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diff --git a/Master/tlpkg/tlperl/lib/pods/perlrebackslash.pod b/Master/tlpkg/tlperl/lib/pods/perlrebackslash.pod deleted file mode 100644 index f81af0c6dd7..00000000000 --- a/Master/tlpkg/tlperl/lib/pods/perlrebackslash.pod +++ /dev/null @@ -1,661 +0,0 @@ -=head1 NAME - -perlrebackslash - Perl Regular Expression Backslash Sequences and Escapes - -=head1 DESCRIPTION - -The top level documentation about Perl regular expressions -is found in L<perlre>. - -This document describes all backslash and escape sequences. After -explaining the role of the backslash, it lists all the sequences that have -a special meaning in Perl regular expressions (in alphabetical order), -then describes each of them. - -Most sequences are described in detail in different documents; the primary -purpose of this document is to have a quick reference guide describing all -backslash and escape sequences. - -=head2 The backslash - -In a regular expression, the backslash can perform one of two tasks: -it either takes away the special meaning of the character following it -(for instance, C<\|> matches a vertical bar, it's not an alternation), -or it is the start of a backslash or escape sequence. - -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 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 issues a warning if you use such a -sequence. [1]. - -It is however guaranteed that backslash or escape sequences never have a -punctuation character following the backslash, not now, and not in a future -version of Perl 5. So it is safe to put a backslash in front of a non-word -character. - -Note that the backslash itself is special; if you want to match a backslash, -you have to escape the backslash with a backslash: C</\\/> matches a single -backslash. - -=over 4 - -=item [1] - -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 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>. - -=back - - -=head2 All the sequences and escapes - -Those not usable within a bracketed character class (like C<[\da-z]>) are marked -as C<Not in [].> - - \000 Octal escape sequence. See also \o{}. - \1 Absolute backreference. Not in []. - \a Alarm or bell. - \A Beginning of string. Not in []. - \b Word/non-word boundary. (Backspace in []). - \B Not a word/non-word boundary. Not in []. - \cX Control-X - \C Single octet, even under UTF-8. Not in []. - \d Character class for digits. - \D Character class for non-digits. - \e Escape character. - \E Turn off \Q, \L and \U processing. Not in []. - \f Form feed. - \F Foldcase till \E. Not in []. - \g{}, \g1 Named, absolute or relative backreference. Not in [] - \G Pos assertion. Not in []. - \h Character class for horizontal whitespace. - \H Character class for non horizontal whitespace. - \k{}, \k<>, \k'' Named backreference. Not in []. - \K Keep the stuff left of \K. Not in []. - \l Lowercase next character. Not in []. - \L Lowercase till \E. Not in []. - \n (Logical) newline character. - \N Any character but newline. Experimental. Not in []. - \N{} Named or numbered (Unicode) character or sequence. - \o{} Octal escape sequence. - \p{}, \pP Character with the given Unicode property. - \P{}, \PP Character without the given Unicode property. - \Q Quote (disable) pattern metacharacters till \E. Not - in []. - \r Return character. - \R Generic new line. Not in []. - \s Character class for whitespace. - \S Character class for non whitespace. - \t Tab character. - \u Titlecase next character. Not in []. - \U Uppercase till \E. Not in []. - \v Character class for vertical whitespace. - \V Character class for non vertical whitespace. - \w Character class for word characters. - \W Character class for non-word characters. - \x{}, \x00 Hexadecimal escape sequence. - \X Unicode "extended grapheme cluster". Not in []. - \z End of string. Not in []. - \Z End of string. Not in []. - -=head2 Character Escapes - -=head3 Fixed characters - -A handful of characters have a dedicated I<character escape>. The following -table shows them, along with their ASCII code points (in decimal and hex), -their ASCII name, the control escape on ASCII platforms and a short -description. (For EBCDIC