## SYNOPSIS

           flex  [-bcdfhilnpstvwBFILTV78+? -C[aefFmr] -ooutput -Ppre
           fix -Sskeleton] [--help --version] [filename ...]

## OVERVIEW

           This manual describes flex, a tool for generating programs
           that   perform   pattern-matching  on  text.   The  manual
           includes both tutorial and reference sections:

               Description
                   a brief overview of the tool

               Some Simple Examples

               Format Of The Input File

               Patterns
                   the extended regular expressions used by flex

               How The Input Is Matched
                   the rules for determining what has been matched

               Actions
                   how to specify what to do when a pattern is matched

               The Generated Scanner
                   details regarding the scanner that flex produces;
                   how to control the input source

               Start Conditions
                   introducing context into your scanners, and
                   managing "mini-scanners"

               Multiple Input Buffers
                   how to manipulate multiple input sources; how to
                   scan from strings instead of files

               End-of-file Rules
                   special rules for matching the end of the input

               Miscellaneous Macros
                   a summary of macros available to the actions

               Values Available To The User
                   a summary of values available to the actions

               Interfacing With Yacc
                   connecting flex scanners together with yacc parsers

               Options
                   flex command-line options, and the "%option"
                   directive
                   it generates) whose meanings might not be apparent

               Files
                   files used by flex

               Deficiencies / Bugs
                   known problems with flex

               See Also
                   other documentation, related tools

               Author
                   includes contact information

## DESCRIPTION

           flex is a tool for  generating  scanners:  programs  which
           recognized lexical patterns in text.  flex reads the given
           input files, or its standard input if no  file  names  are
           given,  for  a  description of a scanner to generate.  The
           description is in the form of pairs of regular expressions
           and  C  code,  called  rules. flex generates as output a C
           source file, lex.yy.c, which defines  a  routine  yylex().
           This  file is compiled and linked with the -lfl library to
           produce an executable.  When the  executable  is  run,  it
           analyzes  its input for occurrences of the regular expres
           sions.  Whenever it finds one, it executes the correspond
           ing C code.

## SOME SIMPLE EXAMPLES

           First  some  simple  examples to get the flavor of how one
           uses flex.  The following flex input specifies  a  scanner
           which  whenever  it  encounters the string "username" will
           replace it with the user's login name:

               %%
               username    printf( "%s", getlogin() );

           By default, any text not matched  by  a  flex  scanner  is
           copied to the output, so the net effect of this scanner is
           to copy its input file to its output with each  occurrence
           of  "username" expanded.  In this input, there is just one
           rule.  "username" is the pattern and the "printf"  is  the
           action.  The "%%" marks the beginning of the rules.

           Here's another simple example:

                       int num_lines = 0, num_chars = 0;

               %%
               \n      ++num_lines; ++num_chars;
               .       ++num_chars;

           tine declared after the second "%%".  There are two rules,
           one which matches a newline ("\n") and increments both the
           line count and the character count, and one which  matches
           any  character  other than a newline (indicated by the "."
           regular expression).

           A somewhat more complicated example:

               /* scanner for a toy Pascal-like language */

               %{
               /* need this for the call to atof() below */
               #include <math.h>
               %}

               DIGIT    [0-9]
               ID       [a-z][a-z0-9]*

               %%

               {DIGIT}+    {
                           printf( "An integer: %s (%d)\n", yytext,
                                   atoi( yytext ) );
                           }

               {DIGIT}+"."{DIGIT}*        {
                           printf( "A float: %s (%g)\n", yytext,
                                   atof( yytext ) );
                           }

               if|then|begin|end|procedure|function        {
                           printf( "A keyword: %s\n", yytext );
                           }

               {ID}        printf( "An identifier: %s\n", yytext );

               "+"|"-"|"*"|"/"   printf( "An operator: %s\n", yytext );

               "{"[^}\n]*"}"     /* eat up one-line comments */

               [ \t\n]+          /* eat up whitespace */

               .           printf( "Unrecognized character: %s\n", yytext );

               %%

               main( argc, argv )
               int argc;
               char **argv;
                   {
                   ++argv, --argc;  /* skip over program name */
                   if ( argc > 0 )

## FORMAT OF THE INPUT FILE

           The  flex input file consists of three sections, separated
           by a line with just %% in it:

               definitions
               %%
               rules
               %%
               user code

           The definitions section contains  declarations  of  simple
           name  definitions  to  simplify the scanner specification,
           and declarations of start conditions, which are  explained
           in a later section.

           Name definitions have the form:

               name definition

           The  "name" is a word beginning with a letter or an under
           score ('_') followed by zero or more letters, digits, '_',
           or  '-'  (dash).   The definition is taken to begin at the
           first non-white-space character  following  the  name  and
           continuing  to  the  end  of the line.  The definition can
           subsequently be referred to  using  "{name}",  which  will
           expand to "(definition)".  For example,

               DIGIT    [0-9]
               ID       [a-z][a-z0-9]*

           defines "DIGIT" to be a regular expression which matches a
           single digit, and "ID" to be a  regular  expression  which
           matches  a letter followed by zero-or-more letters-or-dig
           its.  A subsequent reference to

               {DIGIT}+"."{DIGIT}*

           is identical to

               ([0-9])+"."([0-9])*

           and matches one-or-more digits followed by a '.'  followed
           by zero-or-more digits.

           The  rules  section of the flex input contains a series of
           rules of the form:

               pattern   action

           where the pattern must be unindented and the  action  must
           begin on the same line.

           In  the  rules section, any indented or %{} text appearing
           before the first rule may be  used  to  declare  variables
           which  are  local  to  the scanning routine and (after the
           declarations) code which is to be  executed  whenever  the
           scanning  routine  is entered.  Other indented or %{} text
           in the rule section is still copied to the output, but its
           meaning is not well-defined and it may well cause compile-
           time errors (this feature is present for POSIX compliance;
           see below for other such features).

