 ]; do
    echo $i
    i=$((i+1))
done

#!/bin/bash

echo "等待 MySQL 服務(wù)啟動(dòng)..."

until nc -z localhost 3306
do
    echo "MySQL 未啟動(dòng)，5秒后重試..."
    sleep 5
done

echo "MySQL 已啟動(dòng)，繼續(xù)后續(xù)操作。"

#!/bin/bash

input=""

until [ -n "$input" ]
do
    read -p "請(qǐng)輸入用戶名: " input
    if [ -z "$input" ]; then
        echo "輸入不能為空，請(qǐng)重新輸入。"
    fi
done

echo "歡迎你，$input！"

#!/bin/bash

max_retries=3
attempt=1

until ping -c1 example.com &>/dev/null || [ $attempt -gt $max_retries ]
do
    echo "第 $attempt 次嘗試失敗，正在重試..."
    attempt=$((attempt + 1))
    sleep 2
done

if [ $attempt -le $max_retries ]; then
    echo "網(wǎng)絡(luò)連接成功！"
else
    echo "錯(cuò)誤：無法連接網(wǎng)絡(luò)，已重試 $max_retries 次。"
fi

i=1
until [ $i -gt 2 ]
do
    j=1
    until [ $j -gt 3 ]
    do
        echo "i=$i, j=$j"
        j=$((j + 1))
    done
    i=$((i + 1))
done

i=1
until [ $i -gt 5 ]
do
    if [ $i -eq 3 ]; then
        i=$((i + 1))
        continue  # 跳過本次循環(huán)
    fi

    if [ $i -eq 5 ]; then
        break  # 提前退出循環(huán)
    fi

    echo "當(dāng)前值: $i"
    i=$((i + 1))
done