sed -e '/./{H;$!d;}' -e 'x;/CREATE TABLE `suck_t`/!d;q' bak.sql;此命令如何工作？

Question

bak.sql的内容是：

1  -- MySQL dump 10.14  Distrib 5.5.60-MariaDB, for Linux (x86_64)
2  --
3  -- Host: localhost    Database: suck_db
4  -- ------------------------------------------------------
5  -- Server version   5.5.60-MariaDB
6  
7  /*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
8  /*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
9  /*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;
10  /*!40101 SET NAMES utf8 */;
11  /*!40103 SET @OLD_TIME_ZONE=@@TIME_ZONE */;
12  /*!40103 SET TIME_ZONE='+00:00' */;
13  /*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */;
14  /*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;
15  /*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;
16  /*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */;
17  
18  --
19  -- Current Database: `suck_db`
20  --
21  
22  CREATE DATABASE /*!32312 IF NOT EXISTS*/ `suck_db` /*!40100 DEFAULT CHARACTER SET latin1 */;
23  
24  USE `suck_db`;
25  
26  --
27  -- Table structure for table `suck_t`
28  --
29  
30  DROP TABLE IF EXISTS `suck_t`;
31  /*!40101 SET @saved_cs_client     = @@character_set_client */;
32  /*!40101 SET character_set_client = utf8 */;
33  CREATE TABLE `suck_t` (
34    `id` int(10) NOT NULL AUTO_INCREMENT,
35    `name` varchar(30) NOT NULL DEFAULT '',
36    `age` tinyint(4) NOT NULL DEFAULT '0',
37    PRIMARY KEY (`id`)
38  ) ENGINE=InnoDB AUTO_INCREMENT=28 DEFAULT CHARSET=latin1;
39  /*!40101 SET character_set_client = @saved_cs_client */;
40  
41  --
42  -- Dumping data for table `suck_t`
43  --
44  
45  LOCK TABLES `suck_t` WRITE;
46  /*!40000 ALTER TABLE `suck_t` DISABLE KEYS */;
47  INSERT INTO `suck_t` VALUES (1,'tom1',11),(2,'tom2',11),(3,'tom3',11),(4,'tom4',11),(5,'tom5',11),(6,'tom5',11),(7,'tom5',11),(8,'tom5',11),(9,'tom5',11),(10,'tom5',11),(11,'tom5',11),(12,'tom5',11),(13,'tom5',11),(14,'tom5',11),(15,'tom5',11),(16,'tom5',11),(17,'tom5',11),(18,'tom5',11),(19,'tom5',11),(20,'tom5',11),(21,'tom5',11),(22,'tom5',11),(23,'tom5',11),(24,'tom5',11),(25,'tom5',11),(26,'tom5',11),(27,'tom5',11);
48  /*!40000 ALTER TABLE `suck_t` ENABLE KEYS */;
49  UNLOCK TABLES;
50  /*!40103 SET TIME_ZONE=@OLD_TIME_ZONE */;
51  
52  /*!40101 SET SQL_MODE=@OLD_SQL_MODE */;
53  /*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */;
54  /*!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS */;
55  /*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;
56  /*!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS */;
57  /*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */;
58  /*!40111 SET SQL_NOTES=@OLD_SQL_NOTES */;
59  
60  -- Dump completed on 2018-12-12  1:02:27

当我运行时

sed -e '/./{H;$!d;}' -e 'x;/CREATE TABLE `suck_t`/!d;q' bak.sql

输出为：

DROP TABLE IF EXISTS `suck_t`;
/*!40101 SET @saved_cs_client     = @@character_set_client */;
/*!40101 SET character_set_client = utf8 */;
CREATE TABLE `suck_t` (
`id` int(10) NOT NULL AUTO_INCREMENT,
`name` varchar(30) NOT NULL DEFAULT '',
`age` tinyint(4) NOT NULL DEFAULT '0',
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=28 DEFAULT CHARSET=latin1;
/*!40101 SET character_set_client = @saved_cs_client */;

此命令的目的是从bak.sql文件中提取创建表扇区。

我真的很困惑，它是怎么工作的？

还有{H;$!d;}，为什么要有大括号？带牙套和不带牙套有什么区别？

我的理解是，在'/.之后/｛H；$！d；｝'，模式空间包括10个空行和最后一行，保留空间包括所有非空行。即

图案空间为：

1  
2  
3  
4  
5  
6  
7  
8  
9  
10  
11  -- Dump completed on 2018-12-12  1:02:27

