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<h1><a name="ApacheFelixShellService-ApacheFelixShellService"></a>Apache Felix Shell Service</h1>

<ul>
	<li><a href="#ApacheFelixShellService-overview">Overview</a></li>
	<li><a href="#ApacheFelixShellService-service">How the Shell Service Works</a></li>
	<li><a href="#ApacheFelixShellService-commands">How Commands Work</a></li>
	<li><a href="#ApacheFelixShellService-creating">Creating a Command</a></li>
	<li><a href="#ApacheFelixShellService-security">Security and the Shell Service</a></li>
	<li><a href="#ApacheFelixShellService-feedback">Feedback</a></li>
</ul>


<p><a name="ApacheFelixShellService-overview"></a></p>

<h2><a name="ApacheFelixShellService-Overview"></a>Overview</h2>

<p>In order to interact with Felix it is necessary to have some sort of
interactive shell that allows you to issue commands to the framework
and to obtain information from it. The OSGi specification does not
define how an OSGi framework should provide this interactivity. Felix
defines a shell service for creating and executing arbitrary commands.
The shell service does not define a user interface, only a service API.</p>

<p>The benefit of the Felix shell service approach is that it is possible to:</p>

<ul>
	<li>have multiple shell user interfaces (e.g., textual and graphical),</li>
	<li>add custom commands to the shell (i.e., bundles can make commands available via the shell service), and</li>
	<li>use the shell service from other bundles/services.</li>
</ul>


<p>The remainder of this document describes how the shell service works
and how to create custom commands for it. This document does not
describe how to use the command shell, nor does it describe the
text-based or GUI-based user interfaces that are available for the
shell.</p>

<p><a name="ApacheFelixShellService-service"></a></p>

<h2><a name="ApacheFelixShellService-HowtheShellServiceWorks"></a>How the Shell Service Works</h2>

<p>The Felix shell service is intended to be a simple, but extensible
shell service that can have multiple user interface implementations,
all of which are independent from the Felix framework. The shell
service is currently not intended to be sophisticated, rather it is
just a mechanism to execute commands. The shell service maintains a
list of command services, each of which have a unique command name. The
shell service is defined by the following service interface:</p>

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<div class="code">
<textarea name="newcodemacro" class="java:nocontrols:nogutter" rows="10" readonly="readonly">package org.apache.felix.shell;

public interface ShellService
{
    public String[] getCommands();
    public String getCommandUsage(String name);
    public String getCommandDescription(String name);
    public ServiceReference getCommandReference(String name);
    public void executeCommand(
        String commandLine, PrintStream out, PrintStream err)
        throws Exception;
}</textarea>
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<p>Using the shell service interface, it is possible to access and
execute available commands. The shell service methods perform the
following functions:</p>

<ul>
	<li><tt>getCommands()</tt> - returns an array of strings that correspond to the names of the installed shell commands.</li>
	<li><tt>getCommandUsage()</tt> - returns the command usage string for a particular command name</li>
	<li><tt>getCommandDescription()</tt> - returns a short description for a particular command name.</li>
	<li><tt>getCommandReference()</tt> - returns the service reference for a particular command name.</li>
	<li><tt>executeCommand()</tt> - executes a particular command using the specified command line and print streams.</li>
</ul>


<p>Most of the shell service methods require no explanation except for
the executeCommand() method. Even though this method is the most
complex, it is still fairly simplistic. The assumption of the shell
service is that a command line will be typed by the user (or perhaps
constructed by a GUI) and passed into it for execution. The shell
service interprets the command line in a very simplistic fashion; it
takes the leading string of characters terminated by a space character
(not including it) and assumes that this leading token is the command
name. Consider the following command line:</p>

<div class="preformatted panel" style="border-width: 1px;"><div class="preformattedContent panelContent">
<pre>update 3 http://www.foo.com/bar.jar
</pre>
</div></div>

<p>The shell service interprets this as an <tt>update</tt> command and
will search for a command service with the same name. If a
corresponding command service is not found, then it will print an error
message to the error print stream. If a corresponding command service
is found, then it will pass the entire command line string and the
print streams into the <tt>executeCommand()</tt> method of the command service (for a more detailed description of command services, see the next section).</p>

<p>Notice that there is no method to add commands to the shell service
interface. This is because commands are implemented as OSGi services
and the shell service listens for service events and when a command
service registers/unregisters it automatically updates its list of
commands accordingly.</p>

<p><a name="ApacheFelixShellService-commands"></a></p>

<h2><a name="ApacheFelixShellService-HowCommandsWork"></a>How Commands Work</h2>

<p>All commands available in the shell service are implemented as OSGi
services. The advantage of this approach is two-fold: the shell service
can leverage OSGi service events to maintain its list of available
commands and the set available commands is dynamically extendable by
installed bundles. The command service interface is defined as follows:</p>

<div class="code">
<textarea name="newcodemacro" class="java:nocontrols:nogutter" rows="10" readonly="readonly">package org.apache.felix.shell;

public interface Command
{
    public String getName();
    public String getUsage();
    public String getShortDescription();
    public void execute(String line, PrintStream out, PrintStream err);
}</textarea>
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<p>The semantics of the command service methods are:</p>

<ul>
	<li><tt>getName()</tt> - returns the name of the command; this must not contain whitespace and must be unique.</li>
	<li><tt>getUsage()</tt>
- returns the usage string of the command; this should be one line and
as short as possible (this is used for generating the help command
output).</li>
	<li><tt>getShortDescription()</tt> - returns a short
description of the command; this should be one line and as short as
possible (this is used for generating the help command output).</li>
	<li><tt>execute()</tt> - executes the command's functionality using supplied command line and print streams.</li>
</ul>


