The rules determining what it is are quite simple: if the character
following the backslash is an ASCII punctuation (non-word) character (that is,
-anything that is not a letter, digit or underscore), then the backslash just
-takes away the special meaning (if any) of the character following it.
+anything that is not a letter, digit, or underscore), then the backslash just
+takes away any special meaning of the character following it.
If the character following the backslash is an ASCII letter or an ASCII digit,
then the sequence may be special; if so, it's listed below. A few letters have
not been used yet, so escaping them with a backslash doesn't change them to be
special. A future version of Perl may assign a special meaning to them, so if
-you have warnings turned on, Perl will issue a warning if you use such a
+you have warnings turned on, Perl issues a warning if you use such a
sequence. [1].
It is however guaranteed that backslash or escape sequences never have a
=item [1]
-There is one exception. If you use an alphanumerical character as the
+There is one exception. If you use an alphanumeric character as the
delimiter of your pattern (which you probably shouldn't do for readability
-reasons), you will have to escape the delimiter if you want to match
+reasons), you have to escape the delimiter if you want to match
it. Perl won't warn then. See also L<perlop/Gory details of parsing
quoted constructs>.
=item [2]
-C<\n> matches a logical newline. Perl will convert between C<\n> and your
+C<\n> matches a logical newline. Perl converts between C<\n> and your
OS's native newline character when reading from or writing to text files.
=back
To specify by name, the name of the character or character sequence goes
between the curly braces. In this case, you have to C<use charnames> to
-load the Unicode names of the characters, otherwise Perl will complain.
+load the Unicode names of the characters; otherwise Perl will complain.
-To specify a character by Unicode code point, use the form
-C<\N{U+I<wide hex character>}>, where I<wide hex character> is a number in
-hexadecimal that gives the ordinal number that Unicode has assigned to the
-desired character. It is customary (but not required) to use leading zeros to
-pad the number to 4 digits. Thus C<\N{U+0041}> means
-C<LATIN CAPITAL LETTER A>, and you will rarely see it written without the two
-leading zeros. C<\N{U+0041}> means "A" even on EBCDIC machines (where the
-ordinal value of "A" is not 0x41).
+To specify a character by Unicode code point, use the form C<\N{U+I<code
+point>}>, where I<code point> is a number in hexadecimal that gives the
+ordinal number that Unicode has assigned to the desired character. It is
+customary but not required to use leading zeros to pad the number to 4
+digits. Thus C<\N{U+0041}> means C<LATIN CAPITAL LETTER A>, and you will
+rarely see it written without the two leading zeros. C<\N{U+0041}> means
+"A" even on EBCDIC machines (where the ordinal value of "A" is not 0x41).
It is even possible to give your own names to characters and character
sequences. For details, see L<charnames>.
(There is an expanded internal form that you may see in debug output:
-C<\N{U+I<wide hex character>.I<wide hex character>...}>.
-The C<...> means any number of these I<wide hex character>s separated by dots.
+C<\N{U+I<code point>.I<code point>...}>.
+The C<...> means any number of these I<code point>s separated by dots.
This represents the sequence formed by the characters. This is an internal
form only, subject to change, and you should not try to use it yourself.)
Mnemonic: I<N>amed character.
-Note that a character or character sequence that is expressed as a named
-or numbered character is considered as a character without special
+Note that a character or character sequence expressed as a named
+or numbered character is considered a character without special
meaning by the regex engine, and will match "as is".
=head4 Example
ending of the snippet before it. See L</Absolute referencing> for more
discussion and examples of the snippet problem.
-Note that a character that is expressed as an octal escape is considered
-as a character without special meaning by the regex engine, and will match
+Note that a character expressed as an octal escape is considered
+a character without special meaning by the regex engine, and will match
"as is".
To summarize, the C<\o{}> form is always safe to use, and the other form is
=item 3
-If the number following the backslash is N (in decimal), and Perl already has
-seen N capture groups, Perl will consider this to be a backreference.
-Otherwise, it will consider it to be an octal escape. Note that if N has more
-than three digits, Perl only takes the first three for the octal escape;
-the rest are matched as is.
