Programming PHP

Table 4-7. POSIX character classes (continued)
Class Description Expansion
[:ascii:] 7-bit ASCII [\x01-\x7F]
[:blank:] Horizontal whitespace (space, tab) [ \t]
[:cntrl:] Control characters [\x01-\x1F]
[:digit:] Digits [0-9]
[:graph:] Characters that use ink to print (non-space,
non-control)
[^\x01-\x20]
[:lower:] Lowercase letter [a-z]
[:print:] Printable character (graph class plus space and
tab)
[\t\x20-\xFF]
[:punct:] Any punctuation character, such as the period (.)
and the semicolon (;)
[-!"#$%&'( )*+,./:;?@[\\]^_`{|}~]
[:space:] Whitespace (newline, carriage return, tab, space,
vertical tab)
[\n\r\t \x0B]
[:upper:] Uppercase letter [A-Z]
[:xdigit:] Hexadecimal digit [0-9a-fA-F]
Each [:something:] class can be used in place of a character in a character class. For
instance, to find any character that’s a digit, an uppercase letter, or an at sign (@), use
the following regular expression:
[@[:digit:][:upper:]]
However, you can’t use a character class as the endpoint of a range:
ereg('[A-[:lower:]]', 'string'); // invalid regular expression
Some locales consider certain character sequences as if they were a single character—
these are called collating sequences. To match one of these multicharacter sequences
in a character class, enclose it with [. and .]. For example, if your locale has the collating
sequence ch, you can match s, t, or ch with this character class:
[st[.ch.]]
The final POSIX extension to character classes is the equivalence class, specified by
enclosing the character in [= and =]. Equivalence classes match characters that have
the same collating order, as defined in the current locale. For example, a locale may
define a, á, and ä as having the same sorting precedence. To match any one of them,
the equivalence class is [=a=].
Anchors
An anchor limits a match to a particular location in the string (anchors do not match
actual characters in the target string). Table 4-8 lists the anchors supported by
POSIX regular expressions.
100 | Chapter 4: Strings
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