|By Panos Kougiouris||
|April 1, 1999 12:00 AM EST||
Command line tools are usually invoked from a shell (e.g., DOS prompt, sh, ksh, etc.) and perform a certain task. The task can be customized based on the command line arguments. For instance:
attempts to open a telnet connection to host foo.bar.com. It uses the default telnet port. The next example:
telnet -p 3434 foo.bar.com
attempts a similar connection using port 3434.
Command line tools can be as simple or as complicated as the developer desires. An example of a simple command line tool is the echo command found in most shells. On the other hand, the Java compiler and the Java Virtual Machine (JVM) are complex command line tools.
Java presents the command line arguments in an array of strings. This is already a huge improvement over C and C++, in which the arguments are presented as an array of C strings, i.e., an array of pointers to arrays of characters. Yet it comes short of the developer's desire to get the arguments parsed and ready to use.
Since I published my 1997 C++ command line parsing framework (see Reference), many readers have e-mailed me with requests and suggestions. The top two requests have been for a Java implementation and an improvement to handle arrays of arguments. In this article I present a total rewrite of the framework with improvements for Java programmers.
Using the Framework
Before moving to the implementation I'll demonstrate how to use the framework to write a command line utility. Let's say you want to write a utility called "mycat" - like the UNIX cat - which takes a number of files and concatenates them together into a larger file. A -v option turns verbose output on and off. A -l option allows the insertion of extra empty lines between the files. The command would look like:
In your Main class you need to add a Token object for each argument. In this example we have three Tokens: the number of lines, the verbosity mode and the input files. In addition, you need to add an ApplicationSettings object. This object is used to contain all the arguments.
The source code for these settings is shown in Listing 1. I first declare the sm_main variable and then the three Token variables: sm_verbose, sm_files, sm_lines. The arguments in the constructor of each token object fully describe the expected usage of the Token:
1. Is there an environment variable to provide the value?
2. Is there a default value?
A static initializer adds the Token variables to the ApplicationSettings variable. By the time the main() function of your application is reached, the ApplicationSettings object knows everything about the syntax of your command line utility.
Listing 2 shows the main program of my example. The first line after the try statement calls the parseArgs() method of the ApplicationSettings object. The actual command line arguments are passed as an argument to the object. When the syntax is incorrect, a usage message is printed and an exception is thrown. Otherwise, the Token objects are set to contain appropriate values. For instance, when the -v option is present, the sm_verbose object will be set. Later, when its getValue() method is called, it will return true.
In a similar fashion, if two files are passed as arguments, let's say foo.cc and bar.cc, the sm_files Token will be set appropriately. Its getValue(0) method will return foo.cc, its getValue(1) method will return bar.cc.
Now compile the example with your favorite development environment and run the resulting code without passing any arguments. You should get the usage message in Listing 3. But wait a minute: you never wrote code to print usage messages; what's going on here? It's very simple. The framework uses the same code that defines the expected Tokens to generate usage statements. Kiss the ugly, always-out-of-date, static String statements that describe the usage of the utility goodbye.
Now let's run the program again with some decent arguments. Let's say we run it with arguments "-v foo.cc bar.cc". The program prints the arguments correctly. Though we didn't pass any value for the -l switch, the Token returns 0. This is the expected behavior because the default value of the sm_lines Token is indeed 0.
Why Use the Framework?
By now some of the advantages of the framework should be obvious to you. The error-prone while and switch statements that usually parse the arguments have been replaced by a few very readable statements.
1. Missing arguments
2. Unexpected arguments
3. Wrong types of arguments
The stated advantages speed up the original development of any command line utility. They allow the developer to jump to the real code as soon as possible. At the same time, they provide immediate access to the command line settings and usage messages.
Where the framework really shines is in the area where most of a developer's time is spent: software maintenance. If a command line utility is successful, users will ask for changes and improvements. Many of them will translate to more command line options or change the syntax of existing ones. The framework makes adding and modifying options trivial and safe. Compile-time messages will save the developer from runtime embarrassment.