+If the number following the backslash is N (in decimal), and Perl already
+has seen N capture groups, Perl considers this a backreference. Otherwise,
+it considers it an octal escape. If N has more than three digits, Perl
+takes only the first three for the octal escape; the rest are matched as is.
my $pat = "(" x 999;
$pat .= "a";
by curly braces. The hexadecimal number is the code point of the character you
want to express.
-Note that a character that is expressed as one of these escapes is considered
-as a character without special meaning by the regex engine, and will match
+Note that a character expressed as one of these escapes is considered a
+character without special meaning by the regex engine, and will match
"as is".
Mnemonic: heI<x>adecimal.
A number of backslash sequences have to do with changing the character,
or characters following them. C<\l> will lowercase the character following
it, while C<\u> will uppercase (or, more accurately, titlecase) the
-character following it. (They perform similar functionality as the
-functions C<lcfirst> and C<ucfirst>).
+character following it. They provide functionality similar to the
+functions C<lcfirst> and C<ucfirst>.
To uppercase or lowercase several characters, one might want to use
C<\L> or C<\U>, which will lowercase/uppercase all characters following
-them, until either the end of the pattern, or the next occurrence of
-C<\E>, whatever comes first. They perform similar functionality as the
-functions C<lc> and C<uc> do.
+them, until either the end of the pattern or the next occurrence of
+C<\E>, whatever comes first. They provide functionality similar to what
+the functions C<lc> and C<uc> provide.
C<\Q> is used to escape all characters following, up to the next C<\E>
or the end of the pattern. C<\Q> adds a backslash to any character that
-isn't a letter, digit or underscore. This will ensure that any character
-between C<\Q> and C<\E> is matched literally, and will not be interpreted
-by the regexp engine.
+isn't a letter, digit, or underscore. This ensures that any character
+between C<\Q> and C<\E> shall be matched literally, not interpreted
+as a metacharacter by the regex engine.
Mnemonic: I<L>owercase, I<U>ppercase, I<Q>uotemeta, I<E>nd.
probably not what you intended.
In the C<\I<N>> form, I<N> must not begin with a "0", and there must be at
-least I<N> capturing groups, or else I<N> will be considered an octal escape
-(but something like C<\18> is the same as C<\0018>, that is the octal escape
+least I<N> capturing groups, or else I<N> is considered an octal escape
+(but something like C<\18> is the same as C<\0018>; that is, the octal escape
C<"\001"> followed by a literal digit C<"8">).
Mnemonic: I<g>roup.
=item \z, \Z
C<\z> and C<\Z> match at the end of the string. If the C</m> modifier isn't
-used, then C</\Z/> is equivalent to C</$/>, that is, it matches at the
-end of the string, or before the newline at the end of the string. If the
+used, then C</\Z/> is equivalent to C</$/>; that is, it matches at the
+end of the string, or one before the newline at the end of the string. If the
C</m> modifier is used, then C</$/> matches at internal newlines, but the
meaning of C</\Z/> isn't changed by the C</m> modifier. C<\Z> matches at
the end of the string (or just before a trailing newline) regardless whether
the C</m> modifier is used.
-C<\z> is just like C<\Z>, except that it will not match before a trailing
-newline. C<\z> will only match at the end of the string - regardless of the
-modifiers used, and not before a newline.
+C<\z> is just like C<\Z>, except that it does not match before a trailing
+newline. C<\z> matches at the end of the string only, regardless of the
+modifiers used, and not just before a newline. It is how to anchor the
+match to the true end of the string under all conditions.
=item \G
-C<\G> is usually only used in combination with the C</g> modifier. If the
-C</g> modifier is used (and the match is done in scalar context), Perl will
-remember where in the source string the last match ended, and the next time,
+C<\G> is usually used only in combination with the C</g> modifier. If the
+C</g> modifier is used and the match is done in scalar context, Perl
+remembers where in the source string the last match ended, and the next time,
it will start the match from where it ended the previous time.
-C<\G> matches the point where the previous match ended, or the beginning
-of the string if there was no previous match.