platforms, see L<perlebcdic/OPERATOR DIFFERENCES>.) - - Seq. Code Point ASCII Cntrl Description. - Dec Hex - \a 7 07 BEL \cG alarm or bell - \b 8 08 BS \cH backspace [1] - \e 27 1B ESC \c[ escape character - \f 12 0C FF \cL form feed - \n 10 0A LF \cJ line feed [2] - \r 13 0D CR \cM carriage return - \t 9 09 TAB \cI tab - -=over 4 - -=item [1] - -C<\b> is the backspace character only inside a character class. Outside a -character class, C<\b> is a word/non-word boundary. - -=item [2] - -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 - -=head4 Example - - $str =~ /\t/; # Matches if $str contains a (horizontal) tab. - -=head3 Control characters - -C<\c> is used to denote a control character; the character following C<\c> -determines the value of the construct. For example the value of C<\cA> is -C<chr(1)>, and the value of C<\cb> is C<chr(2)>, etc. -The gory details are in L<perlop/"Regexp Quote-Like Operators">. A complete -list of what C<chr(1)>, etc. means for ASCII and EBCDIC platforms is in -L<perlebcdic/OPERATOR DIFFERENCES>. - -Note that C<\c\> alone at the end of a regular expression (or doubled-quoted -string) is not valid. The backslash must be followed by another character. -That is, C<\c\I<X>> means C<chr(28) . 'I<X>'> for all characters I<X>. - -To write platform-independent code, you must use C<\N{I<NAME>}> instead, like -C<\N{ESCAPE}> or C<\N{U+001B}>, see L<charnames>. - -Mnemonic: I<c>ontrol character. - -=head4 Example - - $str =~ /\cK/; # Matches if $str contains a vertical tab (control-K). - -=head3 Named or numbered characters and character sequences - -Unicode characters have a Unicode name and numeric code point (ordinal) -value. Use the -C<\N{}> construct to specify a character by either of these values. -Certain sequences of characters also have names. - -To specify by name, the name of the character or character sequence goes -between the curly braces. - -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 -code point 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<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 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 - - $str =~ /\N{THAI CHARACTER SO SO}/; # Matches the Thai SO SO character - - use charnames 'Cyrillic'; # Loads Cyrillic names. - $str =~ /\N{ZHE}\N{KA}/; # Match "ZHE" followed by "KA". - -=head3 Octal escapes - -There are two forms of octal escapes. Each is used to specify a character by -its code point specified in octal notation. - -One form, available starting in Perl 5.14 looks like C<\o{...}>, where the dots -represent one or more octal digits. It can be used for any Unicode character. - -It was introduced to avoid the potential problems with the other form, -available in all Perls. That form consists of a backslash followed by three -octal digits. One problem with this form is that it can look exactly like an -old-style backreference (see -L</Disambiguation rules between old-style octal escapes and backreferences> -below.) You can avoid this by making the first of the three digits always a -zero, but that makes \077 the largest code point specifiable. - -In some contexts, a backslash followed by two or even one octal digits may be -interpreted as an octal escape, sometimes with a warning, and because of some -bugs, sometimes with surprising results. Also, if you are creating a regex -out of smaller snippets concatenated together, and you use fewer than three -digits, the beginning of one snippet may be interpreted as adding digits to the -ending of the snippet before it. See L</Absolute referencing> for more -discussion and examples of the snippet problem. - -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 -safe to use for code points through \077 when you use exactly three digits to -specify them. - -Mnemonic: I<0>ctal or I<o>ctal. - -=head4 Examples (assuming an ASCII platform) - - $str = "Perl"; - $str =~ /\o{120}/; # Match, "\120" is "P". - $str =~ /\120/; # Same. - $str =~ /\o{120}+/; # Match, "\120" is "P", it's repeated at least once - $str =~ /\120+/; # Same. - $str =~ /P\053/; # No match, "\053" is "+" and taken literally. - /\o{23073}/ # Black foreground, white background smiling