Finally, the framework is extensible. One can define new types of switches that accommodate new data types or anything else a developer desires.
At this point you can go ahead, download the code and start using it in your own applications. The next few sections discuss the design of the framework.
The StringArrayIterator Class
The StringArrayIterator class is a utility class (see Listing 4). It encapsulates an array of strings and a position inside the array. The get() method returns the String at the current position. The moveNext() operation on the array allows the programmer to advance the current position to the next string. The EOF() operation determines when the end of the array has been reached.
The ApplicationSettings object contains a StringArrayIterator object. It gets initialized from the command line arguments.
The Token Class
The Token class, shown in Listing 5, is an abstract class. Each Token object contains a description of an argument or a switch. After a successful parsing it also contains the value or values that were provided for the argument in the command line.
During the parsing phase, the most important methods of the Token class are the parseSwitch() and parseArgument() methods. Both of them take the StringArrayIterator object with the command line arguments as input. If the current command line argument is recognized, three things occur: it's parsed, the pointer of the StringArrayIterator object is moved and a value of true is returned. If it's not recognized, a value of false is returned.
The values that correspond to this switch or argument are stored in a Vector of objects. Subclasses determine their class. For instance, the StringToken subclass will have String objects, and the IntegerToken subclass will contain Integer objects.
While the program is running, the values are accessible using the getValue(int) and getValue() operations.
A Token subclass encapsulates arguments of a specific type. For example, there's a StringToken, an IntegerToken, etc. Since most of its methods have a generic implementation, each Token subclass has very few methods to implement.
Listing 6 presents the implementation for the class StringToken. A few more subclasses are provided in the downloaded code. You can extend the framework by implementing more subclasses.
The ApplicationSettings Object
The ApplicationSettings object puts everything I've discussed so far together (see Listing 7). It contains all the Token objects and initiates the parsing algorithm. The user triggers the parsing by calling the parseArgs() method.
The command line arguments are assigned to the StringArrayIterator member of the class. Then, for every command line argument, each Token object is called and asked to parse it as either an option or an argument.
If no Token object can parse the argument, a usage message is printed by iterating through the Tokens and calling their printUsage() and printUsageExtended() methods. Both methods take an OutputStream as an argument. They print their output to this stream.
Pure Java and Impurities
Almost all the code is pure Java. Since pure Java doesn't provide support for environment variables and assertions, I had to use the functions provided in my environment, the Win32 Virtual Machine.
These few lines of code are carefully isolated in the util.java file shown in Listing 8. In a pure Java environment you can comment out three lines of code from this file. You don't get assertions and support for initialization of arguments from environment variables. Otherwise, everything else works as advertised.
The framework doesn't provide support for complex scenarios. For instance, there's no support for switches that depend on each other. You can't dictate that the -t option can appear if and only if the -p option appears. You'd have to implement such checks yourself after the arguments were parsed.
In this article I presented an extensible Java framework. The framework simplifies the development and maintenance of code that parses the arguments of command line utilities and tools.
The framework doesn't provide support for complex scenarios. Still, my experience is that the framework covers most common cases. I expect that it will be as useful for Java development as it has been for C++.
P. Kougiouris (1997). "Yet Another Command-Line Parser." C/C++ Users Journal, Vol. 15, No. 4, April.
|AST 12/04/04 10:52:06 AM EST|
Hi. Just wanted to point out another package for solving this problem. It supports popt-style autohelp as well as POSIX options, joined options (-Wall -Dfoo=bar), repeated options and of course GNU-style (--some-long-option) options.
Where the library really differs is that it leverages the GoF Command Pattern to make the options "active" in a similar manner to the Swing Action objects. Another feature is the ability to specify which sets of options must be present or cannot be present without requiring coding this logic yourself. The parser does the work for you.
An article discussing how this can be done at http://te-code.sourceforge.net/article-20041121-cli.html .
