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<?xml version="1.0"?>
<!--
Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements. See the NOTICE file
distributed with this work for additional information
regarding copyright ownership. The ASF licenses this file
to you under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance
with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing,
software distributed under the License is distributed on an
"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
KIND, either express or implied. See the License for the
specific language governing permissions and limitations
under the License.
-->
<document>
<properties>
<author email="commons-dev@jakarta.apache.org">commons-dev</author>
<title>Usage Scenarios</title>
</properties>
<body>
<section name="Usage Scenarios">
<p>
The following sections describe some example scenarios on how to
use CLI in applications.
</p>
<subsection name="Using a boolean option">
<p>
A boolean option is represented on a command line by the presence
of the option, i.e. if the option is found then the option value
is <code>true</code>, otherwise the value is <code>false</code>.
</p>
<p>
The <code>DateApp</code> utility prints the current date to standard
output. If the <code>-t</code> option is present the current time is
also printed.
</p>
</subsection>
<subsection name="Create the Options">
<p>
An <a href="apidocs/org/apache/commons/cli/Options.html">
Options</a> object must be created and the <code>Option</code> must be
added to it.
</p>
<source>
// create Options object
Options options = new Options();
// add t option
options.addOption("t", false, "display current time");</source>
<p>
The <code>addOption</code> method has three parameters. The first
parameter is a <code>java.lang.String</code> that represents the option.
The second parameter is a <code>boolean</code> that specifies whether the
option requires an argument or not. In the case of a boolean option
(sometimes referred to as a flag) an argument value is not present so
<code>false</code> is passed. The third parameter is the description
of the option. This description will be used in the usage text of the
application.
</p>
</subsection>
<subsection name="Parsing the command line arguments">
<p>
The <code>parse</code> methods of <code>CommandLineParser</code> are used
to parse the command line arguments. The <code>PosixPaser</code> is
great when you need to handle options that are one character long,
like the <code>t</code> option in this example.
</p>
<source>CommandLineParser parser = new PosixParser();
CommandLine cmd = parser.parse( options, args);</source>
<p>
Now we need to check if the <code>t</code> option is present. To do
this we will interrogate the
<a href="apidocs/org/apache/commons/cli/CommandLine.html">CommandLine
</a> object. The <code>hasOption</code> method takes a
<code>java.lang.String</code> parameter and returns <code>true</code> if the option
represented by the <code>java.lang.String</code> is present, otherwise
it returns <code>false</code>.
</p>
<source>if(cmd.hasOption("t")) {
// print the date and time
}
else {
// print the date
}</source>
</subsection>
<subsection name="International Time">
<p>
The <code>InternationalDateApp</code> utility extends the
<code>DateApp</code> utility by providing the ability to print the
date and time in any country in the world. To facilitate this a new
command line option, <code>c</code>, has been introduced.
</p>
<source>// add c option
options.addOption("c", true, "country code");</source>
<p>
The second parameter is <code>true</code> this time. This specifies that the
<code>c</code> option requires an argument value. If the required option
argument value is specified on the command line it is returned,
otherwise <code>null</code> is returned.
</p>
</subsection>
<subsection name="Retrieving the argument value">
<p>
The <code>getOptionValue</code> methods of <code>CommandLine</code> are
used to retrieve the argument values of options.
</p>
<source>// get c option value
String countryCode = cmd.getOptionValue("c");
if(countryCode == null) {
// print default date
}
else {
// print date for country specified by countryCode
}</source>
</subsection>
</section>
<section name="Ant Example">
<p>
One of the most ubiquitous Java applications
<a href="http://ant.apache.org/">Ant</a> will be used
here to illustrate how to create the <code>Options</code> required. The following
is the help output for Ant.
</p>
<source>ant [options] [target [target2 [target3] ...]]