           In the definitions section (but not in the rules section),
           an unindented comment (i.e., a line beginning  with  "/*")
           is also copied verbatim to the output up to the next "*/".

## PATTERNS

           The patterns in the input are written  using  an  extended
           set of regular expressions.  These are:

               x          match the character 'x'
               .          any character (byte) except newline
               [xyz]      a "character class"; in this case, the pattern
                            matches either an 'x', a 'y', or a 'z'
               [abj-oZ]   a "character class" with a range in it; matches
                            an 'a', a 'b', any letter from 'j' through 'o',
                            or a 'Z'
               [^A-Z]     a "negated character class", i.e., any character
                            but those in the class.  In this case, any
                            character EXCEPT an uppercase letter.
               [^A-Z\n]   any character EXCEPT an uppercase letter or
                            a newline
               r*         zero or more r's, where r is any regular expression
               r+         one or more r's
               r?         zero or one r's (that is, "an optional r")
               r{2,5}     anywhere from two to five r's
               r{2,}      two or more r's
               r{4}       exactly 4 r's
               {name}     the expansion of the "name" definition
                          (see above)
               "[xyz]\"foo"
                          the literal string: [xyz]"foo
               \X         if X is an 'a', 'b', 'f', 'n', 'r', 't', or 'v',
                            then the ANSI-C interpretation of \x.
                            Otherwise, a literal 'X' (used to escape
                            operators such as '*')
               \0         a NUL character (ASCII code 0)
               \123       the character with octal value 123
               \x2a       the character with hexadecimal value 2a
               (r)        match an r; parentheses are used to override
                            precedence (see below)

               rs         the regular expression r followed by the
                            cannot match correctly; see notes in the
                            Deficiencies / Bugs section below regarding
                            "dangerous trailing context".)
               ^r         an r, but only at the beginning of a line (i.e.,
                            which just starting to scan, or right after a
                            newline has been scanned).
               r$         an r, but only at the end of a line (i.e., just
                            before a newline).  Equivalent to "r/\n".

                          Note that flex's notion of "newline" is exactly
                          whatever the C compiler used to compile flex
                          interprets '\n' as; in particular, on some DOS
                          systems you must either filter out \r's in the
                          input yourself, or explicitly use r/\r\n for "r$".

               <s>r       an r, but only in start condition s (see
                            below for discussion of start conditions)
               <s1,s2,s3>r
                          same, but in any of start conditions s1,
                            s2, or s3
               <*>r       an r in any start condition, even an exclusive one.

               <<EOF>>    an end-of-file
               <s1,s2><<EOF>>
                          an end-of-file when in start condition s1 or s2

           Note that inside of a character class, all regular expres
           sion operators lose their special  meaning  except  escape
           ('\') and the character class operators, '-', ']', and, at
           the beginning of the class, '^'.

           The regular expressions listed above are grouped according
           to  precedence, from highest precedence at the top to low
           est at the bottom.   Those  grouped  together  have  equal
           precedence.  For example,

               foo|bar*

           is the same as

               (foo)|(ba(r*))

           since the '*' operator has higher precedence than concate
           nation, and concatenation higher than  alternation  ('|').
           This  pattern therefore matches either the string "foo" or
           the string "ba" followed by zero-or-more  r's.   To  match
           "foo" or zero-or-more "bar"'s, use:

               foo|(bar)*

               [:cntrl:] [:digit:] [:graph:]
               [:lower:] [:print:] [:punct:]
               [:space:] [:upper:] [:xdigit:]

           These expressions all designate a set of characters equiv
           alent to the corresponding standard C isXXX function.  For
           example,  [:alnum:]  designates those characters for which
           isalnum() returns true - i.e., any alphabetic or  numeric.
           Some  systems  don't  provide  isblank(),  so flex defines
           [:blank:] as a blank or a tab.

           For example,  the  following  character  classes  are  all
           equivalent:

               [[:alnum:]]
               [[:alpha:][:digit:]
               [[:alpha:]0-9]
               [a-zA-Z0-9]

           If  your  scanner  is case-insensitive (the -i flag), then
           [:upper:] and [:lower:] are equivalent to [:alpha:].

           Some notes on patterns:

           -      A negated character class such as the example "[^A-
                  Z]"  above  will match a newline unless "\n" (or an
                  equivalent escape sequence) is one of  the  charac
                  ters  explicitly  present  in the negated character
                  class (e.g., "[^A-Z\n]").  This is unlike how  many
                  other  regular expression tools treat negated char
                  acter classes, but unfortunately the  inconsistency
                  is   historically  entrenched.   Matching  newlines
                  means that a  pattern  like  [^"]*  can  match  the
                  entire  input  unless  there's another quote in the
                  input.

           -      A rule can have at most one  instance  of  trailing
                  context  (the  '/'  operator  or the '$' operator).
                  The start condition, '^',  and  "<<EOF>>"  patterns
                  can  only occur at the beginning of a pattern, and,
                  as well as with '/'  and  '$',  cannot  be  grouped
                  inside  parentheses.  A '^' which does not occur at
                  the beginning of a rule or a  '$'  which  does  not
                  occur  at the end of a rule loses its special prop
                  erties and is treated as a normal character.

                  The following are illegal:

                      foo/bar$
                      <sc1>foo<sc2>bar

                  Note that  the  first  of  these,  can  be  written

                  A similar trick will work for matching a foo  or  a
                  bar-at-the-beginning-of-a-line.

## HOW THE INPUT IS MATCHED

           When  the  generated scanner is run, it analyzes its input
           looking for strings which match any of its  patterns.   If
           it  finds  more  than one match, it takes the one matching
           the most text (for trailing context rules,  this  includes
           the  length of the trailing part, even though it will then
           be returned to the  input).   If  it  finds  two  or  more
           matches  of  the same length, the rule listed first in the
           flex input file is chosen.