face. - /\o{4801234567}/ # Raises a warning, and yields chr(4) - -=head4 Disambiguation rules between old-style octal escapes and backreferences - -Octal escapes of the C<\000> form outside of bracketed character classes -potentially clash with old-style backreferences. (see L</Absolute referencing> -below). They both consist of a backslash followed by numbers. So Perl has to -use heuristics to determine whether it is a backreference or an octal escape. -Perl uses the following rules to disambiguate: - -=over 4 - -=item 1 - -If the backslash is followed by a single digit, it's a backreference. - -=item 2 - -If the first digit following the backslash is a 0, it's an octal escape. - -=item 3 - -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"; - $pat .= ")" x 999; - /^($pat)\1000$/; # Matches 'aa'; there are 1000 capture groups. - /^$pat\1000$/; # Matches 'a@0'; there are 999 capture groups - # and \1000 is seen as \100 (a '@') and a '0' - -=back - -You can force a backreference interpretation always by using the C<\g{...}> -form. You can the force an octal interpretation always by using the C<\o{...}> -form, or for numbers up through \077 (= 63 decimal), by using three digits, -beginning with a "0". - -=head3 Hexadecimal escapes - -Like octal escapes, there are two forms of hexadecimal escapes, but both start -with the same thing, C<\x>. This is followed by either exactly two hexadecimal -digits forming a number, or a hexadecimal number of arbitrary length surrounded -by curly braces. The hexadecimal number is the code point of the character you -want to express. - -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. - -=head4 Examples (assuming an ASCII platform) - - $str = "Perl"; - $str =~ /\x50/; # Match, "\x50" is "P". - $str =~ /\x50+/; # Match, "\x50" is "P", it is repeated at least once - $str =~ /P\x2B/; # No match, "\x2B" is "+" and taken literally. - - /\x{2603}\x{2602}/ # Snowman with an umbrella. - # The Unicode character 2603 is a snowman, - # the Unicode character 2602 is an umbrella. - /\x{263B}/ # Black smiling face. - /\x{263b}/ # Same, the hex digits A - F are case insensitive. - -=head2 Modifiers - -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 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>, whichever comes first. They provide functionality similar to what -the functions C<lc> and C<uc> provide. - -C<\Q> is used to quote (disable) pattern metacharacters, up to the next -C<\E> or the end of the pattern. C<\Q> adds a backslash to any character -that could have special meaning to Perl. In the ASCII range, it quotes -every character that isn't a letter, digit, or underscore. See -L<perlfunc/quotemeta> for details on what gets quoted for non-ASCII -code points. Using this ensures that any character between C<\Q> and -C<\E> will be matched literally, not interpreted as a metacharacter by -the regex engine. - -C<\F> can be used to casefold all characters following, up to the next C<\E> -or the end of the pattern. It provides the functionality similar to -the C<fc> function. - -Mnemonic: I<L>owercase, I<U>ppercase, I<F>old-case, I<Q>uotemeta, I<E>nd. - -=head4 Examples - - $sid = "sid"; - $greg = "GrEg"; - $miranda = "(Miranda)"; - $str =~ /\u$sid/; # Matches 'Sid' - $str =~ /\L$greg/; # Matches 'greg' - $str =~ /\Q$miranda\E/; # Matches '(Miranda)', as if the pattern - # had been written as /\(Miranda\)/ - -=head2 Character classes - -Perl regular expressions have a large range of character classes. Some of -the character classes are written as a backslash sequence. We will briefly -discuss those here; full details of character classes can be found in -L<perlrecharclass>. - -C<\w> is a character class that matches any single I<word> character -(letters, digits, Unicode marks, and connector punctuation (like the -underscore)). C<\d> is a character class that matches any decimal -digit, while the character class C<\s> matches any whitespace character. -New in perl 5.10.0 are the classes C<\h> and C<\v> which match horizontal -and vertical whitespace characters. - -The exact set of characters matched by C<\d>, C<\s>, and C<\w> varies -depending on various pragma and regular expression