Here in this chapter, we will see how how to run Apache Pig scripts in batch mode.
While writing a script in a file, we can include comments in it as shown below.
We will begin the multi-line comments with '/*', end them with '*/'.
/* These are the multi-line comments In the pig script */
We will begin the single-line comments with '--'.
--we can write single line comments like this.
While executing Apache Pig statements in batch mode, follow the steps given below.
Write all the required Pig Latin statements in a single file. We can write all the Pig Latin statements and commands in a single file and save it as .pig file.
Execute the Apache Pig script. You can execute the Pig script from the shell (Linux) as shown below.
|Local mode||MapReduce mode|
|$ pig -x local Sample_script.pig||$ pig -x mapreduce Sample_script.pig|
You can execute it from the Grunt shell as well using the exec command as shown below.
grunt> exec /sample_script.pig
We can also execute a Pig script that resides in the HDFS. Suppose there is a Pig script with the name Sample_script.pig in the HDFS directory named /pig_data/. We can execute it as shown below.
$ pig -x mapreduce hdfs://localhost:9000/pig_data/Sample_script.pig
Assume we have a file student_details.txt in HDFS with the following content.
001,Rajiv,Reddy,21,9848022337,Hyderabad 002,siddarth,Battacharya,22,9848022338,Kolkata 003,Rajesh,Khanna,22,9848022339,Delhi 004,Preethi,Agarwal,21,9848022330,Pune 005,Trupthi,Mohanthy,23,9848022336,Bhuwaneshwar 006,Archana,Mishra,23,9848022335,Chennai 007,Komal,Nayak,24,9848022334,trivendram 008,Bharathi,Nambiayar,24,9848022333,Chennai
We also have a sample script with the name sample_script.pig, in the same HDFS directory. This file contains statements performing operations and transformations on the student relation, as shown below.
student = LOAD 'hdfs://localhost:9000/pig_data/student_details.txt' USING PigStorage(',') as (id:int, firstname:chararray, lastname:chararray, phone:chararray, city:chararray); student_order = ORDER student BY age DESC; student_limit = LIMIT student_order 4; Dump student_limit;
The first statement of the script will load the data in the file named student_details.txt as a relation named student.
The second statement of the script will arrange the tuples of the relation in descending order, based on age, and store it as student_order.
The third statement of the script will store the first 4 tuples of student_order as student_limit.
Finally the fourth statement will dump the content of the relation student_limit.
Let us now execute the sample_script.pig as shown below.
$./pig -x mapreduce hdfs://localhost:9000/pig_data/sample_script.pig
Apache Pig gets executed and gives you the output with the following content.
(7,Komal,Nayak,24,9848022334,trivendram) (8,Bharathi,Nambiayar,24,9848022333,Chennai) (5,Trupthi,Mohanthy,23,9848022336,Bhuwaneshwar) (6,Archana,Mishra,23,9848022335,Chennai) 2015-10-19 10:31:27,446 [main] INFO org.apache.pig.Main - Pig script completed in 12 minutes, 32 seconds and 751 milliseconds (752751 ms)