+C<\G> matches the point where the previous match on that string ended,
+or the beginning of that string if there was no previous match.
=for later add link to perlremodifiers
and C<\B> assume there's a non-word character before the beginning and after
the end of the source string; so C<\b> will match at the beginning (or end)
of the source string if the source string begins (or ends) with a word
-character. Otherwise, C<\B> will match.
+character. Otherwise, C<\B> will match.
+
+Do not use something like C<\b=head\d\b> and expect it to match the
+beginning of a line. It can't, because for there to be a boundary before
+the non-word "=", there must be a word character immediately previous.
+All boundary determinations look for word characters alone, not for
+non-words characters nor for string ends. It may help to understand how
+<\b> and <\B> work by equating them as follows:
+
+ \b really means (?:(?<=\w)(?!\w)|(?<!\w)(?=\w))
+ \B really means (?:(?<=\w)(?=\w)|(?<!\w)(?!\w))
Mnemonic: I<b>oundary.
=head2 Misc
Here we document the backslash sequences that don't fall in one of the
-categories above. They are:
+categories above. These are:
=over 4
C<\C> always matches a single octet, even if the source string is encoded
in UTF-8 format, and the character to be matched is a multi-octet character.
-C<\C> was introduced in perl 5.6.
+C<\C> was introduced in perl 5.6. This is very dangerous, because it violates
+the logical character abstraction and can cause UTF-8 sequences to become malformed.
Mnemonic: oI<C>tet.
=item \K
-This is new in perl 5.10.0. Anything that is matched left of C<\K> is
-not included in C<$&> - and will not be replaced if the pattern is
-used in a substitution. This will allow you to write C<s/PAT1 \K PAT2/REPL/x>
+This appeared in perl 5.10.0. Anything matched left of C<\K> is
+not included in C<$&>, and will not be replaced if the pattern is
+used in a substitution. This lets you write C<s/PAT1 \K PAT2/REPL/x>
instead of C<s/(PAT1) PAT2/${1}REPL/x> or C<s/(?<=PAT1) PAT2/REPL/x>.
Mnemonic: I<K>eep.
=item \N
-This is a new experimental feature in perl 5.12.0. It matches any character
-that is not a newline. It is a short-hand for writing C<[^\n]>, and is
+This is an experimental feature new to perl 5.12.0. It matches any character
+that is B<not> a newline. It is a short-hand for writing C<[^\n]>, and is
identical to the C<.> metasymbol, except under the C</s> flag, which changes
the meaning of C<.>, but not C<\N>.
=item \R
X<\R>
-C<\R> matches a I<generic newline>, that is, anything that is considered
-a newline by Unicode. This includes all characters matched by C<\v>
-(vertical whitespace), and the multi character sequence C<"\x0D\x0A">
-(carriage return followed by a line feed, aka the network newline, or
-the newline used in Windows text files). C<\R> is equivalent to
-C<< (?>\x0D\x0A)|\v) >>. Since C<\R> can match a sequence of more than one
-character, it cannot be put inside a bracketed character class; C</[\R]/> is an
-error; use C<\v> instead. C<\R> was introduced in perl 5.10.0.
+C<\R> matches a I<generic newline>; that is, anything considered a
+linebreak sequence by Unicode. This includes all characters matched by
+C<\v> (vertical whitespace), and the multi character sequence C<"\x0D\x0A">
+(carriage return followed by a line feed, sometimes called the network
+newline; it's the end of line sequence used in Microsoft text files opened
+in binary mode). C<\R> is equivalent to C<< (?>\x0D\x0A)|\v) >>. Since
+C<\R> can match a sequence of more than one character, it cannot be put
+inside a bracketed character class; C</[\R]/> is an error; use C<\v>
+instead. C<\R> was introduced in perl 5.10.0.
Mnemonic: none really. C<\R> was picked because PCRE already uses C<\R>,
and more importantly because Unicode recommends such a regular expression
-metacharacter, and suggests C<\R> as the notation.
+metacharacter, and suggests C<\R> as its notation.