modifiers. It is -possible to restrict the match to the ASCII range by using the C</a> -regular expression modifier. See L<perlrecharclass>. - -The uppercase variants (C<\W>, C<\D>, C<\S>, C<\H>, and C<\V>) are -character classes that match, respectively, any character that isn't a -word character, digit, whitespace, horizontal whitespace, or vertical -whitespace. - -Mnemonics: I<w>ord, I<d>igit, I<s>pace, I<h>orizontal, I<v>ertical. - -=head3 Unicode classes - -C<\pP> (where C<P> is a single letter) and C<\p{Property}> are used to -match a character that matches the given Unicode property; properties -include things like "letter", or "thai character". Capitalizing the -sequence to C<\PP> and C<\P{Property}> make the sequence match a character -that doesn't match the given Unicode property. For more details, see -L<perlrecharclass/Backslash sequences> and -L<perlunicode/Unicode Character Properties>. - -Mnemonic: I<p>roperty. - -=head2 Referencing - -If capturing parenthesis are used in a regular expression, we can refer -to the part of the source string that was matched, and match exactly the -same thing. There are three ways of referring to such I<backreference>: -absolutely, relatively, and by name. - -=for later add link to perlrecapture - -=head3 Absolute referencing - -Either C<\gI<N>> (starting in Perl 5.10.0), or C<\I<N>> (old-style) where I<N> -is a positive (unsigned) decimal number of any length is an absolute reference -to a capturing group. - -I<N> refers to the Nth set of parentheses, so C<\gI<N>> refers to whatever has -been matched by that set of parentheses. Thus C<\g1> refers to the first -capture group in the regex. - -The C<\gI<N>> form can be equivalently written as C<\g{I<N>}> -which avoids ambiguity when building a regex by concatenating shorter -strings. Otherwise if you had a regex C<qr/$a$b/>, and C<$a> contained -C<"\g1">, and C<$b> contained C<"37">, you would get C</\g137/> which is -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> 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. - -=head4 Examples - - /(\w+) \g1/; # Finds a duplicated word, (e.g. "cat cat"). - /(\w+) \1/; # Same thing; written old-style - /(.)(.)\g2\g1/; # Match a four letter palindrome (e.g. "ABBA"). - - -=head3 Relative referencing - -C<\g-I<N>> (starting in Perl 5.10.0) is used for relative addressing. (It can -be written as C<\g{-I<N>>.) It refers to the I<N>th group before the -C<\g{-I<N>}>. - -The big advantage of this form is that it makes it much easier to write -patterns with references that can be interpolated in larger patterns, -even if the larger pattern also contains capture groups. - -=head4 Examples - - /(A) # Group 1 - ( # Group 2 - (B) # Group 3 - \g{-1} # Refers to group 3 (B) - \g{-3} # Refers to group 1 (A) - ) - /x; # Matches "ABBA". - - my $qr = qr /(.)(.)\g{-2}\g{-1}/; # Matches 'abab', 'cdcd', etc. - /$qr$qr/ # Matches 'ababcdcd'. - -=head3 Named referencing - -C<\g{I<name>}> (starting in Perl 5.10.0) can be used to back refer to a -named capture group, dispensing completely with having to think about capture -buffer positions. - -To be compatible with .Net regular expressions, C<\g{name}> may also be -written as C<\k{name}>, C<< \k<name> >> or C<\k'name'>. - -To prevent any ambiguity, I<name> must not start with a digit nor contain a -hyphen. - -=head4 Examples - - /(?<word>\w+) \g{word}/ # Finds duplicated word, (e.g. "cat cat") - /(?<word>\w+) \k{word}/ # Same. - /(?<word>\w+) \k<word>/ # Same. - /(?<letter1>.)(?<letter2>.)\g{letter2}\g{letter1}/ - # Match a four letter palindrome (e.g. "ABBA") - -=head2 Assertions - -Assertions are conditions that have to be true; they don't actually -match parts of the substring. There are six assertions that are written as -backslash sequences. - -=over 4 - -=item \A - -C<\A> only matches at the beginning of the string. If the C</m> modifier -isn't used, then C</\A/> is equivalent to C</^/>. However, if the C</m> -modifier is used, then C</^/> matches internal newlines, but the meaning -of C</\A/> isn't changed by the C</m> modifier. C<\A> matches at the beginning -of the string regardless whether the C</m> modifier is used. - -=item \z, \Z - -C<\z> and