Programming Perl, 4th Edition

Metasymbol Tables

In the following tables, the Atomic column says “yes” if the given metasymbol is quantifiable (if it can match something with width, more or less). Also, we’ve used “...” to represent “something else”. (Please see the later discussion to find out what “...” means, if it is not clear from the one-line gloss in the table.)

Table 5-6 shows the basic traditional metasymbols. The first four of these are the structural metasymbols we mentioned earlier, while the last three are simple metacharacters. The . metacharacter is an example of an atom because it matches something with width (the width of a character, in this case); ^ and $ are examples of assertions, because they match something of zero width, and because they are only evaluated to see whether they’re true.

Table 5-6. General regex metacharacters

Symbol	Atomic	Meaning
\...	Varies	(De)meta next (non)alphanumeric character alphanumeric character (maybe)
...|...	No	Alternation (match one or the other)
(...)	Yes	Grouping (treat as a unit)
[...]	Yes	Character class (match one character from a set)
^	No	True at beginning of string (or after any newline, maybe)
.	Yes	Match one character (except newline, normally)
$	No	True at end of string (or before any newline, maybe)

The quantifiers, which are further described in their own section, indicate how many times the preceding atom (that is, single character or grouping) should match. These are listed in Table 5-7.

Table 5-7. Regex quantifiers

Maximal	Minimal	Possessive	Allowed Range
{MIN,MAX}	{MIN,MAX ...