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Text::Balanced(3pm)    Perl Programmers Reference Guide    Text::Balanced(3pm)




NAME

       Text::Balanced - Extract delimited text sequences from strings.


SYNOPSIS

           use Text::Balanced qw (
               extract_delimited
               extract_bracketed
               extract_quotelike
               extract_codeblock
               extract_variable
               extract_tagged
               extract_multiple
               gen_delimited_pat
               gen_extract_tagged
           );

           # Extract the initial substring of $text that is delimited by
           # two (unescaped) instances of the first character in $delim.

           ($extracted, $remainder) = extract_delimited($text,$delim);

           # Extract the initial substring of $text that is bracketed
           # with a delimiter(s) specified by $delim (where the string
           # in $delim contains one or more of '(){}[]<>').

           ($extracted, $remainder) = extract_bracketed($text,$delim);

           # Extract the initial substring of $text that is bounded by
           # an XML tag.

           ($extracted, $remainder) = extract_tagged($text);

           # Extract the initial substring of $text that is bounded by
           # a C<BEGIN>...C<END> pair. Don't allow nested C<BEGIN> tags

           ($extracted, $remainder) =
               extract_tagged($text,"BEGIN","END",undef,{bad=>["BEGIN"]});

           # Extract the initial substring of $text that represents a
           # Perl "quote or quote-like operation"

           ($extracted, $remainder) = extract_quotelike($text);

           # Extract the initial substring of $text that represents a block
           # of Perl code, bracketed by any of character(s) specified by $delim
           # (where the string $delim contains one or more of '(){}[]<>').

           ($extracted, $remainder) = extract_codeblock($text,$delim);

           # Extract the initial substrings of $text that would be extracted by
           # one or more sequential applications of the specified functions
           # or regular expressions

           @extracted = extract_multiple($text,
                                         [ \&extract_bracketed,
                                           \&extract_quotelike,
                                           \&some_other_extractor_sub,
                                           qr/[xyz]*/,
                                           'literal',
                                         ]);

           # Create a string representing an optimized pattern (a la Friedl)
           # that matches a substring delimited by any of the specified characters
           # (in this case: any type of quote or a slash)

           $patstring = gen_delimited_pat(q{'"`/});

           # Generate a reference to an anonymous sub that is just like extract_tagged
           # but pre-compiled and optimized for a specific pair of tags, and
           # consequently much faster (i.e. 3 times faster). It uses qr// for better
           # performance on repeated calls.

           $extract_head = gen_extract_tagged('<HEAD>','</HEAD>');
           ($extracted, $remainder) = $extract_head->($text);


DESCRIPTION

       The various "extract_..." subroutines may be used to extract a
       delimited substring, possibly after skipping a specified prefix string.
       By default, that prefix is optional whitespace ("/\s*/"), but you can
       change it to whatever you wish (see below).

       The substring to be extracted must appear at the current "pos" location
       of the string's variable (or at index zero, if no "pos" position is
       defined).  In other words, the "extract_..." subroutines don't extract
       the first occurrence of a substring anywhere in a string (like an
       unanchored regex would). Rather, they extract an occurrence of the
       substring appearing immediately at the current matching position in the
       string (like a "\G"-anchored regex would).

   General Behaviour in List Contexts
       In a list context, all the subroutines return a list, the first three
       elements of which are always:

       [0] The extracted string, including the specified delimiters.  If the
           extraction fails "undef" is returned.

       [1] The remainder of the input string (i.e. the characters after the
           extracted string). On failure, the entire string is returned.

       [2] The skipped prefix (i.e. the characters before the extracted
           string).  On failure, "undef" is returned.

       Note that in a list context, the contents of the original input text
       (the first argument) are not modified in any way.

       However, if the input text was passed in a variable, that variable's
       "pos" value is updated to point at the first character after the
       extracted text. That means that in a list context the various
       subroutines can be used much like regular expressions. For example:

           while ( $next = (extract_quotelike($text))[0] )
           {
               # process next quote-like (in $next)
           }

   General Behaviour in Scalar and Void Contexts
       In a scalar context, the extracted string is returned, having first
       been removed from the input text. Thus, the following code also
       processes each quote-like operation, but actually removes them from
       $text:

           while ( $next = extract_quotelike($text) )
           {
               # process next quote-like (in $next)
           }

       Note that if the input text is a read-only string (i.e. a literal), no
       attempt is made to remove the extracted text.

       In a void context the behaviour of the extraction subroutines is
       exactly the same as in a scalar context, except (of course) that the
       extracted substring is not returned.

   A Note About Prefixes
       Prefix patterns are matched without any trailing modifiers ("/gimsox"
       etc.)  This can bite you if you're expecting a prefix specification
       like '.*?(?=<H1>)' to skip everything up to the first <H1> tag. Such a
       prefix pattern will only succeed if the <H1> tag is on the current
       line, since . normally doesn't match newlines.