=item \X
X<\X>
=head4 Examples
- "\x{256}" =~ /^\C\C$/; # Match as chr (256) takes 2 octets in UTF-8.
+ "\x{256}" =~ /^\C\C$/; # Match as chr (0x256) takes 2 octets in UTF-8.
$str =~ s/foo\Kbar/baz/g; # Change any 'bar' following a 'foo' to 'baz'
$str =~ s/(.)\K\g1//g; # Delete duplicated characters.
"\r" =~ /^\R$/; # Match, \r is a generic newline.
"\r\n" =~ /^\R$/; # Match, \r\n is a generic newline.
- "P\x{0307}" =~ /^\X$/ # \X matches a P with a dot above.
+ "P\x{307}" =~ /^\X$/ # \X matches a P with a dot above.
=cut
=head3 Digits
-C<\d> matches a single character that is considered to be a decimal I<digit>.
+C<\d> matches a single character considered to be a decimal I<digit>.
What is considered a decimal digit depends on several factors, detailed
below in L</Locale, EBCDIC, Unicode and UTF-8>. If those factors
indicate a Unicode interpretation, C<\d> not only matches the digits
-'0' - '9', but also Arabic, Devanagari and digits from other languages.
-Otherwise, if there is a locale in effect, it will match whatever
-characters the locale considers decimal digits. Without a locale, C<\d>
-matches just the digits '0' to '9'.
+'0' - '9', but also Arabic, Devanagari, and digits from other languages.
+Otherwise, if a locale is in effect, it matches whatever characters that
+locale considers decimal digits. Only when neither a Unicode interpretation
+nor locale prevails does C<\d> match only the digits '0' to '9' alone.
Unicode digits may cause some confusion, and some security issues. In UTF-8
strings, unless the C<"a"> regular expression modifier is specified,
C<\p{Numeric_Type=Digit}>, which matches a completely different set of
characters. These characters are things such as subscripts.
-The design intent is for C<\d> to match all the digits (and no other characters)
+The design intent is for C<\d> to match all digits (and no other characters)
that can be used with "normal" big-endian positional decimal syntax, whereby a
sequence of such digits {N0, N1, N2, ...Nn} has the numeric value (...(N0 * 10
+ N1) * 10 + N2) * 10 ... + Nn). In Unicode 5.2, the Tamil digits (U+0BE6 -
appear no more than one in a row, separated by characters that mean "times 10",
"times 100", etc. (See L<http://www.unicode.org/notes/tn21>.)
-Some of the non-European digits that C<\d> matches look like European ones, but
+Some non-European digits that C<\d> matches look like European ones, but
have different values. For example, BENGALI DIGIT FOUR (U+09EA) looks
very much like an ASCII DIGIT EIGHT (U+0038).
It may be useful for security purposes for an application to require that all
digits in a row be from the same script. See L<Unicode::UCD/charscript()>.
-Any character that isn't matched by C<\d> will be matched by C<\D>.
+Any character not matched by C<\d> is matched by C<\D>.
=head3 Word characters
characters. What is considered a
word character depends on several factors, detailed below in L</Locale,
EBCDIC, Unicode and UTF-8>. If those factors indicate a Unicode
-interpretation, C<\w> matches the characters that are considered word
+interpretation, C<\w> matches the characters considered word
characters in the Unicode database. That is, it not only matches ASCII letters,
but also Thai letters, Greek letters, etc. This includes connector
punctuation (like the underscore) which connect two words together, or
-marks, such as a C<COMBINING TILDE>, which are generally used to add
-diacritical marks to letters. If a Unicode interpretation
-is not indicated, C<\w> matches those characters that are considered
+diacritics, such as a C<COMBINING TILDE> and the modifier letters, which
+are generally used to add auxiliary markings to letters. If a Unicode
+interpretation is not indicated, C<\w> matches those characters considered
word characters by the current locale or EBCDIC code page. Without a
-locale or EBCDIC code page, C<\w> matches the ASCII letters, digits and
-the underscore.
+locale or EBCDIC code page, C<\w> matches the underscore and ASCII letters
+and digits.
