HCatalog CLI

CLI is abbreviated as command line interface (CLI). The HCatalog command line interface (CLI) can be invoked as HCATALOG_HOME= hcat_home/bin/hcat. hcat_home is the directory where HCatalog has been installed. User can also invoke the CLI by doing /usr/bin/hcat.

The HCatalog CLI supports these command line options −

Option	Usage / Example	Description
	hcat	Prints usage messages.
-g	hcat -g group-name ...	The table that needs to be created must have group "group-name".
-p	hcat -p rwxr-xr-x ...	The table that needs to be created must have permissions "rwxr-xr-x".
-f	hcat -f userscript.hcatalog ...	Specifies userscript.hcatalog is a file containing DDL commands to execute.
-e	hcat -e 'create table usertable(a int);' ...	Specifies HCatalog to treat the specified string as a DDL command and execute it.
-D	hcat -Dkey=value ...	Passes the key-value pair to HCatalog as a Java System Property.

• The -g and -p options are optional.
• Either -e or -f option can be provided, but not both.
• The orders of options are not important and can specify the options in any order.

If no option is provided, the usage message will appear as follows: -

Usage:  hcat  { -e "<query>" |
 -f <filepath> }  [-g <group>] 
 [-p <perms>] [-D<name>=<value>]

The HCatalog CLI includes some commands which are not available in the HCatalog CLI. "hcat -g" and "hcat -p" for table group and permission settings are only available in the HCatalog CLI.

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

To get help, run "hive -H" or "hive --help" -

usage: hive
 -d,--define <key=value>          Variable substitution to apply to Hive
                                  commands. e.g. -d A=B or --define A=B
 -e <quoted-query-string>         SQL from command line
 -f <filename>                    SQL from files
 -H,--help                        Print help information
 -h <hostname>                    Connecting to Hive Server on remote host
    --hiveconf <property=value>   Use value for given property
    --hivevar <key=value>         Variable substitution to apply to hive
                                  commands. e.g. --hivevar A=B
 -i <filename>                    Initialization SQL file
 -p <port>                        Connecting to Hive Server on port number
 -S,--silent                      Silent mode in interactive shell
 -v,--verbose                     Verbose mode (echo executed SQL to the
                                  console)

Many of hcat commands can be used as HCatalog commands which include all HCatalog DDL commands.

DDL Command	Description
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.
ALTER TABLE	Supported except for the REBUILD and CONCATENATE options. Its behavior remains same as in Hive.
DROP TABLE	Supported. Behavior the same as Hive (Drop the complete table and structure).
CREATE/ALTER/DROP VIEW	Supported. Behavior same as Hive.
SHOW TABLES	Display a list of tables.
SHOW PARTITIONS	Display a list of partitions.
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.
DESCRIBE	Supported. Behavior same as Hive. Describe the structure.

---