       To overcome this limitation, you need to turn on /s matching within the
       prefix pattern, using the "(?s)" directive: '(?s).*?(?=<H1>)'

   Functions
       "extract_delimited"
           The "extract_delimited" function formalizes the common idiom of
           extracting a single-character-delimited substring from the start of
           a string. For example, to extract a single-quote delimited string,
           the following code is typically used:

               ($remainder = $text) =~ s/\A('(\\.|[^'])*')//s;
               $extracted = $1;

           but with "extract_delimited" it can be simplified to:

               ($extracted,$remainder) = extract_delimited($text, "'");

           "extract_delimited" takes up to four scalars (the input text, the
           delimiters, a prefix pattern to be skipped, and any escape
           characters) and extracts the initial substring of the text that is
           appropriately delimited. If the delimiter string has multiple
           characters, the first one encountered in the text is taken to
           delimit the substring.  The third argument specifies a prefix
           pattern that is to be skipped (but must be present!) before the
           substring is extracted.  The final argument specifies the escape
           character to be used for each delimiter.

           All arguments are optional. If the escape characters are not
           specified, every delimiter is escaped with a backslash ("\").  If
           the prefix is not specified, the pattern '\s*' - optional
           whitespace - is used. If the delimiter set is also not specified,
           the set "/["'`]/" is used. If the text to be processed is not
           specified either, $_ is used.

           In list context, "extract_delimited" returns a array of three
           elements, the extracted substring (including the surrounding
           delimiters), the remainder of the text, and the skipped prefix (if
           any). If a suitable delimited substring is not found, the first
           element of the array is the empty string, the second is the
           complete original text, and the prefix returned in the third
           element is an empty string.

           In a scalar context, just the extracted substring is returned. In a
           void context, the extracted substring (and any prefix) are simply
           removed from the beginning of the first argument.

           Examples:

               # Remove a single-quoted substring from the very beginning of $text:

                   $substring = extract_delimited($text, "'", '');

               # Remove a single-quoted Pascalish substring (i.e. one in which
               # doubling the quote character escapes it) from the very
               # beginning of $text:

                   $substring = extract_delimited($text, "'", '', "'");

               # Extract a single- or double- quoted substring from the
               # beginning of $text, optionally after some whitespace
               # (note the list context to protect $text from modification):

                   ($substring) = extract_delimited $text, q{"'};

               # Delete the substring delimited by the first '/' in $text:

                   $text = join '', (extract_delimited($text,'/','[^/]*')[2,1];

           Note that this last example is not the same as deleting the first
           quote-like pattern. For instance, if $text contained the string:

               "if ('./cmd' =~ m/$UNIXCMD/s) { $cmd = $1; }"

           then after the deletion it would contain:

               "if ('.$UNIXCMD/s) { $cmd = $1; }"

           not:

               "if ('./cmd' =~ ms) { $cmd = $1; }"

           See "extract_quotelike" for a (partial) solution to this problem.

       "extract_bracketed"
           Like "extract_delimited", the "extract_bracketed" function takes up
           to three optional scalar arguments: a string to extract from, a
           delimiter specifier, and a prefix pattern. As before, a missing
           prefix defaults to optional whitespace and a missing text defaults
           to $_. However, a missing delimiter specifier defaults to
           '{}()[]<>' (see below).

           "extract_bracketed" extracts a balanced-bracket-delimited substring
           (using any one (or more) of the user-specified delimiter brackets:
           '(..)', '{..}', '[..]', or '<..>'). Optionally it will also respect
           quoted unbalanced brackets (see below).

           A "delimiter bracket" is a bracket in list of delimiters passed as
           "extract_bracketed"'s second argument. Delimiter brackets are
           specified by giving either the left or right (or both!) versions of
           the required bracket(s). Note that the order in which two or more
           delimiter brackets are specified is not significant.

           A "balanced-bracket-delimited substring" is a substring bounded by
           matched brackets, such that any other (left or right) delimiter
           bracket within the substring is also matched by an opposite (right
           or left) delimiter bracket at the same level of nesting. Any type
           of bracket not in the delimiter list is treated as an ordinary
           character.

           In other words, each type of bracket specified as a delimiter must
           be balanced and correctly nested within the substring, and any
           other kind of ("non-delimiter") bracket in the substring is
           ignored.

           For example, given the string:

               $text = "{ an '[irregularly :-(] {} parenthesized >:-)' string }";

           then a call to "extract_bracketed" in a list context:

               @result = extract_bracketed( $text, '{}' );

           would return:

               ( "{ an '[irregularly :-(] {} parenthesized >:-)' string }" , "" , "" )

           since both sets of '{..}' brackets are properly nested and evenly
           balanced.  (In a scalar context just the first element of the array
           would be returned. In a void context, $text would be replaced by an
           empty string.)

           Likewise the call in:

               @result = extract_bracketed( $text, '{[' );

           would return the same result, since all sets of both types of
           specified delimiter brackets are correctly nested and balanced.