           Once the match is determined, the  text  corresponding  to
           the  match  (called  the  token)  is made available in the
           global character pointer yytext, and  its  length  in  the
           global  integer  yyleng.   The action corresponding to the
           matched pattern is then executed (a more detailed descrip
           tion  of actions follows), and then the remaining input is
           scanned for another match.

           If no match is found, then the default rule  is  executed:
           the  next character in the input is considered matched and
           copied to the standard output.  Thus, the  simplest  legal
           flex input is:

               %%

           which  generates  a  scanner  that simply copies its input
           (one character at a time) to its output.

           Note that yytext can be defined  in  two  different  ways:
           either  as  a  character  pointer or as a character array.
           You can control which definition flex  uses  by  including
           one  of  the  special directives %pointer or %array in the
           first (definitions)  section  of  your  flex  input.   The
           default is %pointer, unless you use the -l lex compatibil
           ity option, in which case yytext will be  an  array.   The
           advantage  of using %pointer is substantially faster scan
           ning and no  buffer  overflow  when  matching  very  large
           tokens (unless you run out of dynamic memory).  The disad
           vantage is that you are restricted in how your actions can
           modify  yytext  (see  the  next section), and calls to the
           unput() function destroys the present contents of  yytext,
           which  can  be a considerable porting headache when moving
           between different lex versions.

           The advantage of %array is that you can then modify yytext
           to  your  heart's  content,  and  calls  to unput() do not
           destroy yytext (see  below).   Furthermore,  existing  lex
           programs sometimes access yytext externally using declara
           token from the beginning,  so  matching  such  tokens  can
           prove slow.  yytext presently does not dynamically grow if
           a call to unput() results in too much  text  being  pushed
           back; instead, a run-time error results.

           Also  note  that  you  cannot  use %array with C++ scanner
           classes (the c++ option; see below).

## ACTIONS

           Each pattern in a rule has a corresponding  action,  which
           can be any arbitrary C statement.  The pattern ends at the
           first non-escaped whitespace character; the  remainder  of
           the line is its action.  If the action is empty, then when
           the pattern is matched the  input  token  is  simply  dis
           carded.  For example, here is the specification for a pro
           gram which deletes all occurrences of "zap  me"  from  its
           input:

               %%
               "zap me"

           (It  will  copy  all  other characters in the input to the
           output since they will be matched by the default rule.)

           Here is a program which  compresses  multiple  blanks  and
           tabs  down  to  a single blank, and throws away whitespace
           found at the end of a line:

               %%
               [ \t]+        putchar( ' ' );
               [ \t]+$       /* ignore this token */

           If the action contains a '{', then the action  spans  till
           the  balancing '}' is found, and the action may cross mul
           tiple lines.  flex knows about C strings and comments  and
           won't  be  fooled  by  braces  found within them, but also
           allows actions to begin with  %{  and  will  consider  the
           action to be all the text up to the next %} (regardless of
           ordinary braces inside the action).

           An action consisting solely of a vertical bar ('|')  means
           "same  as the action for the next rule."  See below for an
           illustration.

           Actions can include arbitrary  C  code,  including  return
           statements  to  return  a value to whatever routine called
           yylex().  Each time yylex() is called  it  continues  pro
           cessing tokens from where it last left off until it either
           reaches the end of the file or executes a return.

           Actions are free to modify yytext except  for  lengthening
           -      BEGIN  followed  by  the  name of a start condition
                  places the scanner in the corresponding start  con
                  dition (see below).

           -      REJECT  directs  the  scanner  to proceed on to the
                  "second best" rule which matched the  input  (or  a
                  prefix  of  the  input).   The  rule  is  chosen as
                  described above in "How the Input is Matched",  and
                  yytext  and  yyleng  set  up appropriately.  It may
                  either be one which matched as  much  text  as  the
                  originally  chosen  rule but came later in the flex
                  input file, or one which matched  less  text.   For
                  example, the following will both count the words in
                  the input and call the routine  special()  whenever
                  "frob" is seen:

                              int word_count = 0;
                      %%

                      frob        special(); REJECT;
                      [^ \t\n]+   ++word_count;

                  Without the REJECT, any "frob"'s in the input would
                  not be counted as words, since the scanner normally
                  executes  only  one  action  per  token.   Multiple
                  REJECT's are allowed, each  one  finding  the  next
                  best  choice  to  the  currently  active rule.  For
                  example, when the following scanner scans the token
                  "abcd", it will write "abcdabcaba" to the output:

                      %%
                      a        |
                      ab       |
                      abc      |
                      abcd     ECHO; REJECT;
                      .|\n     /* eat up any unmatched character */

                  (The  first  three  rules share the fourth's action
                  since they use the special '|' action.)  REJECT  is
                  a  particularly expensive feature in terms of scan
                  ner performance; if it is used in any of the  scan
                  ner's  actions  it  will slow down all of the scan
                  ner's matching.  Furthermore, REJECT cannot be used
                  with the -Cf or -CF options (see below).

                  Note  also  that  unlike the other special actions,
                  REJECT is a branch; code immediately  following  it
                  in the action will not be executed.

           -      yymore()  tells  the  scanner that the next time it
                  matches a rule, the corresponding token  should  be
                  appended  onto  the  current value of yytext rather

           Two notes regarding  use  of  yymore().   First,  yymore()
           depends  on  the  value of yyleng correctly reflecting the
           size of the current token, so you must not  modify  yyleng
           if  you  are  using  yymore().   Second,  the  presence of
           yymore() in the scanner's action entails a  minor  perfor
           mance penalty in the scanner's matching speed.