Options:
-help print this message
-projecthelp print project help information
-version print the version information and exit
-quiet be extra quiet
-verbose be extra verbose
-debug print debugging information
-emacs produce logging information without adornments
-logfile <file> use given file for log
-logger <classname> the class which is to perform logging
-listener <classname> add an instance of class as a project listener
-buildfile <file> use given buildfile
-D<property>=<value> use value for given property
-find <file> search for buildfile towards the root of the
filesystem and use it</source>
<subsection name="Boolean Options">
<p>
Lets create the boolean options for the application as they
are the easiest to create. For clarity the constructors for
<code>Option</code> are used here.
</p>
<source>Option help = new Option( "help", "print this message" );
Option projecthelp = new Option( "projecthelp", "print project help information" );
Option version = new Option( "version", "print the version information and exit" );
Option quiet = new Option( "quiet", "be extra quiet" );
Option verbose = new Option( "verbose", "be extra verbose" );
Option debug = new Option( "debug", "print debugging information" );
Option emacs = new Option( "emacs",
"produce logging information without adornments" );</source>
</subsection>
<subsection name="Argument Options">
<p>
The argument options are created using the <code>OptionBuilder</code>.
</p>
<source>Option logfile = OptionBuilder.withArgName( "file" )
.hasArg()
.withDescription( "use given file for log" )
.create( "logfile" );
Option logger = OptionBuilder.withArgName( "classname" )
.hasArg()
.withDescription( "the class which it to perform "
+ "logging" )
.create( "logger" );
Option l
FAFF
istener = OptionBuilder.withArgName( "classname" )
.hasArg()
.withDescription( "add an instance of class as "
+ "a project listener" )
.create( "listener");
Option buildfile = OptionBuilder.withArgName( "file" )
.hasArg()
.withDescription( "use given buildfile" )
.create( "buildfile");
Option find = OptionBuilder.withArgName( "file" )
.hasArg()
.withDescription( "search for buildfile towards the "
+ "root of the filesystem and use it" )
.create( "find" );</source>
</subsection>
<subsection name="Java Property Option">
<p>
The last option to create is the Java property and it is also created
using the OptionBuilder.
</p>
<source>Option property = OptionBuilder.withArgName( "property=value" )
.hasArg()
.withValueSeparator()
.withDescription( "use value for given property" )
.create( "D" );</source>
</subsection>
<subsection name="Create the Options">
<p>
Now that we have created each
<a href="apidocs/org/apache/commons/cli/Option.html">Option</a> we need
to create the
<a href="apidocs/org/apache/commons/cli/Options.html">Options</a>
instance. This is achieved using the
<a href="apidocs/org/apache/commons/cli/CommandLine.html#addOption(org.apache.commons.cli.Option)">addOption</a>
method of <code>Options</code>.
</p>
<source>Options options = new Options();
options.addOption( help );
options.addOption( projecthelp );
options.addOption( version );
options.addOption( quiet );
options.addOption( verbose );
options.addOption( debug );
options.addOption( emacs );
options.addOption( logfile );
options.addOption( logger );
options.addOption( listener );
options.addOption( buildfile );
options.addOption( find );
options.addOption( property );</source>
<p>
All the preperation is now complete and we are now ready to
parse the command line arguments.
</p>
</subsection>
<subsection name="Create the Parser">
<p>
We now need to create a <code>Parser</code>. This will parse the command
line arguments, using the rules specified by the <code>Options</code> and
return an instance of <a href="apidocs/org/apache/commons/cli/CommandLine.html">CommandLine</a>.
This time we will use a <a href="apidocs/org/apache/commons/cli/GnuParser.html">GnuParser</a>
which is able to handle options that are more than one character long.
</p>
<source>public static void main( String[] args ) {
// create the parser
CommandLineParser parser = new GnuParser();
try {
// parse the command line arguments
CommandLine line = parser.parse( options, args );
}
catch( ParseException exp ) {
// oops, something went wrong
System.err.println( "Parsing failed. Reason: " + exp.getMessage() );
}
}</source>
</subsection>
<subsection name="Querying the commandline">
<p>
To see if an option has been passed the <code>hasOption</code>
method is used. The argument value can be retrieved using
the <code>getValue</code> method.