           However, the call in:

               @result = extract_bracketed( $text, '{([<' );

           would fail, returning:

               ( undef , "{ an '[irregularly :-(] {} parenthesized >:-)' string }"  );

           because the embedded pairs of '(..)'s and '[..]'s are "cross-
           nested" and the embedded '>' is unbalanced. (In a scalar context,
           this call would return an empty string. In a void context, $text
           would be unchanged.)

           Note that the embedded single-quotes in the string don't help in
           this case, since they have not been specified as acceptable
           delimiters and are therefore treated as non-delimiter characters
           (and ignored).

           However, if a particular species of quote character is included in
           the delimiter specification, then that type of quote will be
           correctly handled.  for example, if $text is:

               $text = '<A HREF=">>>>">link</A>';

           then

               @result = extract_bracketed( $text, '<">' );

           returns:

               ( '<A HREF=">>>>">', 'link</A>', "" )

           as expected. Without the specification of """ as an embedded
           quoter:

               @result = extract_bracketed( $text, '<>' );

           the result would be:

               ( '<A HREF=">', '>>>">link</A>', "" )

           In addition to the quote delimiters "'", """, and "`", full Perl
           quote-like quoting (i.e. q{string}, qq{string}, etc) can be
           specified by including the letter 'q' as a delimiter. Hence:

               @result = extract_bracketed( $text, '<q>' );

           would correctly match something like this:

               $text = '<leftop: conj /and/ conj>';

           See also: "extract_quotelike" and "extract_codeblock".

       "extract_variable"
           "extract_variable" extracts any valid Perl variable or variable-
           involved expression, including scalars, arrays, hashes, array
           accesses, hash look-ups, method calls through objects, subroutine
           calls through subroutine references, etc.

           The subroutine takes up to two optional arguments:

           1.  A string to be processed ($_ if the string is omitted or
               "undef")

           2.  A string specifying a pattern to be matched as a prefix (which
               is to be skipped). If omitted, optional whitespace is skipped.

           On success in a list context, an array of 3 elements is returned.
           The elements are:

           [0] the extracted variable, or variablish expression

           [1] the remainder of the input text,

           [2] the prefix substring (if any),

           On failure, all of these values (except the remaining text) are
           "undef".

           In a scalar context, "extract_variable" returns just the complete
           substring that matched a variablish expression. "undef" is returned
           on failure. In addition, the original input text has the returned
           substring (and any prefix) removed from it.

           In a void context, the input text just has the matched substring
           (and any specified prefix) removed.

       "extract_tagged"
           "extract_tagged" extracts and segments text between (balanced)
           specified tags.

           The subroutine takes up to five optional arguments:

           1.  A string to be processed ($_ if the string is omitted or
               "undef")

           2.  A string specifying a pattern to be matched as the opening tag.
               If the pattern string is omitted (or "undef") then a pattern
               that matches any standard XML tag is used.

           3.  A string specifying a pattern to be matched at the closing tag.
               If the pattern string is omitted (or "undef") then the closing
               tag is constructed by inserting a "/" after any leading bracket
               characters in the actual opening tag that was matched (not the
               pattern that matched the tag). For example, if the opening tag
               pattern is specified as '{{\w+}}' and actually matched the
               opening tag "{{DATA}}", then the constructed closing tag would
               be "{{/DATA}}".

           4.  A string specifying a pattern to be matched as a prefix (which
               is to be skipped). If omitted, optional whitespace is skipped.

           5.  A hash reference containing various parsing options (see below)

           The various options that can be specified are:

           "reject => $listref"
               The list reference contains one or more strings specifying
               patterns that must not appear within the tagged text.

               For example, to extract an HTML link (which should not contain
               nested links) use:

                       extract_tagged($text, '<A>', '</A>', undef, {reject => ['<A>']} );

           "ignore => $listref"
               The list reference contains one or more strings specifying
               patterns that are not to be treated as nested tags within the
               tagged text (even if they would match the start tag pattern).

               For example, to extract an arbitrary XML tag, but ignore
               "empty" elements:

                       extract_tagged($text, undef, undef, undef, {ignore => ['<[^>]*/>']} );

               (also see "gen_delimited_pat" below).

           "fail => $str"
               The "fail" option indicates the action to be taken if a
               matching end tag is not encountered (i.e. before the end of the
               string or some "reject" pattern matches). By default, a failure
               to match a closing tag causes "extract_tagged" to immediately
               fail.

               However, if the string value associated with <reject> is "MAX",
               then "extract_tagged" returns the complete text up to the point
               of failure.  If the string is "PARA", "extract_tagged" returns
               only the first paragraph after the tag (up to the first line
               that is either empty or contains only whitespace characters).
               If the string is "", the default behaviour (i.e. failure) is
               reinstated.