           -      yyless(n) returns all but the first n characters of
                  the current token back to the input  stream,  where
                  they  will  be rescanned when the scanner looks for
                  the next match.  yytext  and  yyleng  are  adjusted
                  appropriately  (e.g., yyleng will now be equal to n
                  ).  For example, on the input "foobar" the  follow
                  ing will write out "foobarbar":

                      %%
                      foobar    ECHO; yyless(3);
                      [a-z]+    ECHO;

                  An  argument  of  0 to yyless will cause the entire
                  current input string to be scanned  again.   Unless
                  you've  changed  how  the scanner will subsequently
                  process its input (using BEGIN, for example),  this
                  will result in an endless loop.

           Note  that  yyless  is a macro and can only be used in the
           flex input file, not from other source files.

           -      unput(c) puts the character c back onto  the  input
                  stream.   It  will  be  the next character scanned.
                  The following action will take  the  current  token
                  and  cause it to be rescanned enclosed in parenthe
                  ses.

                      {
                      int i;
                      /* Copy yytext because unput() trashes yytext */
                      char *yycopy = strdup( yytext );
                      unput( ')' );
                      for ( i = yyleng - 1; i >= 0; --i )
                          unput( yycopy[i] );
                      unput( '(' );
                      free( yycopy );
                      }

                  Note that since each unput() puts the given charac
                  ter  back  at  the  beginning  of the input stream,
                  pushing back strings must be done back-to-front.

           An important potential problem when using unput() is  that
           if you are using %pointer (the default), a call to unput()
           destroys the contents of yytext, starting with its  right
                      "/*"        {
                                  register int c;

                                  for ( ; ; )
                                      {
                                      while ( (c = input()) != '*' &&
                                              c != EOF )
                                          ;    /* eat up text of comment */

                                      if ( c == '*' )
                                          {
                                          while ( (c = input()) == '*' )
                                              ;
                                          if ( c == '/' )
                                              break;    /* found the end */
                                          }

                                      if ( c == EOF )
                                          {
                                          error( "EOF in comment" );
                                          break;
                                          }
                                      }
                                  }

                  (Note that if the scanner is  compiled  using  C++,
                  then  input()  is instead referred to as yyinput(),
                  in order to avoid a name clash with the C++  stream
                  by the name of input.)

           -      YY_FLUSH_BUFFER   flushes  the  scanner's  internal
                  buffer so that the next time the  scanner  attempts
                  to  match  a token, it will first refill the buffer
                  using YY_INPUT (see The Generated Scanner,  below).
                  This  action  is a special case of the more general
                  yy_flush_buffer() function, described below in  the
                  section Multiple Input Buffers.

           -      yyterminate()  can  be  used  in  lieu  of a return
                  statement in an action.  It terminates the  scanner
                  and returns a 0 to the scanner's caller, indicating
                  "all done".   By  default,  yyterminate()  is  also
                  called when an end-of-file is encountered.  It is a
                  macro and may be redefined.

## THE GENERATED SCANNER

           The output of flex is the file  lex.yy.c,  which  contains
           the  scanning  routine yylex(), a number of tables used by
           it for matching tokens, and a number of auxiliary routines
           and macros.  By default, yylex() is declared as follows:

               int yylex()

           style/non-prototyped function declaration, you must termi
           nate the definition with a semi-colon (;).

           Whenever yylex() is  called,  it  scans  tokens  from  the
           global input file yyin (which defaults to stdin).  It con
           tinues until it either reaches an  end-of-file  (at  which
           point  it  returns the value 0) or one of its actions exe
           cutes a return statement.

           If the scanner reaches an  end-of-file,  subsequent  calls
           are undefined unless either yyin is pointed at a new input
           file (in which case scanning continues from that file), or
           yyrestart()  is called.  yyrestart() takes one argument, a
           FILE * pointer  (which  can  be  nil,  if  you've  set  up
           YY_INPUT  to scan from a source other than yyin), and ini
           tializes yyin for scanning from  that  file.   Essentially
           there  is  no  difference between just assigning yyin to a
           new input file or using yyrestart() to do so;  the  latter
           is  available  for compatibility with previous versions of
           flex, and because it can be used to switch input files  in
           the middle of scanning.  It can also be used to throw away
           the current input buffer, by calling it with  an  argument
           of yyin; but better is to use YY_FLUSH_BUFFER (see above).
           Note that yyrestart() does not reset the  start  condition
           to INITIAL (see Start Conditions, below).

           If yylex() stops scanning due to executing a return state
           ment in one of the actions, the scanner may then be called
           again and it will resume scanning where it left off.

           By  default  (and for purposes of efficiency), the scanner
           uses block-reads rather than simple getc() calls  to  read
           characters from yyin.  The nature of how it gets its input
           can  be  controlled  by  defining  the   YY_INPUT   macro.
           YY_INPUT's           calling          sequence          is
           "YY_INPUT(buf,result,max_size)".  Its action is  to  place
           up  to  max_size characters in the character array buf and
           return in the integer variable result either the number of
           characters  read  or  the constant YY_NULL (0 on Unix sys
           tems) to indicate EOF.  The default  YY_INPUT  reads  from
           the global file-pointer "yyin".

           A  sample  definition of YY_INPUT (in the definitions sec
           tion of the input file):

               %{
               #define YY_INPUT(buf,result,max_size) \
                   { \
                   int c = getchar(); \
                   result = (c == EOF) ? YY_NULL : (buf[0] = c, 1); \
                   }
               %}

           you  must  either  use %option noyywrap (in which case the
           scanner behaves as though yywrap()  returned  1),  or  you
           must  link  with -lfl to obtain the default version of the
           routine, which always returns 1.

           Three routines are available for scanning  from  in-memory
           buffers     rather     than    files:    yy_scan_string(),
           yy_scan_bytes(), and yy_scan_buffer().  See the discussion
           of them below in the section Multiple Input Buffers.