There are a number of security issues with the full Unicode list of word
characters. See L<http://unicode.org/reports/tr36>.
more customized Unicode properties, "ID_Start", ID_Continue", "XID_Start", and
"XID_Continue". See L<http://unicode.org/reports/tr31>.
-Any character that isn't matched by C<\w> will be matched by C<\W>.
+Any character not matched by C<\w> is matched by C<\W>.
=head3 Whitespace
-C<\s> matches any single character that is considered whitespace. The exact
+C<\s> matches any single character considered whitespace. The exact
set of characters matched by C<\s> depends on several factors, detailed
below in L</Locale, EBCDIC, Unicode and UTF-8>. If those factors
indicate a Unicode interpretation, C<\s> matches what is considered
whitespace in the Unicode database; the complete list is in the table
-below. Otherwise, if there is a locale or EBCDIC code page in effect,
+below. Otherwise, if a locale or EBCDIC code page is in effect,
C<\s> matches whatever is considered whitespace by the current locale or
EBCDIC code page. Without a locale or EBCDIC code page, C<\s> matches
the horizontal tab (C<\t>), the newline (C<\n>), the form feed (C<\f>),
the carriage return (C<\r>), and the space. (Note that it doesn't match
the vertical tab, C<\cK>.) Perhaps the most notable possible surprise
-is that C<\s> matches a non-breaking space only if a Unicode
+is that C<\s> matches a non-breaking space B<only> if a Unicode
interpretation is indicated, or the locale or EBCDIC code page that is
-in effect has that character.
+in effect happens to have that character.
-Any character that isn't matched by C<\s> will be matched by C<\S>.
+Any character not matched by C<\s> is matched by C<\S>.
-C<\h> will match any character that is considered horizontal whitespace;
-this includes the space and the tab characters and a number other characters,
-all of which are listed in the table below. C<\H> will match any character
-that is not considered horizontal whitespace.
+C<\h> matches any character considered horizontal whitespace;
+this includes the space and tab characters and several others
+listed in the table below. C<\H> matches any character
+not considered horizontal whitespace.
-C<\v> will match any character that is considered vertical whitespace;
-this includes the carriage return and line feed characters (newline) plus several
-other characters, all listed in the table below.
-C<\V> will match any character that is not considered vertical whitespace.
+C<\v> matches any character considered vertical whitespace;
+this includes the carriage return and line feed characters (newline)
+plus several other characters, all listed in the table below.
+C<\V> matches any character not considered vertical whitespace.
C<\R> matches anything that can be considered a newline under Unicode
rules. It's not a character class, as it can match a multi-character
Details are discussed in L<perlrebackslash>.
Note that unlike C<\s>, C<\d> and C<\w>, C<\h> and C<\v> always match
-the same characters, without regard to other factors, such as if the
-source string is in UTF-8 format or not.
+the same characters, without regard to other factors, such as whether the
+source string is in UTF-8 format.
One might think that C<\s> is equivalent to C<[\h\v]>. This is not true. The
vertical tab (C<"\x0b">) is not matched by C<\s>, it is however considered
and any locale or EBCDIC code page that is in effect doesn't include them, the
next line (ASCII-platform C<"\x85">) and the no-break space (ASCII-platform
C<"\xA0">) characters are not matched by C<\s>, but are by C<\v> and C<\h>
-respectively. If the C<"a"> modifier is not in effect, and the source
-string is in UTF-8 format, both the next line and
-the no-break space are matched by C<\s>.
+respectively. If the C<"a"> modifier is not in effect and the source
+string is in UTF-8 format, both the next line and the no-break space
+are matched by C<\s>.
The following table is a complete listing of characters matched by
C<\s>, C<\h> and C<\v> as of Unicode 5.2.
=item [1]
NEXT LINE and NO-BREAK SPACE only match C<\s> if the source string is in
-UTF-8 format and the C<"a"> modifier is not in effect; or the locale or
-EBCDIC code page that is in effect includes them.
+UTF-8 format and the C<"a"> modifier is not in effect, or if the locale
+or EBCDIC code page in effect includes them.