               For example, suppose the start tag "/para" introduces a
               paragraph, which then continues until the next "/endpara" tag
               or until another "/para" tag is encountered:

                       $text = "/para line 1\n\nline 3\n/para line 4";

                       extract_tagged($text, '/para', '/endpara', undef,
                                               {reject => '/para', fail => MAX );

                       # EXTRACTED: "/para line 1\n\nline 3\n"

               Suppose instead, that if no matching "/endpara" tag is found,
               the "/para" tag refers only to the immediately following
               paragraph:

                       $text = "/para line 1\n\nline 3\n/para line 4";

                       extract_tagged($text, '/para', '/endpara', undef,
                                       {reject => '/para', fail => MAX );

                       # EXTRACTED: "/para line 1\n"

               Note that the specified "fail" behaviour applies to nested tags
               as well.

           On success in a list context, an array of 6 elements is returned.
           The elements are:

           [0] the extracted tagged substring (including the outermost tags),

           [1] the remainder of the input text,

           [2] the prefix substring (if any),

           [3] the opening tag

           [4] the text between the opening and closing tags

           [5] the closing tag (or "" if no closing tag was found)

           On failure, all of these values (except the remaining text) are
           "undef".

           In a scalar context, "extract_tagged" returns just the complete
           substring that matched a tagged text (including the start and end
           tags). "undef" is returned on failure. In addition, the original
           input text has the returned substring (and any prefix) removed from
           it.

           In a void context, the input text just has the matched substring
           (and any specified prefix) removed.

       "gen_extract_tagged"
           "gen_extract_tagged" generates a new anonymous subroutine which
           extracts text between (balanced) specified tags. In other words, it
           generates a function identical in function to "extract_tagged".

           The difference between "extract_tagged" and the anonymous
           subroutines generated by "gen_extract_tagged", is that those
           generated subroutines:

           o   do not have to reparse tag specification or parsing options
               every time they are called (whereas "extract_tagged" has to
               effectively rebuild its tag parser on every call);

           o   make use of the new qr// construct to pre-compile the regexes
               they use (whereas "extract_tagged" uses standard string
               variable interpolation to create tag-matching patterns).

           The subroutine takes up to four optional arguments (the same set as
           "extract_tagged" except for the string to be processed). It returns
           a reference to a subroutine which in turn takes a single argument
           (the text to be extracted from).

           In other words, the implementation of "extract_tagged" is exactly
           equivalent to:

                   sub extract_tagged
                   {
                           my $text = shift;
                           $extractor = gen_extract_tagged(@_);
                           return $extractor->($text);
                   }

           (although "extract_tagged" is not currently implemented that way).

           Using "gen_extract_tagged" to create extraction functions for
           specific tags is a good idea if those functions are going to be
           called more than once, since their performance is typically twice
           as good as the more general-purpose "extract_tagged".

       "extract_quotelike"
           "extract_quotelike" attempts to recognize, extract, and segment any
           one of the various Perl quotes and quotelike operators (see
           perlop(3)) Nested backslashed delimiters, embedded balanced bracket
           delimiters (for the quotelike operators), and trailing modifiers
           are all caught. For example, in:

                   extract_quotelike 'q # an octothorpe: \# (not the end of the q!) #'

                   extract_quotelike '  "You said, \"Use sed\"."  '

                   extract_quotelike ' s{([A-Z]{1,8}\.[A-Z]{3})} /\L$1\E/; '

                   extract_quotelike ' tr/\\\/\\\\/\\\//ds; '

           the full Perl quotelike operations are all extracted correctly.

           Note too that, when using the /x modifier on a regex, any comment
           containing the current pattern delimiter will cause the regex to be
           immediately terminated. In other words:

                   'm /
                           (?i)            # CASE INSENSITIVE
                           [a-z_]          # LEADING ALPHABETIC/UNDERSCORE
                           [a-z0-9]*       # FOLLOWED BY ANY NUMBER OF ALPHANUMERICS
                      /x'

           will be extracted as if it were:

                   'm /
                           (?i)            # CASE INSENSITIVE
                           [a-z_]          # LEADING ALPHABETIC/'

           This behaviour is identical to that of the actual compiler.

           "extract_quotelike" takes two arguments: the text to be processed
           and a prefix to be matched at the very beginning of the text. If no
           prefix is specified, optional whitespace is the default. If no text
           is given, $_ is used.

           In a list context, an array of 11 elements is returned. The
           elements are:

           [0] the extracted quotelike substring (including trailing
               modifiers),

           [1] the remainder of the input text,

           [2] the prefix substring (if any),

           [3] the name of the quotelike operator (if any),

           [4] the left delimiter of the first block of the operation,

           [5] the text of the first block of the operation (that is, the
               contents of a quote, the regex of a match or substitution or
               the target list of a translation),

           [6] the right delimiter of the first block of the operation,

           [7] the left delimiter of the second block of the operation (that
               is, if it is a "s", "tr", or "y"),

           [8] the text of the second block of the operation (that is, the
               replacement of a substitution or the translation list of a
               translation),

           [9] the right delimiter of the second block of the operation (if
               any),

           [10]
               the trailing modifiers on the operation (if any).

           For each of the fields marked "(if any)" the default value on
           success is an empty string.  On failure, all of these values
           (except the remaining text) are "undef".

