HBASE-11655 Document how to use Bash with HBase Shell (Misty Stanley-Jones)
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Jonathan M Hsieh
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<section
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xml:id="scripting">
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<title>Scripting</title>
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<title>Scripting with Ruby</title>
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<para>For examples scripting Apache HBase, look in the HBase <filename>bin</filename>
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directory. Look at the files that end in <filename>*.rb</filename>. To run one of these
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files, do as follows:</para>
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<programlisting>$ ./bin/hbase org.jruby.Main PATH_TO_SCRIPT</programlisting>
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</section>
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<section>
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<title>Running the Shell in Non-Interactive Mode</title>
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<para>A new non-interactive mode has been added to the HBase Shell (<link
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xlink:href="https://issues.apache.org/jira/browse/HBASE-11658">HBASE-11658)</link>.
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Non-interactive mode captures the exit status (success or failure) of HBase Shell
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commands and passes that status back to the command interpreter. If you use the normal
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interactive mode, the HBase Shell will only ever return its own exit status, which will
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nearly always be <literal>0</literal> for success.</para>
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<para>To invoke non-interactive mode, pass the <option>-n</option> or
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<option>--non-interactive</option> option to HBase Shell.</para>
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</section>
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<section xml:id="hbase.shell.noninteractive">
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<title>HBase Shell in OS Scripts</title>
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<para>You can use the HBase shell from within operating system script interpreters like the
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Bash shell which is the default command interpreter for most Linux and UNIX
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distributions. The following guidelines use Bash syntax, but could be adjusted to work
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with C-style shells such as csh or tcsh, and could probably be modified to work with the
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Microsoft Windows script interpreter as well. Submissions are welcome.</para>
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<note>
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<para>Spawning HBase Shell commands in this way is slow, so keep that in mind when you
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are deciding when combining HBase operations with the operating system command line
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is appropriate.</para>
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</note>
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<example>
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<title>Passing Commands to the HBase Shell</title>
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<para>You can pass commands to the HBase Shell in non-interactive mode (see <xref
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linkend="hbasee.shell.noninteractive"/>) using the <command>echo</command>
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command and the <literal>|</literal> (pipe) operator. Be sure to escape characters
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in the HBase commands which would otherwise be interpreted by the shell. Some
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debug-level output has been truncated from the example below.</para>
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<screen>$ <userinput>echo "describe 'test1'" | ./hbase shell -n</userinput>
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<computeroutput>
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Version 0.98.3-hadoop2, rd5e65a9144e315bb0a964e7730871af32f5018d5, Sat May 31 19:56:09 PDT 2014
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describe 'test1'
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DESCRIPTION ENABLED
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'test1', {NAME => 'cf', DATA_BLOCK_ENCODING => 'NON true
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E', BLOOMFILTER => 'ROW', REPLICATION_SCOPE => '0',
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VERSIONS => '1', COMPRESSION => 'NONE', MIN_VERSIO
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NS => '0', TTL => 'FOREVER', KEEP_DELETED_CELLS =>
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'false', BLOCKSIZE => '65536', IN_MEMORY => 'false'
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, BLOCKCACHE => 'true'}
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1 row(s) in 3.2410 seconds
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</computeroutput>
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</screen>
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<para>To suppress all output, echo it to <filename>/dev/null:</filename></para>
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<screen>$ <userinput>echo "describe 'test'" | ./hbase shell -n > /dev/null 2>&1</userinput></screen>
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</example>
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<example>
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<title>Checking the Result of a Scripted Command</title>
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<para>Since scripts are not designed to be run interactively, you need a way to check
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whether your command failed or succeeded. The HBase shell uses the standard
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convention of returning a value of <literal>0</literal> for successful commands, and
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some non-zero value for failed commands. Bash stores a command's return value in a
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special environment variable called <varname>$?</varname>. Because that variable is
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overwritten each time the shell runs any command, you should store the result in a
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different, script-defined variable.</para>
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<para>This is a naive script that shows one way to store the return value and make a
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decision based upon it.</para>
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<programlisting language="bourne">
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#!/bin/bash
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echo "describe 'test'" | ./hbase shell -n > /dev/null 2>&1
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status=$?
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echo "The status was " $status
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if ($status == 0); then
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echo "The command succeeded"
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else
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echo "The command may have failed."
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fi
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return $status
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</programlisting>
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</example>
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<section>
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<title>Checking for Success or Failure In Scripts</title>
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<para>Getting an exit code of 0 means that the command you scripted definitely
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succeeded. However, getting a non-zero exit code does not necessarily mean the
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command failed. The command could have succeeded, but the client lost connectivity,
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or some other event obscured its succewss. This is because RPC commands are
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stateless. The only way to be sure of the status of an operation is to check. For
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instance, if your script creates a table, but returns a non-zero exit value, you
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should check whether the table was actually created before trying again to create
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it.</para>
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</section>
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</section>
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<section>
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<title>Read HBase Shell Commands from a Command File</title>
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<para>You can enter HBase Shell commands into a text file, one command per line, and pass
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that file to the HBase Shell.</para>
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<example>
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<title>Example Command File</title>
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<screen>
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create 'test', 'cf'
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list 'test'
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put 'test', 'row1', 'cf:a', 'value1'
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put 'test', 'row2', 'cf:b', 'value2'
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put 'test', 'row3', 'cf:c', 'value3'
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put 'test', 'row4', 'cf:d', 'value4'
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scan 'test'
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get 'test', 'row1'
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disable 'test'
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enable 'test'
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</screen>
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</example>
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<example>
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<title>Directing HBase Shell to Execute the Commands</title>
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<para>Pass the path to the command file as the only argument to the <command>hbase
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shell</command> command. Each command is executed and its output is shown. If
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you do not include the <command>exit</command> command in your script, you are
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returned to the HBase shell prompt. There is no way to programmatically check each
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individual command for success or failure. Also, though you see the output for each
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command, the commands themselves are not echoed to the screen so it can be difficult
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to line up the command with its output.</para>
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<screen>
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$ <userinput>./hbase shell ./sample_commands.txt</userinput>
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<computeroutput>0 row(s) in 3.4170 seconds
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TABLE
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test
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1 row(s) in 0.0590 seconds
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0 row(s) in 0.1540 seconds
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0 row(s) in 0.0080 seconds
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0 row(s) in 0.0060 seconds
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0 row(s) in 0.0060 seconds
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ROW COLUMN+CELL
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row1 column=cf:a, timestamp=1407130286968, value=value1
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row2 column=cf:b, timestamp=1407130286997, value=value2
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row3 column=cf:c, timestamp=1407130287007, value=value3
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row4 column=cf:d, timestamp=1407130287015, value=value4
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4 row(s) in 0.0420 seconds
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COLUMN CELL
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cf:a timestamp=1407130286968, value=value1
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1 row(s) in 0.0110 seconds
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0 row(s) in 1.5630 seconds
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0 row(s) in 0.4360 seconds</computeroutput>
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</screen>
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</example>
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</section>
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<section>
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<title>Passing VM Options to the Shell</title>
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<para>You can pass VM options to the HBase Shell using the <code>HBASE_SHELL_OPTS</code>
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