           The  scanner  writes  its  ECHO output to the yyout global
           (default, stdout), which may be redefined by the user sim
           ply by assigning it to some other FILE pointer.

## START CONDITIONS

           flex  provides  a  mechanism  for conditionally activating
           rules.  Any rule whose pattern  is  prefixed  with  "<sc>"
           will  only be active when the scanner is in the start con
           dition named "sc".  For example,

               <STRING>[^"]*        { /* eat up the string body ... */
                           ...
                           }

           will be active only when the scanner is  in  the  "STRING"
           start condition, and

               <INITIAL,STRING,QUOTE>\.        { /* handle an escape ... */
                           ...
                           }

           will  be  active  only when the current start condition is
           either "INITIAL", "STRING", or "QUOTE".

           Start conditions are declared in the  definitions  (first)
           section of the input using unindented lines beginning with
           either %s or %x followed by a list of names.   The  former
           declares  inclusive start conditions, the latter exclusive
           start conditions.  A start condition  is  activated  using
           the  BEGIN  action.   Until  the next BEGIN action is exe
           cuted, rules with the given start condition will be active
           and  rules  with  other start conditions will be inactive.
           If the start condition is inclusive, then  rules  with  no
           start  conditions  at  all  will also be active.  If it is
           exclusive, then only rules qualified with the start condi
           tion  will  be  active.   A set of rules contingent on the
           same exclusive start condition describe a scanner which is
           independent  of  any of the other rules in the flex input.
           Because of this, exclusive start conditions make  it  easy
           to  specify  "mini-scanners"  which  scan  portions of the
           input that  are  syntactically  different  from  the  rest
           (e.g., comments).

               %x example
               %%

               <example>foo   do_something();

               <INITIAL,example>bar    something_else();

           Without the <INITIAL,example> qualifier, the  bar  pattern
           in  the  second example wouldn't be active (i.e., couldn't
           match) when in start condition example.  If we  just  used
           <example>  to  qualify  bar, though, then it would only be
           active in example and not in INITIAL, while in  the  first
           example  it's active in both, because in the first example
           the example startion condition is an inclusive (%s)  start
           condition.

           Also  note  that the special start-condition specifier <*>
           matches every start condition.  Thus,  the  above  example
           could also have been written;

               %x example
               %%

               <example>foo   do_something();

               <*>bar    something_else();

           The default rule (to ECHO any unmatched character) remains
           active in start conditions.  It is equivalent to:

               <*>.|\n     ECHO;

           BEGIN(0) returns to the  original  state  where  only  the
           rules with no start conditions are active.  This state can
           also be referred to as the start-condition  "INITIAL",  so
           BEGIN(INITIAL)  is equivalent to BEGIN(0).  (The parenthe
           ses around the start condition name are not  required  but
           are considered good style.)

           BEGIN  actions  can  also be given as indented code at the
           beginning of the rules section.  For example, the  follow
           ing  will  cause  the scanner to enter the "SPECIAL" start
           condition whenever yylex() is called and the global  vari
           able enter_special is true:

                       int enter_special;

               %x SPECIAL
               %%

               %{
               #include <math.h>
               %}
               %s expect

               %%
               expect-floats        BEGIN(expect);

               <expect>[0-9]+"."[0-9]+      {
                           printf( "found a float, = %f\n",
                                   atof( yytext ) );
                           }
               <expect>\n           {
                           /* that's the end of the line, so
                            * we need another "expect-number"
                            * before we'll recognize any more
                            * numbers
                            */
                           BEGIN(INITIAL);
                           }

               [0-9]+      {
                           printf( "found an integer, = %d\n",
                                   atoi( yytext ) );
                           }

               "."         printf( "found a dot\n" );

           Here  is  a scanner which recognizes (and discards) C com
           ments while maintaining a count of the current input line.

               %x comment
               %%
                       int line_num = 1;

               "/*"         BEGIN(comment);

               <comment>[^*\n]*        /* eat anything that's not a '*' */
               <comment>"*"+[^*/\n]*   /* eat up '*'s not followed by '/'s */
               <comment>\n             ++line_num;
               <comment>"*"+"/"        BEGIN(INITIAL);

           This  scanner  goes  to  a bit of trouble to match as much
           text  as  possible  with  each  rule.   In  general,  when
           attempting  to  write a high-speed scanner try to match as
           much possible in each rule, as it's a big win.

           Note that start-conditions names are really integer values
           and  can  be  stored  as  such.   Thus, the above could be
           extended in the following fashion:

                            BEGIN(comment);
                            }

               <comment>[^*\n]*        /* eat anything that's not a '*' */
               <comment>"*"+[^*/\n]*   /* eat up '*'s not followed by '/'s */
               <comment>\n             ++line_num;
               <comment>"*"+"/"        BEGIN(comment_caller);

           Furthermore, you can access the  current  start  condition
           using the integer-valued YY_START macro.  For example, the
           above assignments to comment_caller could instead be writ
           ten

               comment_caller = YY_START;

           Flex provides YYSTATE as an alias for YY_START (since that
           is what's used by AT&T lex).

           Note that start conditions do not  have  their  own  name-
           space;  %s's and %x's declare names in the same fashion as
           #define's.