           In a scalar context, "extract_quotelike" returns just the complete
           substring that matched a quotelike operation (or "undef" on
           failure). In a scalar or void context, the input text has the same
           substring (and any specified prefix) removed.

           Examples:

                   # Remove the first quotelike literal that appears in text

                           $quotelike = extract_quotelike($text,'.*?');

                   # Replace one or more leading whitespace-separated quotelike
                   # literals in $_ with "<QLL>"

                           do { $_ = join '<QLL>', (extract_quotelike)[2,1] } until $@;


                   # Isolate the search pattern in a quotelike operation from $text

                           ($op,$pat) = (extract_quotelike $text)[3,5];
                           if ($op =~ /[ms]/)
                           {
                                   print "search pattern: $pat\n";
                           }
                           else
                           {
                                   print "$op is not a pattern matching operation\n";
                           }

       "extract_quotelike"
           "extract_quotelike" can successfully extract "here documents" from
           an input string, but with an important caveat in list contexts.

           Unlike other types of quote-like literals, a here document is
           rarely a contiguous substring. For example, a typical piece of code
           using here document might look like this:

                   <<'EOMSG' || die;
                   This is the message.
                   EOMSG
                   exit;

           Given this as an input string in a scalar context,
           "extract_quotelike" would correctly return the string
           "<<'EOMSG'\nThis is the message.\nEOMSG", leaving the string " ||
           die;\nexit;" in the original variable. In other words, the two
           separate pieces of the here document are successfully extracted and
           concatenated.

           In a list context, "extract_quotelike" would return the list

           [0] "<<'EOMSG'\nThis is the message.\nEOMSG\n" (i.e. the full
               extracted here document, including fore and aft delimiters),

           [1] " || die;\nexit;" (i.e. the remainder of the input text,
               concatenated),

           [2] "" (i.e. the prefix substring -- trivial in this case),

           [3] "<<" (i.e. the "name" of the quotelike operator)

           [4] "'EOMSG'" (i.e. the left delimiter of the here document,
               including any quotes),

           [5] "This is the message.\n" (i.e. the text of the here document),

           [6] "EOMSG" (i.e. the right delimiter of the here document),

           [7..10]
               "" (a here document has no second left delimiter, second text,
               second right delimiter, or trailing modifiers).

           However, the matching position of the input variable would be set
           to "exit;" (i.e. after the closing delimiter of the here document),
           which would cause the earlier " || die;\nexit;" to be skipped in
           any sequence of code fragment extractions.

           To avoid this problem, when it encounters a here document whilst
           extracting from a modifiable string, "extract_quotelike" silently
           rearranges the string to an equivalent piece of Perl:

                   <<'EOMSG'
                   This is the message.
                   EOMSG
                   || die;
                   exit;

           in which the here document is contiguous. It still leaves the
           matching position after the here document, but now the rest of the
           line on which the here document starts is not skipped.

           To prevent <extract_quotelike> from mucking about with the input in
           this way (this is the only case where a list-context
           "extract_quotelike" does so), you can pass the input variable as an
           interpolated literal:

                   $quotelike = extract_quotelike("$var");

       "extract_codeblock"
           "extract_codeblock" attempts to recognize and extract a balanced
           bracket delimited substring that may contain unbalanced brackets
           inside Perl quotes or quotelike operations. That is,
           "extract_codeblock" is like a combination of "extract_bracketed"
           and "extract_quotelike".

           "extract_codeblock" takes the same initial three parameters as
           "extract_bracketed": a text to process, a set of delimiter brackets
           to look for, and a prefix to match first. It also takes an optional
           fourth parameter, which allows the outermost delimiter brackets to
           be specified separately (see below).

           Omitting the first argument (input text) means process $_ instead.
           Omitting the second argument (delimiter brackets) indicates that
           only '{' is to be used.  Omitting the third argument (prefix
           argument) implies optional whitespace at the start.  Omitting the
           fourth argument (outermost delimiter brackets) indicates that the
           value of the second argument is to be used for the outermost
           delimiters.

           Once the prefix and the outermost opening delimiter bracket have
           been recognized, code blocks are extracted by stepping through the
           input text and trying the following alternatives in sequence:

           1.  Try and match a closing delimiter bracket. If the bracket was
               the same species as the last opening bracket, return the
               substring to that point. If the bracket was mismatched, return
               an error.

           2.  Try to match a quote or quotelike operator. If found, call
               "extract_quotelike" to eat it. If "extract_quotelike" fails,
               return the error it returned. Otherwise go back to step 1.

           3.  Try to match an opening delimiter bracket. If found, call
               "extract_codeblock" recursively to eat the embedded block. If
               the recursive call fails, return an error. Otherwise, go back
               to step 1.