等待空间为：

1  -- MySQL dump 10.14  Distrib 5.5.60-MariaDB, for Linux (x86_64)
2  --
3  -- Host: localhost    Database: suck_db
4  -- ------------------------------------------------------
5  -- Server version   5.5.60-MariaDB
6  /*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
7  /*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
8  /*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;
9  /*!40101 SET NAMES utf8 */;
10  /*!40103 SET @OLD_TIME_ZONE=@@TIME_ZONE */;
11  /*!40103 SET TIME_ZONE='+00:00' */;
12  /*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */;
13  /*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;
14  /*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;
15  /*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */;
16  --
17  -- Current Database: `suck_db`
18  --
19  CREATE DATABASE /*!32312 IF NOT EXISTS*/ `suck_db` /*!40100 DEFAULT CHARACTER SET latin1 */;
20  USE `suck_db`;
21  --
22  -- Table structure for table `suck_t`
23  --
24  DROP TABLE IF EXISTS `suck_t`;
25  /*!40101 SET @saved_cs_client     = @@character_set_client */;
26  /*!40101 SET character_set_client = utf8 */;
27  CREATE TABLE `suck_t` (
28    `id` int(10) NOT NULL AUTO_INCREMENT,
29    `name` varchar(30) NOT NULL DEFAULT '',
30    `age` tinyint(4) NOT NULL DEFAULT '0',
31    PRIMARY KEY (`id`)
32  ) ENGINE=InnoDB AUTO_INCREMENT=28 DEFAULT CHARSET=latin1;
33  /*!40101 SET character_set_client = @saved_cs_client */;
34  --
35  -- Dumping data for table `suck_t`
36  --
37  LOCK TABLES `suck_t` WRITE;
38  /*!40000 ALTER TABLE `suck_t` DISABLE KEYS */;
39  INSERT INTO `suck_t` VALUES (1,'tom1',11),(2,'tom2',11),(3,'tom3',11),(4,'tom4',11),(5,'tom5',11),(6,'tom5',11),(7,'tom5',11),(8,'tom5',11),(9,'tom5',11),(10,'tom5',11),(11,'tom5',11),(12,'tom5',11),(13,'tom5',11),(14,'tom5',11),(15,'tom5',11),(16,'tom5',11),(17,'tom5',11),(18,'tom5',11),(19,'tom5',11),(20,'tom5',11),(21,'tom5',11),(22,'tom5',11),(23,'tom5',11),(24,'tom5',11),(25,'tom5',11),(26,'tom5',11),(27,'tom5',11);
40  /*!40000 ALTER TABLE `suck_t` ENABLE KEYS */;
41  UNLOCK TABLES;
42  /*!40103 SET TIME_ZONE=@OLD_TIME_ZONE */;
43  /*!40101 SET SQL_MODE=@OLD_SQL_MODE */;
44  /*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */;
45  /*!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS */;
46  /*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;
47  /*!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS */;
48  /*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */;
49  /*!40111 SET SQL_NOTES=@OLD_SQL_NOTES */;
50  -- Dump completed on 2018-12-12  1:02:27