=back
=head3 \N
-C<\N> is new in 5.12, and is experimental. It, like the dot, will match any
+C<\N> is new in 5.12, and is experimental. It, like the dot, matches any
character that is not a newline. The difference is that C<\N> is not influenced
by the I<single line> regular expression modifier (see L</The dot> above). Note
that the form C<\N{...}> may mean something completely different. When the
is not a legal quantifier, it is presumed to be a named character. See
L<charnames> for those. For example, none of C<\N{COLON}>, C<\N{4F}>, and
C<\N{F4}> contain legal quantifiers, so Perl will try to find characters whose
-names are, respectively, C<COLON>, C<4F>, and C<F4>.
+names are respectively C<COLON>, C<4F>, and C<F4>.
=head3 Unicode Properties
with the property name following the C<\p>, otherwise, braces are required.
When using braces, there is a single form, which is just the property name
enclosed in the braces, and a compound form which looks like C<\p{name=value}>,
-which means to match if the property "name" for the character has the particular
+which means to match if the property "name" for the character has that particular
"value".
For instance, a match for a number can be written as C</\pN/> or as
C</\p{Number}/>, or as C</\p{Number=True}/>.
Note that almost all properties are immune to case-insensitive matching.
That is, adding a C</i> regular expression modifier does not change what
-they match. There are two sets that are affected. The first set is
+they match. There are two sets affected. The first set is
C<Uppercase_Letter>,
C<Lowercase_Letter>,
and C<Titlecase_Letter>,
all of which match C<Cased_Letter> under C</i> matching.
-And the second set is
+The second set is
C<Uppercase>,
C<Lowercase>,
and C<Titlecase>,
all of which match C<Cased> under C</i> matching.
(The difference between these sets is that some things, such as Roman
-Numerals come in both upper and lower case so they are C<Cased>, but
-aren't considered to be letters, so they aren't C<Cased_Letter>s.)
-This set also includes its subsets C<PosixUpper> and C<PosixLower> both
+Numerals, come in both upper and lower case so they are C<Cased>, but
+aren't considered to be letters, so they aren't C<Cased_Letter>s. They're
+actually C<Letter_Number>s.)
+This set also includes its subsets C<PosixUpper> and C<PosixLower>, both
of which under C</i> matching match C<PosixAlpha>.
For more details on Unicode properties, see L<perlunicode/Unicode
is the bracketed character class. In its simplest form, it lists the characters
that may be matched, surrounded by square brackets, like this: C<[aeiou]>.
This matches one of C<a>, C<e>, C<i>, C<o> or C<u>. Like the other
-character classes, exactly one character will be matched. To match
+character classes, exactly one character is matched. To match
a longer string consisting of characters mentioned in the character
class, follow the character class with a L<quantifier|perlre/Quantifiers>. For
-instance, C<[aeiou]+> matches a string of one or more lowercase English vowels.
+instance, C<[aeiou]+> matches one or more lowercase English vowels.
Repeating a character in a character class has no
effect; it's considered to be in the set only once.
L</POSIX Character Classes> below), or it signals the end of the bracketed
character class. If you want to include a C<]> in the set of characters, you
must generally escape it.
+
However, if the C<]> is the I<first> (or the second if the first
character is a caret) character of a bracketed character class, it
does not denote the end of the class (as you cannot have an empty class)
=head3 Character Ranges
It is not uncommon to want to match a range of characters. Luckily, instead
-of listing all the characters in the range, one may use the hyphen (C<->).
+of listing all characters in the range, one may use the hyphen (C<->).
If inside a bracketed character class you have two characters separated
-by a hyphen, it's treated as if all the characters between the two are in
+by a hyphen, it's treated as if all characters between the two were in
the class. For instance, C<[0-9]> matches any ASCII digit, and C<[a-m]>
-matches any lowercase letter from the first half of the ASCII alphabet.
+matches any lowercase letter from the first half of the old ASCII alphabet.
Note that the two characters on either side of the hyphen are not
necessarily both letters or both digits. Any character is possible,
although not advisable. C<['-?]> contains a range of characters, but
-most people will not know which characters that will be. Furthermore,
+most people will not know which characters that means. Furthermore,
such ranges may lead to portability problems if the code has to run on
a platform that uses a different character set, such as EBCDIC.
