if [ 條件判斷 ]; then
  # 條件為真時執(zhí)行的代碼塊
fi

#!/bin/bash
TARGET_FILE="/etc/hosts"

if [ -f "$TARGET_FILE" ]; then
  echo "文件 '$TARGET_FILE' 存在。"
fi

if [ 條件判斷 ]; then
  # 條件為真時執(zhí)行的代碼塊
else
  # 條件為假時執(zhí)行的代碼塊
fi

#!/bin/bash
TARGET_DIR="/var/log/non_existent_dir"

if [ -d "$TARGET_DIR" ]; then
  echo "目錄 '$TARGET_DIR' 存在。"
else
  echo "目錄 '$TARGET_DIR' 不存在，將嘗試創(chuàng)建。"
  mkdir -p "$TARGET_DIR"
fi

if [ 條件1 ]; then
  # 條件1為真時執(zhí)行
elif [ 條件2 ]; then
  # 條件1為假，但條件2為真時執(zhí)行
else
  # 以上所有條件都為假時執(zhí)行
fi

#!/bin/bash
HTTP_CODE=200

if [ $HTTP_CODE -eq 200 ]; then
  echo "請求成功 (OK)"
elif [ $HTTP_CODE -eq 404 ]; then
  echo "資源未找到 (Not Found)"
elif [ $HTTP_CODE -eq 500 ]; then
  echo "服務(wù)器內(nèi)部錯誤 (Internal Server Error)"
else
  echo "收到未知的HTTP狀態(tài)碼: $HTTP_CODE"
fi

for variable_name in item1 item2 item3 ...; do
  # 循環(huán)體
done

#!/bin/bash
# 將所有 .txt 文件重命名為 .txt.bak
for filename in *.txt; do
  if [ -f "$filename" ]; then
    echo "正在備份: $filename -> ${filename}.bak"
    mv "$filename" "${filename}.bak"
  fi
done

for (( initialization; condition; step )); do
  # 循環(huán)體
done

#!/bin/bash
TARGET_HOST="8.8.8.8"

for (( i=1; i<=3; i++ )); do
  echo "--- 第 $i 次 PING 測試 ---"
  ping -c 1 "$TARGET_HOST"
done

while [ 條件判斷 ]; do
  # 循環(huán)體
done

#!/bin/bash
CONFIG_FILE="/etc/fstab"

while read -r line; do
  # 忽略注釋和空行
  if [[ "$line" =~ ^# || -z "$line" ]]; then
    continue
  fi
  echo "讀取到配置行: $line"
done < "$CONFIG_FILE"

until [ 條件判斷 ]; do
  # 循環(huán)體
done

#!/bin/bash
PORT=8080
TIMEOUT=10
COUNT=0

until nc -z localhost $PORT >/dev/null 2>&1; do
  if [ $COUNT -ge $TIMEOUT ]; then
    echo "等待端口 $PORT 超時！"
    exit 1
  fi
  echo "端口 $PORT 尚未啟動，等待1秒..."
  sleep 1
  COUNT=$((COUNT + 1))
done

echo "端口 $PORT 已成功啟動！"

#!/bin/bash
for file in /var/log/*; do
  if [ -d "$file" ]; then
    continue # 如果是目錄，則跳過
  fi

  echo "正在處理文件: $file"

  if [ -s "$file" ] && grep -q "ERROR" "$file"; then
    echo "在文件 '$file' 中找到錯誤，停止處理。"
    break # 找到錯誤后，完全停止
  fi
done

case $variable in
  pattern1)
    # 匹配 pattern1 時執(zhí)行
    ;;
  pattern2|pattern3)
    # 匹配 pattern2 或 pattern3 時執(zhí)行
    ;;
  *)
    # 默認情況，當以上模式都不匹配時執(zhí)行
    ;;
esac

#!/bin/bash
ACTION=$1

case $ACTION in
  start)
    echo "正在啟動服務(wù)..."
    # systemctl start my_service
    ;;
  stop)
    echo "正在停止服務(wù)..."
    # systemctl stop my_service
    ;;
  status)
    echo "檢查服務(wù)狀態(tài)..."
    # systemctl status my_service
    ;;
  *)
    echo "用法: $0 {start|stop|status}"
    exit 1
    ;;
esac

#!/bin/bash
if [ -z "$1" ]; then
  echo "用法: $0 <文件名>"
  exit 1
fi

if [ -r "$1" ] && [ -w "$1" ] && [ -x "$1" ]; then
  echo "Full permissions granted"
else
  echo "Permissions incomplete"
fi

#!/bin/bash
ENVIRONMENT="production"
FORCE_DEPLOY="false"

if [[ "$ENVIRONMENT" == "production" && "$FORCE_DEPLOY" != "true" ]]; then
  echo "Safety check passed: Not a forced production deploy."
  exit 0
else
  echo "Proceeding with deployment."
fi

#!/bin/bash
for (( num=10; num<=20; num+=2 )); do
  echo $num
done

#!/bin/bash
for logfile in /var/log/*.log; do
  if [ -s "$logfile" ]; then
    echo "找到非空日志文件: $(basename "$logfile")"
  fi
done

#!/bin/bash
echo "請輸入內(nèi)容 (輸入 'quit' 退出):"
while read -r input_line; do
  if [ "$input_line" == "quit" ]; then
    break
  fi
  echo "你輸入了: $input_line"
done

#!/bin/bash
LOG_FILE_TO_CHECK="my_app.log"
touch $LOG_FILE_TO_CHECK # 創(chuàng)建一個空文件用于測試

echo "正在監(jiān)控 '$LOG_FILE_TO_CHECK' ..."
# 在另一個終端執(zhí)行 echo "critical error" >> my_app.log 來觸發(fā)
until grep -q "critical error" "$LOG_FILE_TO_CHECK"; do
  sleep 2
done

echo "Critical error detected!"

#!/bin/bash
for (( i=1; i<=3; i++ )); do
  echo "外層循環(huán): i=$i"
  for (( j=1; j<=3; j++ )); do
    echo "  內(nèi)層循環(huán): j=$j"
    if [ $i -eq $j ]; then
      echo "  i 等于 j，跳出所有循環(huán)！"
      break 2 # '2' 表示跳出兩層循環(huán)
    fi
  done
done

#!/bin/bash
FILENAME="archive-2023.tar.gz"

case $FILENAME in
  *.log)
    echo "Log file"
    ;;
  *.tar.gz|*.tgz)
    echo "Compressed archive"
    ;;
  *.sh)
    echo "Shell script"
    ;;
  *)
    echo "Unknown file type"
    ;;
esac

#!/bin/bash
PS3="請選擇一個操作 (輸入數(shù)字): "
options=("Start" "Stop" "Restart" "Exit")

select opt in "${options[@]}"; do
  case $opt in
    "Start")
      echo "正在啟動..."
      ;;
    "Stop")
      echo "正在停止..."
      ;;
    "Restart")
      echo "正在重啟..."
      ;;
    "Exit")
      echo "退出腳本。"
      break
      ;;
    *)
      echo "無效選項 '$REPLY'，請重新選擇。"
      ;;
  esac
done