HCatalog - CLI

HCatalog Command Line Interface (CLI) can be invoked from the command $HIVE_HOME/HCatalog/bin/hcat where $HIVE_HOME is the home directory of Hive. hcat is a command used to initialize the HCatalog server.

Use the following command to initialize HCatalog command line.

cd $HCAT_HOME/bin
./hcat

If the installation has been done correctly, then you will get the following output −

SLF4J: Actual binding is of type [org.slf4j.impl.Log4jLoggerFactory]
usage: hcat { -e "<query>" | -f "<filepath>" } 
   [ -g "<group>" ] [ -p "<perms>" ] 
   [ -D"<name> = <value>" ]
	
-D <property = value>    use hadoop value for given property
-e <exec>                hcat command given from command line
-f <file>                hcat commands in file
-g <group>               group for the db/table specified in CREATE statement
-h,--help                Print help information
-p <perms>               permissions for the db/table specified in CREATE statement

The HCatalog CLI supports these command line options −

Sr.No	Option	Example & Description
1	-g	hcat -g mygroup ... The table to be created must have the group "mygroup".
2	-p	hcat -p rwxr-xr-x ... The table to be created must have read, write, and execute permissions.
3	-f	hcat -f myscript.HCatalog ... myscript.HCatalog is a script file containing DDL commands to execute.
4	-e	hcat -e 'create table mytable(a int);' ... Treat the following string as a DDL command and execute it.
5	-D	hcat -Dkey = value ... Passes the key-value pair to HCatalog as a Java system property.
6	-	hcat Prints a usage message.

Note −

The -g and -p options are not mandatory.
At one time, either -e or -f option can be provided, not both.
The order of options is immaterial; you can specify the options in any order.

Sr.No	DDL Command & Description
1	CREATE TABLE Create a table using HCatalog. If you create a table with a CLUSTERED BY clause, you will not be able to write to it with Pig or MapReduce.
2	ALTER TABLE Supported except for the REBUILD and CONCATENATE options. Its behavior remains same as in Hive.
3	DROP TABLE Supported. Behavior the same as Hive (Drop the complete table and structure).
4	CREATE/ALTER/DROP VIEW Supported. Behavior same as Hive. Note − Pig and MapReduce cannot read from or write to views.
5	SHOW TABLES Display a list of tables.
6	SHOW PARTITIONS Display a list of partitions.
7	Create/Drop Index CREATE and DROP FUNCTION operations are supported, but the created functions must still be registered in Pig and placed in CLASSPATH for MapReduce.
8	DESCRIBE Supported. Behavior same as Hive. Describe the structure.

Some of the commands from the above table are explained in subsequent chapters.