Ok, and yes, I'm a bit biased because I wrote the library... ;)
Hope this helps,
With major technology companies and startups seriously embracing IoT strategies, now is the perfect time to attend @ThingsExpo 2016 in New York and Silicon Valley. Learn what is going on, contribute to the discussions, and ensure that your enterprise is as "IoT-Ready" as it can be! Internet of @ThingsExpo, taking place Nov 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 17th Cloud Expo and will feature technical sessions from a rock star conference faculty ...
May. 26, 2016 08:15 AM EDT Reads: 2,392
Join us at Cloud Expo | @ThingsExpo 2016 – June 7-9 at the Javits Center in New York City and November 1-3 at the Santa Clara Convention Center in Santa Clara, CA – and deliver your unique message in a way that is striking and unforgettable by taking advantage of SYS-CON's unmatched high-impact, result-driven event / media packages.
May. 26, 2016 08:15 AM EDT Reads: 2,084
SYS-CON Events announced today that BMC Software has been named "Siver Sponsor" of SYS-CON's 18th Cloud Expo, which will take place on June 7-9, 2015 at the Javits Center in New York, New York. BMC is a global leader in innovative software solutions that help businesses transform into digital enterprises for the ultimate competitive advantage. BMC Digital Enterprise Management is a set of innovative IT solutions designed to make digital business fast, seamless, and optimized from mainframe to mo...
May. 26, 2016 08:00 AM EDT Reads: 1,926
18th Cloud Expo, taking place June 7-9, 2016, at the Javits Center in New York City, NY, will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud strategy. Meanwhile, 94% of enterprises are using some...
May. 26, 2016 07:45 AM EDT Reads: 2,906
SoftLayer operates a global cloud infrastructure platform built for Internet scale. With a global footprint of data centers and network points of presence, SoftLayer provides infrastructure as a service to leading-edge customers ranging from Web startups to global enterprises. SoftLayer's modular architecture, full-featured API, and sophisticated automation provide unparalleled performance and control. Its flexible unified platform seamlessly spans physical and virtual devices linked via a world...
May. 26, 2016 07:45 AM EDT Reads: 1,852
The IoTs will challenge the status quo of how IT and development organizations operate. Or will it? Certainly the fog layer of IoT requires special insights about data ontology, security and transactional integrity. But the developmental challenges are the same: People, Process and Platform. In his session at @ThingsExpo, Craig Sproule, CEO of Metavine, will demonstrate how to move beyond today's coding paradigm and share the must-have mindsets for removing complexity from the development proc...
May. 26, 2016 07:45 AM EDT Reads: 1,831
In his keynote at 18th Cloud Expo, Andrew Keys, Co-Founder of ConsenSys Enterprise, will provide an overview of the evolution of the Internet and the Database and the future of their combination – the Blockchain. Andrew Keys is Co-Founder of ConsenSys Enterprise. He comes to ConsenSys Enterprise with capital markets, technology and entrepreneurial experience. Previously, he worked for UBS investment bank in equities analysis. Later, he was responsible for the creation and distribution of life ...
May. 26, 2016 07:30 AM EDT Reads: 1,815
SYS-CON Events announced today that Tintri Inc., a leading producer of VM-aware storage (VAS) for virtualization and cloud environments, will exhibit at the 18th International CloudExpo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, New York, and the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA.
May. 26, 2016 07:15 AM EDT Reads: 2,150
Designing IoT applications is complex, but deploying them in a scalable fashion is even more complex. A scalable, API first IaaS cloud is a good start, but in order to understand the various components specific to deploying IoT applications, one needs to understand the architecture of these applications and figure out how to scale these components independently. In his session at @ThingsExpo, Nara Rajagopalan is CEO of Accelerite, will discuss the fundamental architecture of IoT applications, ...