           Finally, here's an example of how to match C-style  quoted
           strings   using   exclusive  start  conditions,  including
           expanded escape sequences (but not including checking  for
           a string that's too long):

               %x str

               %%
                       char string_buf[MAX_STR_CONST];
                       char *string_buf_ptr;

               \"      string_buf_ptr = string_buf; BEGIN(str);

               <str>\"        { /* saw closing quote - all done */
                       BEGIN(INITIAL);
                       *string_buf_ptr = '\0';
                       /* return string constant token type and
                        * value to parser
                        */
                       }

               <str>\n        {
                       /* error - unterminated string constant */
                       /* generate error message */
                       }

               <str>\\[0-7]{1,3} {
                       /* octal escape sequence */
                       int result;

               <str>\\n  *string_buf_ptr++ = '\n';
               <str>\\t  *string_buf_ptr++ = '\t';
               <str>\\r  *string_buf_ptr++ = '\r';
               <str>\\b  *string_buf_ptr++ = '\b';
               <str>\\f  *string_buf_ptr++ = '\f';

               <str>\\(.|\n)  *string_buf_ptr++ = yytext[1];

               <str>[^\\\n\"]+        {
                       char *yptr = yytext;

                       while ( *yptr )
                               *string_buf_ptr++ = *yptr++;
                       }

           Often,  such as in some of the examples above, you wind up
           writing a whole bunch of rules all preceded  by  the  same
           start  condition(s).   Flex makes this a little easier and
           cleaner by introducing a notion of start condition  scope.
           A start condition scope is begun with:

               <SCs>{

           where  SCs  is  a  list  of  one or more start conditions.
           Inside the start condition scope, every rule automatically
           has  the  prefix  <SCs>  applied  to it, until a '}' which
           matches the initial '{'.  So, for example,

               <ESC>{
                   "\\n"   return '\n';
                   "\\r"   return '\r';
                   "\\f"   return '\f';
                   "\\0"   return '\0';
               }

           is equivalent to:

               <ESC>"\\n"  return '\n';
               <ESC>"\\r"  return '\r';
               <ESC>"\\f"  return '\f';
               <ESC>"\\0"  return '\0';

           Start condition scopes may be nested.

           Three routines are available for  manipulating  stacks  of
           start conditions:

           void yy_push_state(int new_state)
                  pushes  the current start condition onto the top of
                  the start condition stack and switches to new_state

           To use start condition stacks, your scanner must include a
           %option stack directive (see Options below).

## MULTIPLE INPUT BUFFERS

           Some  scanners  (such  as  those  which  support "include"
           files) require reading from  several  input  streams.   As
           flex  scanners  do a large amount of buffering, one cannot
           control where the next input will be read from  by  simply
           writing a YY_INPUT which is sensitive to the scanning con
           text.  YY_INPUT is only called when  the  scanner  reaches
           the  end  of  its  buffer,  which may be a long time after
           scanning a statement such as an "include"  which  requires
           switching the input source.

           To  negotiate  these  sorts  of  problems, flex provides a
           mechanism for  creating  and  switching  between  multiple
           input buffers.  An input buffer is created by using:

               YY_BUFFER_STATE yy_create_buffer( FILE *file, int size )

           which takes a FILE pointer and a size and creates a buffer
           associated with the given file and large  enough  to  hold
           size  characters  (when  in doubt, use YY_BUF_SIZE for the
           size).  It returns a  YY_BUFFER_STATE  handle,  which  may
           then  be  passed  to  other  routines  (see  below).   The
           YY_BUFFER_STATE type is a  pointer  to  an  opaque  struct
           yy_buffer_state  structure,  so  you may safely initialize
           YY_BUFFER_STATE variables to ((YY_BUFFER_STATE) 0) if  you
           wish,  and  also refer to the opaque structure in order to
           correctly declare input buffers in source files other than
           that  of  your scanner.  Note that the FILE pointer in the
           call to yy_create_buffer is only used as the value of yyin
           seen by YY_INPUT; if you redefine YY_INPUT so it no longer
           uses yyin, then you can safely pass a nil FILE pointer  to
           yy_create_buffer.   You select a particular buffer to scan
           from using:

               void yy_switch_to_buffer( YY_BUFFER_STATE new_buffer )

           switches the scanner's input buffer so  subsequent  tokens
           will      come     from     new_buffer.      Note     that
           yy_switch_to_buffer() may  be  used  by  yywrap()  to  set
           things up for continued scanning, instead of opening a new
           file and pointing yyin at it.  Note  also  that  switching
           input sources via either yy_switch_to_buffer() or yywrap()
           does not change the start condition.

               void yy_delete_buffer( YY_BUFFER_STATE buffer )

           is used to reclaim the storage associated with  a  buffer.
           (  buffer can be nil, in which case the routine does noth
           YY_BUFFER_STATE handle to the current buffer.

           Here  is  an example of using these features for writing a
           scanner which expands include files (the  <<EOF>>  feature
           is discussed below):

               /* the "incl" state is used for picking up the name
                * of an include file
                */
               %x incl

               %{
               #define MAX_INCLUDE_DEPTH 10
               YY_BUFFER_STATE include_stack[MAX_INCLUDE_DEPTH];
               int include_stack_ptr = 0;
               %}

               %%
               include             BEGIN(incl);

               [a-z]+              ECHO;
               [^a-z\n]*\n?        ECHO;

               <incl>[ \t]*      /* eat the whitespace */
               <incl>[^ \t\n]+   { /* got the include file name */
                       if ( include_stack_ptr >= MAX_INCLUDE_DEPTH )
                           {
                           fprintf( stderr, "Includes nested too deeply" );
                           exit( 1 );
                           }

                       include_stack[include_stack_ptr++] =
                           YY_CURRENT_BUFFER;

                       yyin = fopen( yytext, "r" );

                       if ( ! yyin )
                           error( ... );

                       yy_switch_to_buffer(
                           yy_create_buffer( yyin, YY_BUF_SIZE ) );

                       BEGIN(INITIAL);
                       }

               <<EOF>> {
                       if ( --include_stack_ptr < 0 )
                           {
                           yyterminate();
                           }

                       else

           start scanning the string.

           yy_scan_string(const char *str)
                  scans a NUL-terminated string.

           yy_scan_bytes(const char *bytes, int len)
                  scans len bytes (including possibly NUL's) starting
                  at location bytes.