</p>
<source>// has the buildfile argument been passed?
if( line.hasOption( "buildfile" ) ) {
// initialise the member variable
this.buildfile = line.getValue( "buildfile" );
}</source>
</subsection>
<subsection name="Usage/Help">
<p>
CLI also provides the means to automatically generate usage
and help information. This is achieved with the
<a href="apidocs/org/apache/commons/cli/HelpFormatter.html">HelpFormatter</a>
class.
</p>
<source>// automatically generate the help statement
HelpFormatter formatter = new HelpFormatter();
formatter.printHelp( "ant", options );</source>
<p>
When executed the following output is produced:
</p>
<source>usage: ant
-D <property=value> use value for given property
-buildfile <file> use given buildfile
-debug print debugging information
-emacs produce logging information without adornments
-file <file> search for buildfile towards the root of the
filesystem and use it
-help print this message
-listener <classname> add an instance of class as a project listener
-logger <classname> the class which it to perform logging
-projecthelp print project help information
-quiet be extra quiet
-verbose be extra verbose
-version print the version information and exit</source>
<p>
If you also require to have a usage statement printed
then calling <code>formatter.printHelp( "ant", options, true )</code>
will generate a usage statment as well as the help information.
</p>
</subsection>
</section>
<section name="ls Example">
<p>
One of the most widely used command line applications in the *nix world
is <code>ls</code>. To parse a command line for an application like this
we will use the <a href="apidocs/org/apache/commons/cli/PosixParser.html">PosixParser</a>.
Due to the large number of options required for <code>ls</code> this
example will only cover a small proportion of the options. The following
is a section of the help output.
</p>
<source>Usage: ls [OPTION]... [FILE]...
List information about the FILEs (the current directory by default).
Sort entries alphabetically if none of -cftuSUX nor --sort.
-a, --all do not hide entries starting with .
-A, --almost-all do not list implied . and ..
-b, --escape print octal escapes for nongraphic characters
--block-size=SIZE use SIZE-byte blocks
-B, --ignore-backups do not list implied entries ending with ~
-c with -lt: sort by, and show, ctime (time of last
modification of file status information)
with -l: show ctime and sort by name
otherwise: sort by ctime
-C list entries by columns</source>
<p>
The following is the code that is used to create the
<a href="apidocs/org/apache/commons/cli/Options.html">Options</a> for this example.
</p>
<source>// create the command line parser
CommandLineParser parser = new PosixParser();
// create the Options
Options options = new Options();
options.addOption( "a", "all", false, "do not hide entries starting with ." );
options.addOption( "A", "almost-all", false, "do not list implied . and .." );
options.addOption( "b", "escape", false, "print octal escapes for nongraphic "
+ "characters" );
options.addOption( OptionBuilder.withLongOpt( "block-size" )
.withDescription( "use SIZE-byte blocks" )
.withValueSeparator( '=' )
.hasArg()
.create() );
options.addOption( "B", "ignore-backups", false, "do not list implied entried "
+ "ending with ~");
options.addOption( "c", false, "with -lt: sort by, and show, ctime (time of last "
+ "modification of file status information) with "
+ "-l:show ctime and sort by name otherwise: sort "
+ "by ctime" );
options.addOption( "C", false, "list entries by columns" );
String[] args = new String[]{ "--block-size=10" };
try {
// parse the command line arguments
CommandLine line = parser.parse( options, args );
// validate that block-size has been set
if( line.hasOption( "block-size" ) ) {
// print the value of block-size
System.out.println( line.getOptionValue( "block-size" ) );
}
}
catch( ParseException exp ) {
System.out.println( "Unexpected exception:" + exp.getMessage() );
}</source>
</section>
</body>
</document>