May. 26, 2016 06:45 AM EDT Reads: 1,023
The IoT is changing the way enterprises conduct business. In his session at @ThingsExpo, Eric Hoffman, Vice President at EastBanc Technologies, discuss how businesses can gain an edge over competitors by empowering consumers to take control through IoT. We'll cite examples such as a Washington, D.C.-based sports club that leveraged IoT and the cloud to develop a comprehensive booking system. He'll also highlight how IoT can revitalize and restore outdated business models, making them profitable...
May. 26, 2016 06:30 AM EDT Reads: 2,658
SYS-CON Events announced today that Commvault, a global leader in enterprise data protection and information management, has been named “Bronze Sponsor” of SYS-CON's 18th International Cloud Expo, which will take place on June 7–9, 2016, at the Javits Center in New York City, NY, and the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Commvault is a leading provider of data protection and information management...
May. 26, 2016 06:30 AM EDT Reads: 2,832
SYS-CON Events announced today Object Management Group® has been named “Media Sponsor” of SYS-CON's 18th International Cloud Expo, which will take place on June 7–9, 2016, at the Javits Center in New York City, NY, and the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA.
May. 26, 2016 06:15 AM EDT Reads: 2,283
Companies can harness IoT and predictive analytics to sustain business continuity; predict and manage site performance during emergencies; minimize expensive reactive maintenance; and forecast equipment and maintenance budgets and expenditures. Providing cost-effective, uninterrupted service is challenging, particularly for organizations with geographically dispersed operations.
May. 26, 2016 06:15 AM EDT Reads: 1,702
SYS-CON Events announced today that Alert Logic, Inc., the leading provider of Security-as-a-Service solutions for the cloud, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. Alert Logic, Inc., provides Security-as-a-Service for on-premises, cloud, and hybrid infrastructures, delivering deep security insight and continuous protection for customers at a lower cost than traditional security solutions. Ful...
May. 26, 2016 05:45 AM EDT Reads: 2,649
SYS-CON Events announced today that MobiDev will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. MobiDev is a software company that develops and delivers turn-key mobile apps, websites, web services, and complex software systems for startups and enterprises. Since 2009 it has grown from a small group of passionate engineers and business managers to a full-scale mobile software company with over 200 develope...
May. 26, 2016 05:15 AM EDT Reads: 2,416
WebRTC is bringing significant change to the communications landscape that will bridge the worlds of web and telephony, making the Internet the new standard for communications. Cloud9 took the road less traveled and used WebRTC to create a downloadable enterprise-grade communications platform that is changing the communication dynamic in the financial sector. In his session at @ThingsExpo, Leo Papadopoulos, CTO of Cloud9, will discuss the importance of WebRTC and how it enables companies to fo...
May. 26, 2016 05:00 AM EDT Reads: 2,464
SYS-CON Events announced today that EastBanc Technologies will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. EastBanc Technologies has been working at the frontier of technology since 1999. Today, the firm provides full-lifecycle software development delivering flexible technology solutions that seamlessly integrate with existing systems – whether on premise or cloud. EastBanc Technologies partners with p...
May. 26, 2016 05:00 AM EDT Reads: 1,995
SYS-CON Events announced today TechTarget has been named “Media Sponsor” of SYS-CON's 18th International Cloud Expo, which will take place on June 7–9, 2016, at the Javits Center in New York City, NY, and the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. TechTarget is the Web’s leading destination for serious technology buyers researching and making enterprise technology decisions. Its extensive global networ...
May. 26, 2016 04:30 AM EDT Reads: 3,086
SYS-CON Events announced today BZ Media LLC has been named “Media Sponsor” of SYS-CON's 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. BZ Media LLC is a high-tech media company that produces technical conferences and expositions, and publishes a magazine, newsletters and websites in the software development, SharePoint, mobile development and Commercial Drone markets.
May. 26, 2016 03:00 AM EDT Reads: 3,457
SYS-CON Events announced today that MangoApps will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. MangoApps provides modern company intranets and team collaboration software, allowing workers to stay connected and productive from anywhere in the world and from any device. For more information, please visit https://www.mangoapps.com/.
May. 26, 2016 12:45 AM EDT Reads: 593