           Note  that  both of these functions create and scan a copy
           of the string or bytes.  (This  may  be  desirable,  since
           yylex()  modifies  the  contents of the buffer it is scan
           ning.)  You can avoid the copy by using:

           yy_scan_buffer(char *base, yy_size_t size)
                  which scans in place the buffer starting  at  base,
                  consisting  of  size  bytes,  the last two bytes of
                  which must be  YY_END_OF_BUFFER_CHAR  (ASCII  NUL).
                  These  last  two bytes are not scanned; thus, scan
                  ning  consists  of  base[0]  through  base[size-2],
                  inclusive.

                  If  you  fail  to set up base in this manner (i.e.,
                  forget the final two YY_END_OF_BUFFER_CHAR  bytes),
                  then yy_scan_buffer() returns a nil pointer instead
                  of creating a new input buffer.

                  The type yy_size_t is an integral type to which you
                  can  cast an integer expression reflecting the size
                  of the buffer.

## END-OF-FILE RULES

           The special rule "<<EOF>>" indicates actions which are  to
           be  taken  when an end-of-file is encountered and yywrap()
           returns non-zero (i.e., indicates no further files to pro
           cess).   The  action  must  finish  by  doing  one of four
           things:

           -      assigning yyin to a new  input  file  (in  previous
                  versions  of  flex,  after doing the assignment you
                  had to call the special action YY_NEW_FILE; this is
                  no longer necessary);

           -      executing a return statement;

           -      executing the special yyterminate() action;

           -      or,    switching    to    a    new   buffer   using
                  yy_switch_to_buffer()  as  shown  in  the   example
                  above.

           <<EOF>>  rules  may  not be used with other patterns; they

               ...other rules for dealing with quotes...

               <quote><<EOF>>   {
                        error( "unterminated quote" );
                        yyterminate();
                        }
               <<EOF>>  {
                        if ( *++filelist )
                            yyin = fopen( *filelist, "r" );
                        else
                           yyterminate();
                        }

## MISCELLANEOUS MACROS

           The  macro  YY_USER_ACTION  can  be  defined to provide an
           action which is  always  executed  prior  to  the  matched
           rule's action.  For example, it could be #define'd to call
           a  routine  to  convert  yytext   to   lower-case.    When
           YY_USER_ACTION  is  invoked, the variable yy_act gives the
           number of the matched rule (rules  are  numbered  starting
           with  1).   Suppose  you want to profile how often each of
           your rules is matched.  The following would do the trick:

               #define YY_USER_ACTION ++ctr[yy_act]

           where ctr is an array to hold the counts for the different
           rules.   Note  that the macro YY_NUM_RULES gives the total
           number of rules (including the default rule, even  if  you
           use -s), so a correct declaration for ctr is:

               int ctr[YY_NUM_RULES];

           The macro YY_USER_INIT may be defined to provide an action
           which is always executed before the first scan (and before
           the  scanner's  internal  initializations  are done).  For
           example, it could be used to call a routine to read  in  a
           data table or open a logging file.

           The  macro  yy_set_interactive(is_interactive) can be used
           to control whether the current buffer is considered inter
           active.   An  interactive buffer is processed more slowly,
           but must be used when the scanner's input source is indeed
           interactive  to  avoid  problems  due  to  waiting to fill
           buffers (see the discussion of the -I flag below).  A non-
           zero  value  in  the  macro invocation marks the buffer as
           interactive, a zero value as non-interactive.   Note  that
           use  of this macro overrides %option always-interactive or
           %option    never-interactive    (see    Options    below).
           yy_set_interactive() must be invoked prior to beginning to
           which may be  redefined.   By  default,  it  is  simply  a
           "break", to separate each rule's action from the following
           rule's.  Redefining  YY_BREAK  allows,  for  example,  C++
           users  to #define YY_BREAK to do nothing (while being very
           careful  that  every  rule  ends  with  a  "break"  or   a
           "return"!)  to  avoid suffering from unreachable statement
           warnings where because a rule's action ends with "return",
           the YY_BREAK is inaccessible.

## VALUES AVAILABLE TO THE USER

           This  section  summarizes  the various values available to
           the user in the rule actions.

           -      char *yytext holds the text of the  current  token.
                  It  may  be modified but not lengthened (you cannot
                  append characters to the end).

                  If the special  directive  %array  appears  in  the
                  first  section  of  the  scanner  description, then
                  yytext is  instead  declared  char  yytext[YYLMAX],
                  where  YYLMAX  is  a  macro definition that you can
                  redefine in the first section if you don't like the
                  default   value   (generally  8KB).   Using  %array
                  results in somewhat slower scanners, but the  value
                  of  yytext  becomes  immune to calls to input() and
                  unput(), which potentially destroy its  value  when
                  yytext  is  a  character  pointer.  The opposite of
                  %array is %pointer, which is the default.

                  You cannot use %array when generating  C++  scanner
                  classes (the -+ flag).

           -      int yyleng holds the length of the current token.

           -      FILE  *yyin is the file which by default flex reads
                  from.  It may be redefined but doing so only  makes
                  sense  before  scanning  begins or after an EOF has
                  been encountered.  Changing  it  in  the  midst  of
                  scanning  will  have  unexpected results since flex
                  buffers its input; use yyrestart()  instead.   Once
                  scanning terminates because an end-of-file has been
                  seen, you can assign yyin at the new input file and
                  then call the scanner again to continue scanning.

