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Figure A-18

As you can see, the only change from the result of using the pattern

ABC[0-9]*

is that the pattern

ABC[0-9]+

fails to match the part number

ABC

.

When the regular expression engine is at the position immediately before the uppercase

A

of the part

number

ABC

, it attempts to match an uppercase

A

. That matches. Next, subsequent attempts are made

to match an uppercase

B

and an uppercase

C

. They too match. At that stage, the first three characters

in the regular expression pattern have been matched. Finally, an attempt is made to match the pattern

[0-9]+

, which means “Match one or more numeric characters.” There are zero numeric digits follow-

ing the uppercase

C

. Because there are exactly zero numeric digits after the uppercase

C

of

ABC

, there is

no match (zero numeric digits fails to match the criterion “one or more numeric digits,” specified by the

+

quantifier). Because the final component of the pattern fails to match, the whole pattern fails to match.

Why does the part number

ABC8899

match? When the regular expression engine is at the position imme-

diately before the

A

of

ABC8899

, it attempts to match the next character in the part number with an upper-

case

A

. Because the first character of the part number

ABC8899

is an uppercase

A

, there is a match. Next,

335

Appendix A: Simple Regular Expressions

bapp01.qxd:bapp01 10:47 335

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