           4.  Unconditionally match a bareword or any other single character,
               and then go back to step 1.

           Examples:

                   # Find a while loop in the text

                           if ($text =~ s/.*?while\s*\{/{/)
                           {
                                   $loop = "while " . extract_codeblock($text);
                           }

                   # Remove the first round-bracketed list (which may include
                   # round- or curly-bracketed code blocks or quotelike operators)

                           extract_codeblock $text, "(){}", '[^(]*';

           The ability to specify a different outermost delimiter bracket is
           useful in some circumstances. For example, in the Parse::RecDescent
           module, parser actions which are to be performed only on a
           successful parse are specified using a "<defer:...>" directive. For
           example:

                   sentence: subject verb object
                                   <defer: {$::theVerb = $item{verb}} >

           Parse::RecDescent uses "extract_codeblock($text, '{}<>')" to
           extract the code within the "<defer:...>" directive, but there's a
           problem.

           A deferred action like this:

                                   <defer: {if ($count>10) {$count--}} >

           will be incorrectly parsed as:

                                   <defer: {if ($count>

           because the "less than" operator is interpreted as a closing
           delimiter.

           But, by extracting the directive using
           "extract_codeblock($text, '{}', undef, '<>')" the '>' character is
           only treated as a delimited at the outermost level of the code
           block, so the directive is parsed correctly.

       "extract_multiple"
           The "extract_multiple" subroutine takes a string to be processed
           and a list of extractors (subroutines or regular expressions) to
           apply to that string.

           In an array context "extract_multiple" returns an array of
           substrings of the original string, as extracted by the specified
           extractors.  In a scalar context, "extract_multiple" returns the
           first substring successfully extracted from the original string. In
           both scalar and void contexts the original string has the first
           successfully extracted substring removed from it. In all contexts
           "extract_multiple" starts at the current "pos" of the string, and
           sets that "pos" appropriately after it matches.

           Hence, the aim of a call to "extract_multiple" in a list context is
           to split the processed string into as many non-overlapping fields
           as possible, by repeatedly applying each of the specified
           extractors to the remainder of the string. Thus "extract_multiple"
           is a generalized form of Perl's "split" subroutine.

           The subroutine takes up to four optional arguments:

           1.  A string to be processed ($_ if the string is omitted or
               "undef")

           2.  A reference to a list of subroutine references and/or qr//
               objects and/or literal strings and/or hash references,
               specifying the extractors to be used to split the string. If
               this argument is omitted (or "undef") the list:

                       [
                               sub { extract_variable($_[0], '') },
                               sub { extract_quotelike($_[0],'') },
                               sub { extract_codeblock($_[0],'{}','') },
                       ]

               is used.

           3.  An number specifying the maximum number of fields to return. If
               this argument is omitted (or "undef"), split continues as long
               as possible.

               If the third argument is N, then extraction continues until N
               fields have been successfully extracted, or until the string
               has been completely processed.

               Note that in scalar and void contexts the value of this
               argument is automatically reset to 1 (under "-w", a warning is
               issued if the argument has to be reset).

           4.  A value indicating whether unmatched substrings (see below)
               within the text should be skipped or returned as fields. If the
               value is true, such substrings are skipped. Otherwise, they are
               returned.

           The extraction process works by applying each extractor in sequence
           to the text string.

           If the extractor is a subroutine it is called in a list context and
           is expected to return a list of a single element, namely the
           extracted text. It may optionally also return two further
           arguments: a string representing the text left after extraction
           (like $' for a pattern match), and a string representing any prefix
           skipped before the extraction (like $` in a pattern match). Note
           that this is designed to facilitate the use of other Text::Balanced
           subroutines with "extract_multiple". Note too that the value
           returned by an extractor subroutine need not bear any relationship
           to the corresponding substring of the original text (see examples
           below).

           If the extractor is a precompiled regular expression or a string,
           it is matched against the text in a scalar context with a leading
           '\G' and the gc modifiers enabled. The extracted value is either $1
           if that variable is defined after the match, or else the complete
           match (i.e. $&).

           If the extractor is a hash reference, it must contain exactly one
           element.  The value of that element is one of the above extractor
           types (subroutine reference, regular expression, or string).  The
           key of that element is the name of a class into which the
           successful return value of the extractor will be blessed.

           If an extractor returns a defined value, that value is immediately
           treated as the next extracted field and pushed onto the list of
           fields.  If the extractor was specified in a hash reference, the
           field is also blessed into the appropriate class,

           If the extractor fails to match (in the case of a regex extractor),
           or returns an empty list or an undefined value (in the case of a
           subroutine extractor), it is assumed to have failed to extract.  If
           none of the extractor subroutines succeeds, then one character is
           extracted from the start of the text and the extraction subroutines
           reapplied. Characters which are thus removed are accumulated and
           eventually become the next field (unless the fourth argument is
           true, in which case they are discarded).

