Specifications

TABLE 4.3 Character Classes for Use in POSIX-Style Regular Expressions

Class Matches

[[:alnum:]] Alphanumeric characters

[[:alpha:]] Alphabetic characters

[[:lower:]] Lowercase letters

[[:upper:]] Uppercase letters

[[:digit:]] Decimal digits

[[:xdigit:]] Hexadecimal digits

[[:punct:]] Punctuation

[[:blank:]] Tabs and spaces

[[:space:]] Whitespace characters

[[:cntrl:]] Control characters

[[:print:]] All printable characters

[[:graph:]] All printable characters except for space

Repetition

Often you want to specify that there might be multiple occurrences of a particular string or

class of character. You can represent this using two special characters in your regular expres-

sion. The * symbol means that the pattern can be repeated zero or more times, and the + sym-

bol means that the pattern can be repeated one or more times. The symbol should appear

directly after the part of the expression that it applied to. For example

[[:alnum:]]+

means “at least one alphanumeric character.”

Subexpressions

It’s often useful to be able to split an expression into subexpressions so you can, for example,

represent “at least one of these strings followed by exactly one of those.” You can do this using

parentheses, exactly the same way as you would in an arithmetic expression. For example,

(very )*large

matches “large”, “very large”, “very very large”, and so on.

String Manipulation and Regular Expressions

HAPTER 4

TRING

ANIPULATION

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