The "getopt4j" library is designed to parse the command line options in the same manner as the C getopt() function in glibc (the GNU C runtime library). It attempts to do this in a simpler, more Java-centric manner than the original product.
The easiest way to download the library is to add the maven dependency;
<dependency>
<groupId>org.realityforge.getopt4j</groupId>
<artifactId>getopt4j</artifactId>
<version>1.3</version>
</dependency>The best way to understand how the library works is to dive into the examples in the examples directory. However if you want to understand more about how the parser works read on.
The command line is parsed according to the following rules. There are two forms of options in this package, the long form and the short form. The long form of an option is preceded by the '--' characters while the short form is preceded by a single '-'. Some example options would be; "--an-option", "-a", "--day", "-s -f -a".
In the tradition of UNIX programs, the short form of an option can occur immediately after another short form option. So if 'a', 'b' and 'c' are short forms of options that take no parameters then the following command lines are equivalent: "-abc", "-a -bc", "-a -b -c", "-ab -c", etc.
Options can also accept arguments. You can specify that an option requires an argument in which the text immediately following the option will be considered to be an argument to the option. So if 'a' was an option that required an argument then the following would be equivalent; "-abc", "-a bc" (namely the option 'a' with argument 'bc').
Options can also specify optional arguments. In this case if there is any text immediately following the option character then it is considered an argument. Otherwise, the option has no arguments. For example if 'a' was an option that required an optional argument then "-abc" is an option 'a' with argument "bc" while "-a bc" is an option 'a' with no argument, followed by the text "bc".
It is also possible to place an '=' sign between the option and it's argument. So if we assume that a is an option that requires an argument then the following are all equivalent; "-a=bc", "-a bc" "-abc".
In some cases it is also necessary to disable command line parsing so that you can pass a text argument to the program that starts with a '-' character. To do this insert the sequence '--' onto the command line with no text immediately following it. This will disable processing for the rest of the command line. The '--' characters will not be passed to the user program. For instance the line "-- -b" would result in the program being passed the text "-b" (ie. not as an option).
The code originates from a small project written in 1998 and has remained largely unchanged. However it has done several stints at some open-source organizations and thus it needs to state "This product includes software developed by the Apache Software Foundation (http://www.apache.org/)." Thanks also goes out to Jeff Turner who added some documentation and Berin Loritsch who fixed a parser bug that got through.