Now that we've seen how the regular expressions package works, it's time to write Grep2, a full-blown version of the line-matching program with option parsing. Table 4-3 lists some typical command-line options that a Unix implementation of grep might include.
We discussed the GetOpt class in Recipe 2.6. Here we use it to control the operation of an application program. As usual, since main( ) runs in a static context but our application main line does not, we could wind up passing a lot of information into the constructor. Because we have so many options, and it would be inconvenient to keep expanding the options list as we add new functionality to the program, we use a kind of Collection called a BitSet to pass all the true/false arguments: true to print line numbers, false to print filenames, etc. (Collections are covered in Chapter 7.) A BitSet is much like a Vector (see Recipe 7.3) but is specialized to store only Boolean values and is ideal for handling command-line arguments. The program basically just reads lines, matches the pattern in them, and, if a match is found (or not found, with -v), prints the line (and optionally some other stuff, too). Having said all that, the code is shown in Example 4-9. Example 4-9. Grep2.javaimport com.darwinsys.util.*; import java.io.*; import java.util.*; /** A command-line grep-like program. Accepts some options and takes a pattern * and a list of text files. */ public class Grep2 { /** The pattern we're looking for */ protected Matcher pattern; /** The Reader for the current file */ protected BufferedReader d; /** Are we to only count lines, instead of printing? */ protected boolean countOnly = false; /** Are we to ignore case? */ protected boolean ignoreCase = false; /** Are we to suppress printing of filenames? */ protected boolean dontPrintFileName = false; /** Are we to only list names of files that match? */ protected boolean listOnly = false; /** are we to print line numbers? */ protected boolean numbered = false; /** Are we to be silent about errors? */ protected boolean silent = false; /** are we to print only lines that DONT match? */ protected boolean inVert = false; /** Construct a Grep object for each pattern, and run it * on all input files listed in argv. */ public static void main(String[] argv) throws RESyntaxException { if (argv.length < 1) { System.err.println("Usage: Grep2 pattern [filename...]"); System.exit(1); } String pattern = null; GetOpt go = new GetOpt("cf:hilnsv"); BitSet args = new BitSet( ); char c; while ((c = go.getopt(argv)) != 0) { switch(c) { case 'c': args.set('C'); break; case 'f': try { BufferedReader b = new BufferedReader pattern = b.readLine( ); b.close( ); } catch (IOException e) { System.err.println("Can't read pattern file " + System.exit(1); } break; case 'h': args.set('H'); break; case 'i': args.set('I'); break; case 'l': args.set('L'); break; case 'n': args.set('N'); break; case 's': args.set('S'); break; case 'v': args.set('V'); break; } } int ix = go.getOptInd( ); if (pattern == null) pattern = argv[ix-1]; Grep2 pg = new Grep2(pattern, args); if (argv.length == ix) pg.process(new InputStreamReader(System.in), "(standard input)"); else for (int i=ix; i<argv.length; i++) { try { pg.process(new FileReader(argv[i]), argv[i]); } catch(Exception e) { System.err.println(e); } } } /** Construct a Grep2 object. // compile the regular expression if (args.get('C')) countOnly = true; if (args.get('H')) dontPrintFileName = true; if (args.get('I')) ignoreCase = true; if (args.get('L')) listOnly = true; if (args.get('N')) numbered = true; if (args.get('S')) silent = true; if (args.get('V')) inVert = true; int caseMode = ignoreCase ? Pattern.UNICODE_CASE | Pattern.CASE_INSENSITIVE : 0; pattern = Pattern.compile(patt, caseMode); } /** Do the work of scanning one file * @param ifile Reader Reader object already open * @param fileName String Name of the input file */ public void process(Reader ifile, String fileName) { String line; int matches = 0; try { d = new BufferedReader(ifile); while ((line = d.readLine( )) != null) { if (pattern.match(line)) { if (countOnly) matches++; else { if (!dontPrintFileName) System.out.print(fileName + ": "); System.out.println(line); } } else if (inVert) { System.out.println(line); } } if (countOnly) System.out.println(matches + " matches in " + fileName); d.close( ); } catch (IOException e) { System.err.println(e); } } } |