Linux CLI: Extract variable number of lines from text file based on search

Question

I have what I thought was a simple problem. I have a mysqldump file occupying several GBs, and I want to create a script that will extract just the lines of the text pertaining to one table (variable passed to the script) and save those to a new file.

The section I want to extract always starts with:

-- Table structure for table `myTable`

And always ends with:

UNLOCK TABLES;

Where the table name and the number of lines I want afterward are variable. I'm able to find the start of the section with:

START=$(grep -n "Table structure for table \`$2\`" "$1" | awk -F ":" '{print $1}')

Where $1 is the file to search and $2 is the table name. This works just fine, but then I'm stuck. I know I can extract the lines with sed once I have the ending line number, but finding that ending line number is the tricky part.

I need to find the line number of the first occurrence of UNLOCK TABLES; after my $START line number, and I'm lost on how to do that.

For more detail, here's an example of one section of text I would want to extract:

--
-- Table structure for table `myTable`
--

DROP TABLE IF EXISTS `myTable`;
/*!40101 SET @saved_cs_client     = @@character_set_client */;
/*!40101 SET character_set_client = utf8 */;
CREATE TABLE `myTable` (
  `column1` varchar(12) NOT NULL,
  `column2` varchar(20) DEFAULT NULL,
  PRIMARY KEY (`column1`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1;
/*!40101 SET character_set_client = @saved_cs_client */;

--
-- Dumping data for table `myTable`
--

LOCK TABLES `myTable` WRITE;
/*!40000 ALTER TABLE `myTable` DISABLE KEYS */;
INSERT INTO `myTable` VALUES ('test11', 'test12'),('test21', 'test22');
/*!40000 ALTER TABLE `myTable` ENABLE KEYS */;
UNLOCK TABLES;

Thanks in advance.

chepner · Accepted Answer · 2012-08-23 22:20:11Z

3

Use sed; you don't need to worry about explicit line numbers; you can just select the range using regexes for both the first and last line.

firstLine="-- Table structure for table \`$2\`"
secondLine="UNLOCK TABLES;"

sed -n "/$firstLine/,/$secondLine/p" "$1"

The -n limits sed to printing only those lines that match the desired range.

edited Aug 23, 2012 at 22:20

answered Aug 23, 2012 at 22:13

chepner

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1 Comment

Andrew Ensley Over a year ago

So this will find the first occurrence of $secondLine after $firstLine?

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