C<\Z> match at the end of the string. If the C</m> modifier isn't -used, then C</\Z/> is equivalent to C</$/>; that is, it matches at the -end of the string, or 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 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 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 on that string ended, -or the beginning of that string if there was no previous match. - -=for later add link to perlremodifiers - -Mnemonic: I<G>lobal. - -=item \b, \B - -C<\b> matches at any place between a word and a non-word character; C<\B> -matches at any place between characters where C<\b> doesn't match. C<\b> -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. - -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. - -=back - -=head4 Examples - - "cat" =~ /\Acat/; # Match. - "cat" =~ /cat\Z/; # Match. - "cat\n" =~ /cat\Z/; # Match. - "cat\n" =~ /cat\z/; # No match. - - "cat" =~ /\bcat\b/; # Matches. - "cats" =~ /\bcat\b/; # No match. - "cat" =~ /\bcat\B/; # No match. - "cats" =~ /\bcat\B/; # Match. - - while ("cat dog" =~ /(\w+)/g) { - print $1; # Prints 'catdog' - } - while ("cat dog" =~ /\G(\w+)/g) { - print $1; # Prints 'cat' - } - -=head2 Misc - -Here we document the backslash sequences that don't fall in one of the -categories above. These are: - -=over 4 - -=item \C - -C<\C> always matches a single octet, even if the source string is encoded -in UTF-8 format, and the character to be matched is a multi-octet character. -C<\C> was introduced in perl 5.6. This is very dangerous, because it violates -the logical character abstraction and can cause UTF-8 sequences to become malformed. - -Mnemonic: oI<C>tet. - -=item \K - -This appeared in perl 5.10.0. Anything matched left of C<\K> is -not included in C<$&>, 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/${1}REPL/x> or C<s/(?<=PAT1) PAT2/REPL/x>. - -Mnemonic: I<K>eep. - -=item \N - -This is an experimental feature new to perl 5.12.0. It matches any character -that is B<not> a newline. It is a short-hand for writing C<[^\n]>, and is -identical to the C<.> metasymbol, except under the C</s> flag, which changes -the meaning of C<.>, but not C<\N>. - -Note that C<\N{...}> can mean a -L<named or numbered character -|/Named or numbered characters and character sequences>. - -Mnemonic: Complement of I<\n>. - -=item \R -X<\R> - -C<\R> matches a I<generic newline>; that is, anything considered a -linebreak sequence by Unicode. This includes all characters matched by -C<\v> (vertical whitespace), and the multi character sequence C<"\x0D\x0A"> -(carriage return followed by a line feed, sometimes called the network -newline; it's the end of line sequence used in Microsoft text files opened -in binary mode). C<\R> is equivalent to C<< (?>\x0D\x0A|\v) >>. (The -reason it doesn't backtrack is that the sequence is considered -inseparable. That means that - - "\x0D\x0A" =~ /^\R\x0A$/ # No match - -fails, because the C<\R> matches the entire string, and won't backtrack -to match just the C<"\x0D">.) 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. - -Note that this does not respect any locale that might be in effect; it -matches according to the platform's native character set. - -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 its notation. - -=item \X -X<\X> - -This matches a Unicode I<extended grapheme cluster>. - -C<\X> matches quite well what normal (non-Unicode-programmer) usage -would consider a single character. As an example, consider a G with some sort -of diacritic mark, such as an arrow. There is no such single character in -Unicode, but one can be composed by using a G followed by a Unicode "COMBINING -UPWARDS ARROW BELOW", and would be displayed by Unicode-aware software as if it -were a single character. - -Mnemonic: eI<X>tended Unicode character. - -=back - -=head4 Examples - - "\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' - $str =~ s/(.)\K\g1//g; # Delete duplicated characters. - - "\n" =~ /^\R$/; # Match, \n is a generic newline. - "\r" =~ /^\R$/; # Match, \r is a generic newline. - "\r\n" =~ /^\R$/; # Match, \r\n is a generic newline. - - "P\x{307}" =~ /^\X$/ # \X matches a P with a dot above. - -=cut |