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Meta-Character
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Description |
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^
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This meta-character, the caret, matches the beginning of a
string or, if the /m option isused, match the beginning of a
line. It is one oftwo pattern anchors, the other anchor is the $.
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.
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This meta-character will match any single character except
for the newline character unless the /s option is specified.
If the /s option is specified, then the newline will also be
matched. |
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$
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This meta-character will match the end of a string or,if the
/m option is used, match the end of a line.It is one of two pattern
anchors; the other anchoris the ^. |
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|
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This meta-character, called alternation, lets you specify
two values that can cause the match to succe|ed. For instance, m/a|b/
means that the $_variable must contain the "a" or "b"
character forthe match to succeed. |
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*
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This meta-character indicates that the "thing" immediately
to the left should be matched zero or more times in order to be evaluated
as true (thus .*matches any number of characters). |
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+
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This meta-character indicates that the "thing" immediately
to the left should be matched one or more times in order to be evaluated
as true. |
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?
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This meta-character indicates that the "thing" immediately
to the left should be matched zero or one times to be evaluated as true.
When used inconjunction with the +, ?, or {n, m}
meta-characters and brackets, it means that the regular expression should
be non-greedy and match the smallest possible string. |
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Meta-Brackets
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Description |
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()
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The parentheses let you affect the order of pattern evaluation
and act as a form of pattern memory. See the "Special Variables"
chapter for moredetails. |
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(?...)
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If a question mark immediately follows the left parentheses,
it indicates that an extended mode component is being specified; this
is new to Perl 5. |
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(?#comment)
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Extension: comment is any text. |
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(?:regx)
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Extension: regx is any regular expression but ()
are not saved as a backreference. |
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(?=regx)
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Extension: Allows matching of zero-width positive lookahead
characters (that is, the regular expression is matched but not returned
as being matched). |
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(?!regx)
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Extension: Allows matching of zero-width negative lookahead
characters (that is, negated form of (=regx)). |
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(?options)
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Extension: Applies the specified options to the pattern
bypassing the need for the option to specified in the normal way. Valid
options are: i (case insenstive), m (treat as multiple
lines), s (treat as single line), and x (allow whitespace
and comments). |
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{n, m}
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Braces let you specify how many times the "thing"
immediately to the left should be matched. {n} means that it
should be matched exactly n times. {n,} means it must
be matched at least n times. {n, m} means that it must
be matched at least n times but not more than m times.
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[]
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Square brackets let you create a character class. For instance,
m/[abc]/ evaluates to True if any of "a", "b",
or "c" is contained in $_. The square brackets are
a more readable alternative to the alternation meta-character. |
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Meta-Sequences
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Description |
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\
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This meta-character "escapes" the character which
follows. This means that any special meaning normally attached to that
character is ignored. For instance, if you need to include a dollar sign
in a pattern, you must use \$ to avoid Perl's variable interpolation.
Use \\ to specify the backslash character in your pattern. |
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\nnn
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Any octal byte where nnn represents the octal number;
this allows any character to be specified by its octal number. |
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\a
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The alarm character; this is a special character which, when
printed, produces a warning bell sound. |
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\A
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This meta-sequence represents the beginning of the string.
Its meaning is not affected by the /m option. |
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\b
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This meta-sequence represents the backspace character inside
a character class; otherwise, it represents a word boundary. A word boundary
is the spot between word (\w) and non-word (\W) characters.
Perl thinks that the \W meta-sequence matches the imaginary characters
of the end of the string. |
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\B
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Match a non-word boundary. |
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\cn
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Any control character where n is the character (for
example, \cY for Ctrl+Y). |
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\d
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Match a single digit character. |
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\D
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Match a single non-digit character. |
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\e
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The escape character. |
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\E
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Terminate the \L or \U sequence. |
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\f
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The form feed character. |
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\G
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Match only where the previous m//g left off. |
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\l
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Change the next character to lowercase. |
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\L
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Change the following characters to lowercase until a \E
sequence is encountered. |
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\n
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The newline character. |
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\Q
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Quote regular expression meta-characters literally until the
\E sequence is encountered. |
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\r
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The carriage return character. |
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\s
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Match a single whitespace character. |
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\S
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Match a single non-whitespace character. |
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\t
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The tab character. |
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\u
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Change the next character to uppercase. |
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\U
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Change the following characters to uppercase until a \E
sequence is encountered. |
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\v
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The vertical tab character. |
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\w
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Match a single word character. Word characters are the alphanumeric
and underscore characters. |
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\W
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Match a single non-word character. |
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\xnn
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Any hexadecimal byte. |
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\Z
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This meta-sequence represents the end of the string. Its meaning
is not affected by the /m option. |
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\$
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The dollar character. |
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\@
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The ampersand character. |
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\%
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The percent character. |