If a hyphen in a character class cannot syntactically be part of a range, for
instance because it is the first or the last character of the character class,
-or if it immediately follows a range, the hyphen isn't special, and will be
-considered a character that is to be matched literally. You have to escape the
-hyphen with a backslash if you want to have a hyphen in your set of characters
-to be matched, and its position in the class is such that it could be
-considered part of a range.
+or if it immediately follows a range, the hyphen isn't special, and so is
+considered a character to be matched literally. If you want a hyphen in
+your set of characters to be matched and its position in the class is such
+that it could be considered part of a range, you must escape that hyphen
+with a backslash.
Examples:
It is also possible to instead list the characters you do not want to
match. You can do so by using a caret (C<^>) as the first character in the
-character class. For instance, C<[^a-z]> matches a character that is not a
-lowercase ASCII letter.
+character class. For instance, C<[^a-z]> matches any character that is not a
+lowercase ASCII letter, which therefore includes almost a hundred thousand
+Unicode letters.
This syntax make the caret a special character inside a bracketed character
class, but only if it is the first character of the class. So if you want
-to have the caret as one of the characters you want to match, you either
-have to escape the caret, or not list it first.
+the caret as one of the characters to match, either escape the caret or
+else not list it first.
Examples:
You can put any backslash sequence character class (with the exception of
C<\N> and C<\R>) inside a bracketed character class, and it will act just
-as if you put all the characters matched by the backslash sequence inside the
-character class. For instance, C<[a-f\d]> will match any decimal digit, or any
+as if you had put all characters matched by the backslash sequence inside the
+character class. For instance, C<[a-f\d]> matches any decimal digit, or any
of the lowercase letters between 'a' and 'f' inclusive.
C<\N> within a bracketed character class must be of the forms C<\N{I<name>}>
The latter pattern would be a character class consisting of a colon,
and the letters C<a>, C<l>, C<p> and C<h>.
-POSIX character classes can be part of a larger bracketed character class. For
-example,
+POSIX character classes can be part of a larger bracketed character class.
+For example,
[01[:alpha:]%]
Perl recognizes the following POSIX character classes:
alpha Any alphabetical character ("[A-Za-z]").
- alnum Any alphanumerical character. ("[A-Za-z0-9]")
+ alnum Any alphanumeric character. ("[A-Za-z0-9]")
ascii Any character in the ASCII character set.
blank A GNU extension, equal to a space or a horizontal tab ("\t").
cntrl Any control character. See Note [2] below.
between POSIX character classes and these counterparts.
One counterpart, in the column labelled "ASCII-range Unicode" in
-the table, will only match characters in the ASCII character set.
+the table, matches only characters in the ASCII character set.
The other counterpart, in the column labelled "Full-range Unicode", matches any
appropriate characters in the full Unicode character set. For example,
-C<\p{Alpha}> will match not just the ASCII alphabetic characters, but any
-character in the entire Unicode character set that is considered to be
-alphabetic. The column labelled "backslash sequence" is a (short) synonym for
+C<\p{Alpha}> matches not just the ASCII alphabetic characters, but any
+character in the entire Unicode character set considered alphabetic.
+The column labelled "backslash sequence" is a (short) synonym for
the Full-range Unicode form.
(Each of the counterparts has various synonyms as well.
-L<perluniprops/Properties accessible through \p{} and \P{}> lists all the
-synonyms, plus all the characters matched by each of the ASCII-range
-properties. For example C<\p{AHex}> is a synonym for C<\p{ASCII_Hex_Digit}>,
+L<perluniprops/Properties accessible through \p{} and \P{}> lists all
+synonyms, plus all characters matched by each ASCII-range property.
+For example, C<\p{AHex}> is a synonym for C<\p{ASCII_Hex_Digit}>,
and any C<\p> property name can be prefixed with "Is" such as C<\p{IsAlpha}>.)