           For example, the following extracts substrings that are valid Perl
           variables:

                   @fields = extract_multiple($text,
                                              [ sub { extract_variable($_[0]) } ],
                                              undef, 1);

           This example separates a text into fields which are quote
           delimited, curly bracketed, and anything else. The delimited and
           bracketed parts are also blessed to identify them (the "anything
           else" is unblessed):

                   @fields = extract_multiple($text,
                              [
                                   { Delim => sub { extract_delimited($_[0],q{'"}) } },
                                   { Brack => sub { extract_bracketed($_[0],'{}') } },
                              ]);

           This call extracts the next single substring that is a valid Perl
           quotelike operator (and removes it from $text):

                   $quotelike = extract_multiple($text,
                                                 [
                                                   sub { extract_quotelike($_[0]) },
                                                 ], undef, 1);

           Finally, here is yet another way to do comma-separated value
           parsing:

                   @fields = extract_multiple($csv_text,
                                             [
                                                   sub { extract_delimited($_[0],q{'"}) },
                                                   qr/([^,]+)(.*)/,
                                             ],
                                             undef,1);

           The list in the second argument means: "Try and extract a ' or "
           delimited string, otherwise extract anything up to a comma...".
           The undef third argument means: "...as many times as possible...",
           and the true value in the fourth argument means "...discarding
           anything else that appears (i.e. the commas)".

           If you wanted the commas preserved as separate fields (i.e. like
           split does if your split pattern has capturing parentheses), you
           would just make the last parameter undefined (or remove it).

       "gen_delimited_pat"
           The "gen_delimited_pat" subroutine takes a single (string) argument
           and
              > builds a Friedl-style optimized regex that matches a string
           delimited by any one of the characters in the single argument. For
           example:

                   gen_delimited_pat(q{'"})

           returns the regex:

                   (?:\"(?:\\\"|(?!\").)*\"|\'(?:\\\'|(?!\').)*\')

           Note that the specified delimiters are automatically quotemeta'd.

           A typical use of "gen_delimited_pat" would be to build special
           purpose tags for "extract_tagged". For example, to properly ignore
           "empty" XML elements (which might contain quoted strings):

                   my $empty_tag = '<(' . gen_delimited_pat(q{'"}) . '|.)+/>';

                   extract_tagged($text, undef, undef, undef, {ignore => [$empty_tag]} );

           "gen_delimited_pat" may also be called with an optional second
           argument, which specifies the "escape" character(s) to be used for
           each delimiter.  For example to match a Pascal-style string (where
           ' is the delimiter and '' is a literal ' within the string):

                   gen_delimited_pat(q{'},q{'});

           Different escape characters can be specified for different
           delimiters.  For example, to specify that '/' is the escape for
           single quotes and '%' is the escape for double quotes:

                   gen_delimited_pat(q{'"},q{/%});

           If more delimiters than escape chars are specified, the last escape
           char is used for the remaining delimiters.  If no escape char is
           specified for a given specified delimiter, '\' is used.

       "delimited_pat"
           Note that "gen_delimited_pat" was previously called
           "delimited_pat".  That name may still be used, but is now
           deprecated.


DIAGNOSTICS

       In a list context, all the functions return "(undef,$original_text)" on
       failure. In a scalar context, failure is indicated by returning "undef"
       (in this case the input text is not modified in any way).

       In addition, on failure in any context, the $@ variable is set.
       Accessing "$@->{error}" returns one of the error diagnostics listed
       below.  Accessing "$@->{pos}" returns the offset into the original
       string at which the error was detected (although not necessarily where
       it occurred!)  Printing $@ directly produces the error message, with
       the offset appended.  On success, the $@ variable is guaranteed to be
       "undef".

       The available diagnostics are:

       "Did not find a suitable bracket: "%s""
           The delimiter provided to "extract_bracketed" was not one of
           '()[]<>{}'.

       "Did not find prefix: /%s/"
           A non-optional prefix was specified but wasn't found at the start
           of the text.

       "Did not find opening bracket after prefix: "%s""
           "extract_bracketed" or "extract_codeblock" was expecting a
           particular kind of bracket at the start of the text, and didn't
           find it.

       "No quotelike operator found after prefix: "%s""
           "extract_quotelike" didn't find one of the quotelike operators "q",
           "qq", "qw", "qx", "s", "tr" or "y" at the start of the substring it
           was extracting.

       "Unmatched closing bracket: "%c""
           "extract_bracketed", "extract_quotelike" or "extract_codeblock"
           encountered a closing bracket where none was expected.

       "Unmatched opening bracket(s): "%s""
           "extract_bracketed", "extract_quotelike" or "extract_codeblock" ran
           out of characters in the text before closing one or more levels of
           nested brackets.

       "Unmatched embedded quote (%s)"
           "extract_bracketed" attempted to match an embedded quoted
           substring, but failed to find a closing quote to match it.

       "Did not find closing delimiter to match '%s'"
           "extract_quotelike" was unable to find a closing delimiter to match
           the one that opened the quote-like operation.

       "Mismatched closing bracket: expected "%c" but found "%s""
           "extract_bracketed", "extract_quotelike" or "extract_codeblock"
           found a valid bracket delimiter, but it was the wrong species. This
           usually indicates a nesting error, but may indicate incorrect
           quoting or escaping.

       "No block delimiter found after quotelike "%s""
           "extract_quotelike" or "extract_codeblock" found one of the
           quotelike operators "q", "qq", "qw", "qx", "s", "tr" or "y" without
           a suitable block after it.

