Interacting with the Environment - Java - page 72

Solution

Look in the args array passed as an argument to main . Or use my GetOpt class.

Discussion

The Unix folks have had to deal with this longer than anybody, and they came up with a C-
library function called getopt . [ 11 ] getopt processes your command-line arguments and
looks for single-character options set off with dashes and optional arguments. For example,
the command:

sort -n -o outfile myfile1 yourfile2

runs the Unix/Linux/Mac system-provided sort program. The -n tells it that the records are
numeric rather than textual, and the -o outfile tells it to write its output into a file named
outfile . The remaining words, myfile1 and yourfile2 , are treated as the input files to be sorted.
On Windows, command arguments are sometimes set off with slashes ( / ). We use the Unix
form—a dash—in our API, but feel free to change the code to use slashes.

Each GetOpt parser instance is constructed to recognize a particular set of arguments, be-
cause a given program normally has a fixed set of arguments that it accepts. You can con-
struct an array of GetOptDesc objects that represent the allowable arguments. For the sort
program shown previously, you might use:

GetOptDesc [] options = {
new

new GetOptDesc ( 'n' , "numeric" , false false ),

new new GetOptDesc ( 'o' , "output-file" , true true ),

};
Map optionsFound = new

new GetOpt ( options ). parseArguments ( argv );
iif ( optionsFound . get ( "n" ) != null null ) {

System . out . println ( "sortType = NUMERIC;" )

}
String outputFile = null null ;

iif (( outputFile = optionsFound . get ( "o" ) != null

null ) {
System . out . println ( "output file specified as " + outputFile )
} else else {

System . out . println ( "Output to System.out" );

}

The simple way of using GetOpt is to call its parseArguments method.