-Both the C<\p> forms are unaffected by any locale that is in effect, or whether
+Both the C<\p> forms are unaffected by any locale in effect, or whether
the string is in UTF-8 format or not, or whether the platform is EBCDIC or not.
In contrast, the POSIX character classes are affected, unless the
regular expression is compiled with the C<"a"> modifier. If the C<"a">
=item [2]
Control characters don't produce output as such, but instead usually control
-the terminal somehow: for example newline and backspace are control characters.
+the terminal somehow: for example, newline and backspace are control characters.
In the ASCII range, characters whose ordinals are between 0 and 31 inclusive,
plus 127 (C<DEL>) are control characters.
=item [3]
Any character that is I<graphical>, that is, visible. This class consists
-of all the alphanumerical characters and all punctuation characters.
+of all alphanumeric characters and all punctuation characters.
=item [4]
-All printable characters, which is the set of all the graphical characters
-plus whitespace characters that are not also controls.
+All printable characters, which is the set of all graphical characters
+plus those whitespace characters which are not also controls.
=item [5]
-C<\p{PosixPunct}> and C<[[:punct:]]> in the ASCII range match all the
+C<\p{PosixPunct}> and C<[[:punct:]]> in the ASCII range match all
non-controls, non-alphanumeric, non-space characters:
C<[-!"#$%&'()*+,./:;<=E<gt>?@[\\\]^_`{|}~]> (although if a locale is in effect,
it could alter the behavior of C<[[:punct:]]>).
C<\p{PosixPunct}> matches in the ASCII range, plus what C<\p{Punct}>
matches. This is different than strictly matching according to
C<\p{Punct}>. Another way to say it is that
-for a UTF-8 string, C<[[:punct:]]> matches all the characters that Unicode
-considers to be punctuation, plus all the ASCII-range characters that Unicode
-considers to be symbols.
+for a UTF-8 string, C<[[:punct:]]> matches all characters that Unicode
+considers punctuation, plus all ASCII-range characters that Unicode
+considers symbols.
=item [6]
=back
There are various other synonyms that can be used for these besides
-C<\p{HorizSpace}> and \C<\p{XPosixBlank}>. For example
+C<\p{HorizSpace}> and \C<\p{XPosixBlank}>. For example,
C<\p{PosixAlpha}> can be written as C<\p{Alpha}>. All are listed
in L<perluniprops/Properties accessible through \p{} and \P{}>.
=head4 [= =] and [. .]
-Perl will recognize the POSIX character classes C<[=class=]>, and
-C<[.class.]>, but does not (yet?) support them. Use of
-such a construct will lead to an error.
-
+Perl recognizes the POSIX character classes C<[=class=]> and
+C<[.class.]>, but does not (yet?) support them. Any attempt to use
+either construct raises an exception.
=head4 Examples
=head2 Locale, EBCDIC, Unicode and UTF-8
Some of the character classes have a somewhat different behaviour
-depending on the internal encoding of the source string, if the regular
-expression is marked as having Unicode semantics, the locale that is in
-effect, and if the program is running on an EBCDIC platform.
+depending on the internal encoding of the source string, whether the regular
+expression is marked as having Unicode semantics, whatever locale is in
+effect, and whether the program is running on an EBCDIC platform.
C<\w>, C<\d>, C<\s> and the POSIX character classes (and their
negations, including C<\W>, C<\D>, C<\S>) have this behaviour. (Since
For portability reasons, unless the C<"a"> modifier is specified,
it may be better to not use C<\w>, C<\d>, C<\s> or the POSIX character
classes and use the Unicode properties instead.
-That way you can control whether you want matching of just characters in
-the ASCII character set, or any Unicode characters.
-C<S<use feature "unicode_strings">> will allow seamless Unicode behavior
-no matter what the internal encodings are, but won't allow restricting
-to just the ASCII characters.
+
+That way you can control whether you want matching of characters in
+the ASCII character set alone, or whether to match Unicode characters.
+C<S<use feature "unicode_strings">> allows seamless Unicode behavior
+no matter the internal encodings, but won't allow restricting
+to ASCII characters only.
=head4 Examples
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