<p><a name="ApacheFelixShellService-creating"></a></p>

<h2><a name="ApacheFelixShellService-CreatingaCommand"></a>Creating a Command</h2>

<p>The following example creates a simple version of the <tt>start</tt> command.</p>

<div class="code">
<textarea name="newcodemacro" class="java:nocontrols:nogutter" rows="10" readonly="readonly">package test;

import java.io.PrintStream;
import java.net.URL;
import java.net.MalformedURLException;
import java.util.StringTokenizer;

import org.osgi.framework.*;
import org.apache.felix.shell.ShellService;
import org.apache.felix.shell.Command;

public class MyStartCommandImpl implements Command
{
    private BundleContext m_context = null;

    public MyStartCommandImpl(BundleContext context)
    {
        m_context = context;
    }

    public String getName()
    {
        return "mystart";
    }

    public String getUsage()
    {
        return "mystart &lt;id&gt; [&lt;id&gt; ...]";
    }

    public String getShortDescription()
    {
        return "start bundle(s).";
    }

    public void execute(String s, PrintStream out, PrintStream err)
    {
        StringTokenizer st = new StringTokenizer(s, " ");

        // Ignore the command name.
        st.nextToken();

        // There should be at least one bundle id.
        if (st.countTokens() &gt;= 1)
        {
            while (st.hasMoreTokens())
            {
                String id = st.nextToken().trim();

                try {
                    long l = Long.valueOf(id).longValue();
                    Bundle bundle = m_context.getBundle(l);
                    if (bundle != null)
                    {
                        bundle.start();
                    }
                    else
                    {
                        err.println("Bundle ID " + id + " is invalid.");
                    }
                } catch (NumberFormatException ex) {
                    err.println("Unable to parse id '" + id + "'.");
                } catch (BundleException ex) {
                    if (ex.getNestedException() != null)
                        err.println(ex.getNestedException().toString());
                    else
                        err.println(ex.toString());
                } catch (Exception ex) {
                    err.println(ex.toString());
                }
            }
        }
        else
        {
            err.println("Incorrect number of arguments");
        }
    }
}</textarea>
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<p>A bundle activator class is needed for packaging the command servce; the bundle activator registers the command service in its <tt>start()</tt> method. Note: You do not need one activator per command, a single activator can register any number of commands.</p>

<div class="code">
<textarea name="newcodemacro" class="java:nocontrols:nogutter" rows="10" readonly="readonly">package test;

import org.osgi.framework.BundleActivator;
import org.osgi.framework.BundleContext;

public class MyStartActivator implements BundleActivator
{
    private transient BundleContext m_context = null;

    public void start(BundleContext context)
    {
        m_context = context;

        // Register the command service.
        context.registerService(
            org.apache.felix.shell.Command.class.getName(),
            new MyStartCommandImpl(m_context), null);
    }

    public void stop(BundleContext context)
    {
        // Services are automatically unregistered so
        // we don't have to unregister the factory here.
    }
}</textarea>
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<p>To compile these classes you will need to have the <tt>framework.jar</tt> file on your class path. Compile all of the source files using a command like:</p>

<div class="preformatted panel" style="border-width: 1px;"><div class="preformattedContent panelContent">
<pre>java -d c:\classes *.java
</pre>
</div></div>

<p>This command compiles all of the source files and outputs the generated class files into a subdirectory of the <tt>c:\classes</tt> directory, called test, named after the package of the source files; for the above command to work, the <tt>c:\classes</tt>
directory must exist. Once you have compiled all of the above classes,
you need to create a bundle JAR file of the generated package
directory. The bundle JAR file needs a manifest, so create a file
called <tt>manifest.mf</tt> with the following contents:</p>

<div class="code">
<textarea name="newcodemacro" class="java:nocontrols:nogutter" rows="10" readonly="readonly">Bundle-Name: My Start Command
Bundle-Description: A 'start' command for the shell service.
Bundle-Activator: test.MyStartActivator
Bundle-ClassPath: .
Import-Package: org.apache.felix.shell</textarea>
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<p>To create the bundle JAR file, issue the command:</p>

<div class="preformatted panel" style="border-width: 1px;"><div class="preformattedContent panelContent">
<pre>jar cfm mystart.jar manifest.mf -C c:\classes test
</pre>
</div></div>

<p>This command creates a JAR file using the manifest you created and
includes all of the classes in the test directory inside of the <tt>c:\classes</tt>
directory. Once the bundle JAR file is created, you are ready to add
the command service to the shell service; simply start Felix and
install and start the bundle created by the above command. By doing so,
the new <tt>mystart</tt> command is made available via the shell service.</p>

<p><a name="ApacheFelixShellService-security"></a></p>

<h2><a name="ApacheFelixShellService-SecurityandtheShellService"></a>Security and the Shell Service</h2>

<p>The shell service security handling is quite simple, all security is
handled by the standard OSGi framework mechanisms. For example, if a
bundle should not be able to register a shell service, then it should
not be given the corresponding service permission. Security handling
may change in future release after some experience is gained through
usage.</p>

<p><a name="ApacheFelixShellService-feedback"></a></p>

<h2><a name="ApacheFelixShellService-Feedback"></a>Feedback</h2>

<p>Subscribe to the Felix users mailing list by sending a message to <a href="mailto:users-subscribe@felix.apache.org" rel="nofollow">users-subscribe@felix.apache.org</a>; after subscribing, email questions or feedback to <a href="mailto:users@felix.apache.org" rel="nofollow">users@felix.apache.org</a>.</p>
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