Ajax software     Free javascripts 
↑


Main Page

Figure A-6

These two examples have shown how you can match doubled characters using one of the syntax options

that are available. Later in this appendix, you will look at an alternative syntax that can match an exact

number of successive occurrences of a desired character, which can be exactly two or can be a larger num-

ber. The alternative syntax uses curly braces and, in addition to allowing matches of an exact number of

occurrences, allows variable numbers of occurrences to be matched.

Introducing Metacharacters

To match three characters, you can simply write the character three times in a row to form a pattern. For

example, to match part numbers that take the form

ABC123

(in other words, three alphabetic characters

followed by three numeric digits, which will match the alphabetic characters

AAA

), simply use the fol-

lowing pattern:

AAA

To match the other part of such part numbers, you need to introduce the concept of a

metacharacter

. The

patterns you have seen so far include characters that stand, literally, for the same character. A metachar-

acter can be a single character or a pair of characters (the first is typically a backslash) that has a meaning

other than the literal characters it contains.

There are several ways in which you can match the

123

part of a part number of the form

ABC123

. One

is to write the following:

\d\d\d

Each

\d

is a metacharacter that stands for a numeric digit 0 through 9, inclusive. The

\d

metacharacter

does

not

stand for a backslash followed by a lowercase

d

.

319

Appendix A: Simple Regular Expressions

bapp01.qxd:bapp01 10:47 319

Ajax software     Free javascripts 
→