       "Did not find leading dereferencer"
           "extract_variable" was expecting one of '$', '@', or '%' at the
           start of a variable, but didn't find any of them.

       "Bad identifier after dereferencer"
           "extract_variable" found a '$', '@', or '%' indicating a variable,
           but that character was not followed by a legal Perl identifier.

       "Did not find expected opening bracket at %s"
           "extract_codeblock" failed to find any of the outermost opening
           brackets that were specified.

       "Improperly nested codeblock at %s"
           A nested code block was found that started with a delimiter that
           was specified as being only to be used as an outermost bracket.

       "Missing second block for quotelike "%s""
           "extract_codeblock" or "extract_quotelike" found one of the
           quotelike operators "s", "tr" or "y" followed by only one block.

       "No match found for opening bracket"
           "extract_codeblock" failed to find a closing bracket to match the
           outermost opening bracket.

       "Did not find opening tag: /%s/"
           "extract_tagged" did not find a suitable opening tag (after any
           specified prefix was removed).

       "Unable to construct closing tag to match: /%s/"
           "extract_tagged" matched the specified opening tag and tried to
           modify the matched text to produce a matching closing tag (because
           none was specified). It failed to generate the closing tag, almost
           certainly because the opening tag did not start with a bracket of
           some kind.

       "Found invalid nested tag: %s"
           "extract_tagged" found a nested tag that appeared in the "reject"
           list (and the failure mode was not "MAX" or "PARA").

       "Found unbalanced nested tag: %s"
           "extract_tagged" found a nested opening tag that was not matched by
           a corresponding nested closing tag (and the failure mode was not
           "MAX" or "PARA").

       "Did not find closing tag"
           "extract_tagged" reached the end of the text without finding a
           closing tag to match the original opening tag (and the failure mode
           was not "MAX" or "PARA").


EXPORTS

       The following symbols are, or can be, exported by this module:

       Default Exports
           None.

       Optional Exports
           "extract_delimited", "extract_bracketed", "extract_quotelike",
           "extract_codeblock", "extract_variable", "extract_tagged",
           "extract_multiple", "gen_delimited_pat", "gen_extract_tagged",
           "delimited_pat".

       Export Tags
           ":ALL"
               "extract_delimited", "extract_bracketed", "extract_quotelike",
               "extract_codeblock", "extract_variable", "extract_tagged",
               "extract_multiple", "gen_delimited_pat", "gen_extract_tagged",
               "delimited_pat".


KNOWN BUGS

       See
       <https://rt.cpan.org/Dist/Display.html?Status=Active&Queue=Text-Balanced>.


FEEDBACK

       Patches, bug reports, suggestions or any other feedback is welcome.

       Patches can be sent as GitHub pull requests at
       <https://github.com/steve-m-hay/Text-Balanced/pulls>.

       Bug reports and suggestions can be made on the CPAN Request Tracker at
       <https://rt.cpan.org/Public/Bug/Report.html?Queue=Text-Balanced>.

       Currently active requests on the CPAN Request Tracker can be viewed at
       <https://rt.cpan.org/Public/Dist/Display.html?Status=Active;Queue=Text-Balanced>.

       Please test this distribution.  See CPAN Testers Reports at
       <https://www.cpantesters.org/> for details of how to get involved.

       Previous test results on CPAN Testers Reports can be viewed at
       <https://www.cpantesters.org/distro/T/Text-Balanced.html>.

       Please rate this distribution on CPAN Ratings at
       <https://cpanratings.perl.org/rate/?distribution=Text-Balanced>.


AVAILABILITY

       The latest version of this module is available from CPAN (see "CPAN" in
       perlmodlib for details) at

       <https://metacpan.org/release/Text-Balanced> or

       <https://www.cpan.org/authors/id/S/SH/SHAY/> or

       <https://www.cpan.org/modules/by-module/Text/>.

       The latest source code is available from GitHub at
       <https://github.com/steve-m-hay/Text-Balanced>.


INSTALLATION

       See the INSTALL file.


AUTHOR

       Damian Conway <damian@conway.org <mailto:damian@conway.org>>.

       Steve Hay <shay@cpan.org <mailto:shay@cpan.org>> is now maintaining
       Text::Balanced as of version 2.03.


COPYRIGHT

       Copyright (C) 1997-2001 Damian Conway.  All rights reserved.

       Copyright (C) 2009 Adam Kennedy.

       Copyright (C) 2015, 2020 Steve Hay.  All rights reserved.


LICENCE

       This module is free software; you can redistribute it and/or modify it
       under the same terms as Perl itself, i.e. under the terms of either the
       GNU General Public License or the Artistic License, as specified in the
       LICENCE file.


VERSION

       Version 2.04


DATE

       11 Dec 2020


HISTORY

       See the Changes file.



perl v5.34.0                      2021-01-20               Text::Balanced(3pm)

perl 5.34.0 - Generated Fri Mar 4 14:49:15 CST 2022
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