执行'x'后，保持空间和模式空间被切换，因此模式空间包括所有非空行，保持空间包括一堆空行和最后一行。

图案空间为：

1  -- MySQL dump 10.14  Distrib 5.5.60-MariaDB, for Linux (x86_64)
2  --
3  -- Host: localhost    Database: suck_db
4  -- ------------------------------------------------------
5  -- Server version   5.5.60-MariaDB
6  /*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
7  /*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
8  /*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;
9  /*!40101 SET NAMES utf8 */;
10  /*!40103 SET @OLD_TIME_ZONE=@@TIME_ZONE */;
11  /*!40103 SET TIME_ZONE='+00:00' */;
12  /*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */;
13  /*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;
14  /*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;
15  /*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */;
16  --
17  -- Current Database: `suck_db`
18  --
19  CREATE DATABASE /*!32312 IF NOT EXISTS*/ `suck_db` /*!40100 DEFAULT CHARACTER SET latin1 */;
20  USE `suck_db`;
21  --
22  -- Table structure for table `suck_t`
23  --
24  DROP TABLE IF EXISTS `suck_t`;
25  /*!40101 SET @saved_cs_client     = @@character_set_client */;
26  /*!40101 SET character_set_client = utf8 */;
27  CREATE TABLE `suck_t` (
28    `id` int(10) NOT NULL AUTO_INCREMENT,
29    `name` varchar(30) NOT NULL DEFAULT '',
30    `age` tinyint(4) NOT NULL DEFAULT '0',
31    PRIMARY KEY (`id`)
32  ) ENGINE=InnoDB AUTO_INCREMENT=28 DEFAULT CHARSET=latin1;
33  /*!40101 SET character_set_client = @saved_cs_client */;
34  --
35  -- Dumping data for table `suck_t`
36  --
37  LOCK TABLES `suck_t` WRITE;
38  /*!40000 ALTER TABLE `suck_t` DISABLE KEYS */;
39  INSERT INTO `suck_t` VALUES (1,'tom1',11),(2,'tom2',11),(3,'tom3',11),(4,'tom4',11),(5,'tom5',11),(6,'tom5',11),(7,'tom5',11),(8,'tom5',11),(9,'tom5',11),(10,'tom5',11),(11,'tom5',11),(12,'tom5',11),(13,'tom5',11),(14,'tom5',11),(15,'tom5',11),(16,'tom5',11),(17,'tom5',11),(18,'tom5',11),(19,'tom5',11),(20,'tom5',11),(21,'tom5',11),(22,'tom5',11),(23,'tom5',11),(24,'tom5',11),(25,'tom5',11),(26,'tom5',11),(27,'tom5',11);
40  /*!40000 ALTER TABLE `suck_t` ENABLE KEYS */;
41  UNLOCK TABLES;
42  /*!40103 SET TIME_ZONE=@OLD_TIME_ZONE */;
43  /*!40101 SET SQL_MODE=@OLD_SQL_MODE */;
44  /*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */;
45  /*!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS */;
46  /*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;
47  /*!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS */;
48  /*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */;
49  /*!40111 SET SQL_NOTES=@OLD_SQL_NOTES */;
50  -- Dump completed on 2018-12-12  1:02:27

等待空间为：

1  
2  
3  
4  
5  
6  
7  
8  
9  
10  
11  -- Dump completed on 2018-12-12  1:02:27

在'/CREATE TABLE suck_t/之后！d'，则删除模式空间中除包含CREATE TABLE suck_t的行之外的所有行。所以输出是：

27  CREATE TABLE `suck_t` (

我哪里错了？

Answer 1

这就是sed命令的作用：

# If a line is non-empty
/./ {
# Append line to hold space
H
# For every line but the last of the file, delete pattern space (print
# nothing) and start next cycle
$! d
}
# If we are here, the line was either empty or is the last line
# Swap pattern space and hold space
x
# If the pattern space does not match "CREATE TABLE `suck_t`, delete it and
# start new cycle
/CREATE TABLE `suck_t`/! d
# If we are here, the pattern space matches the "CREATE TABLE" pattern from
# above
# Print current line and quit
q

换句话说：它打印包含CREATE TABLE `suck_t`的每一个空行分隔的段落。由于输入文件只包含包含该字符串的单个段落，实际输出如下：

LOCK TABLES `suck_t` WRITE; /*!40000 ALTER TABLE `suck_t` DISABLE KEYS
*/; INSERT INTO `suck_t` VALUES (1,'tom1',11),(2,'tom2',11),(3,'tom3',11),(4,'tom4',11),(5,'tom5',11),(6,'tom5',11),(7,'tom5',11),(8,'tom5',11),(9,'tom5',11),(10,'tom5',11),(11,'tom5',11),(12,'tom5',11),(13,'tom5',11),(14,'tom5',11),(15,'tom5',11),(16,'tom5',11),(17,'tom5',11),(18,'tom5',11),(19,'tom5',11),(20,'tom5',11),(21,'tom5',11),(22,'tom5',11),(23,'tom5',11),(24,'tom5',11),(25,'tom5',11),(26,'tom5',11),(27,'tom5',11); /*!40000 ALTER TABLE `suck_t` ENABLE KEYS */; UNLOCK TABLES; /*!40103 SET TIME_ZONE=@OLD_TIME_ZONE */;

一行空白(H插入一行(和第三段从底部起的两行。

您的输出包含换行符，这些换行符既不存在于输入中，也不由sed脚本引入。

---

关于大括号的问题：它们对命令进行分组。如果我说

/./H;$!d

这意味着"对于每个匹配.的行，执行H；然后，对于每一行，删除它，除非它是最后一行"。

另一方面，

/./{H;$!d}

意思是"对于与.匹配的每一行，执行H并删除它，除非它是最后一行"。

第一个命令将删除一个空行，因为对每一行都运行$!d；第二个命令将完全跳过空行。