Java Cookbook

Program: Full Grep

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.

Table 4-3. Grep command-line options

Option	Meaning
-c	Count only: don’t print lines, just count them
-f pattern	Take pattern from file named after -f instead of from command line
-h	Suppress printing filename ahead of lines
-i	Ignore case
-l	List filenames only: don’t print lines, just the names they’re found in
-n	Print line numbers before matching lines
-s	Suppress printing certain error messages
-v	Invert: print only lines that do NOT match the pattern

We discussed the GetOpt class back in Section 2.8. 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 Section 7.4) but is specialized to store only boolean values, and is ideal for handling command-line ...