           -      void  yyrestart(  FILE *new_file ) may be called to
                  point yyin at the new input file.  The  switch-over
                  to  the  new  file  is  immediate  (any  previously
                  buffered-up input  is  lost).   Note  that  calling
                  yyrestart()  with  yyin  as an argument thus throws
                  away the current input buffer and  continues  scan
                  ning the same input file.

           named yylex() to find the next input token.   The  routine
           is  supposed  to return the type of the next token as well
           as putting any associated value in the global yylval.   To
           use flex with yacc, one specifies the -d option to yacc to
           instruct it to generate the file y.tab.h containing  defi
           nitions  of  all  the %tokens appearing in the yacc input.
           This file is then included in the flex scanner.  For exam
           ple,  if  one  of  the tokens is "TOK_NUMBER", part of the
           scanner might look like:

               %{
               #include "y.tab.h"
               %}

               %%

               [0-9]+        yylval = atoi( yytext ); return TOK_NUMBER;

## OPTIONS

           flex has the following options:

           -b     Generate  backing-up  information  to   lex.backup.
                  This  is  a  list  of  scanner states which require
                  backing up and the input characters on  which  they
                  do  so.   By adding rules one can remove backing-up
                  states.  If all backing-up  states  are  eliminated
                  and  -Cf or -CF is used, the generated scanner will
                  run faster (see the -p flag).  Only users who  wish
                  to  squeeze  every last cycle out of their scanners
                  need worry about this option.  (See the section  on
                  Performance Considerations below.)

           -c     is  a  do-nothing,  deprecated  option included for
                  POSIX compliance.

           -d     makes the generated  scanner  run  in  debug  mode.
                  Whenever  a  pattern  is  recognized and the global
                  yy_flex_debug is non-zero (which is  the  default),
                  the  scanner  will  write  to  stderr a line of the
                  form:

                      --accepting rule at line 53 ("the matched text")

                  The line number refers to the location of the  rule
                  in  the  file  defining the scanner (i.e., the file
                  that was fed to flex).  Messages are also generated
                  when  the  scanner  backs  up,  accepts the default
                  rule, reaches the  end  of  its  input  buffer  (or
                  encounters  a  NUL; at this point, the two look the
                  same as far as the scanner's concerned), or reaches
                  an end-of-file.
                  text given in yytext will have the  preserved  case
                  (i.e., it will not be folded).

           -l     turns  on  maximum  compatibility with the original
                  AT&T lex implementation.  Note that this  does  not
                  mean  full compatibility.  Use of this option costs
                  a considerable amount of performance, and it cannot
                  be  used  with the -+, -f, -F, -Cf, or -CF options.
                  For details on the compatibilities it provides, see
                  the  section "Incompatibilities With Lex And POSIX"
                  below.   This  option  also  results  in  the  name
                  YY_FLEX_LEX_COMPAT being #define'd in the generated
                  scanner.

           -n     is another do-nothing, deprecated  option  included
                  only for POSIX compliance.

           -p     generates  a  performance  report  to  stderr.  The
                  report consists of comments regarding  features  of
                  the flex input file which will cause a serious loss
                  of performance in the resulting  scanner.   If  you
                  give  the  flag  twice,  you will also get comments
                  regarding features that lead to  minor  performance
                  losses.

                  Note  that the use of REJECT, %option yylineno, and
                  variable trailing context (see the  Deficiencies  /
                  Bugs  section  below) entails a substantial perfor
                  mance penalty; use of yymore(), the ^ operator, and
                  the -I flag entail minor performance penalties.

           -s     causes  the  default  rule  (that unmatched scanner
                  input is echoed to stdout) to  be  suppressed.   If
                  the  scanner  encounters  input that does not match
                  any of its rules, it aborts with  an  error.   This
                  option  is  useful for finding holes in a scanner's
                  rule set.

           -t     instructs flex to write the scanner it generates to
                  standard output instead of lex.yy.c.

           -v     specifies  that  flex should write to stderr a sum
                  mary of statistics regarding the scanner it  gener
                  ates.   Most  of  the statistics are meaningless to
                  the casual flex user, but the first line identifies
                  the  version  of flex (same as reported by -V), and
                  the next line the flags used  when  generating  the
                  scanner, including those that are on by default.

           -w     suppresses warning messages.

           -B     instructs  flex  to  generate  a batch scanner, the
                  larger).  In general, if the pattern  set  contains
                  both "keywords" and a catch-all, "identifier" rule,
                  such as in the set:

                      "case"    return TOK_CASE;
                      "switch"  return TOK_SWITCH;
                      ...
                      "default" return TOK_DEFAULT;
                      [a-z]+    return TOK_ID;

                  then you're better off using the full table  repre
                  sentation.   If  only the "identifier" rule is pre
                  sent and you then use a hash table or some such  to
                  detect the keywords, you're better off using -F.

                  This  option is equivalent to -CFr (see below).  It
                  cannot be used with -+.

           -I     instructs flex to generate an interactive  scanner.
                  An interactive scanner is one that only looks ahead
                  to decide what token has been matched if  it  abso
                  lutely  must.  It turns out that always looking one
                  extra character ahead,  even  if  the  scanner  has
                  already  seen  enough text to disambiguate the cur
                  rent token, is a bit faster than only looking ahead
                  when  necessary.   But  scanners  that  always look
                  ahead give dreadful  interactive  performance;  for
                  example,  when  a  user  types a newline, it is not
                  recognized as a  newline  token  until  they  enter
                  another  token, which often means typing in another
                  whole line.

                  Flex scanners default to interactive unless you use
                  the  -Cf  or  -CF  table-compression  options  (see
                  below).  That's because if you're looking for high-
                  performance  you  should  be  using  one  of  these
                  options, so  if  you  didn't,  flex  assumes  you'd
                  rather  trade off a bit of run-time performance for
                  intuitive interactive behavior.  Note also that you
                  cannot  use  -I  in  conjunction  with  -Cf or -CF.
                  Thus, this option is not really needed; it is on by
                  default for all those cases in which it is allowed.

                  You can force a scanner to not  be  interactive  by
                  using -B (see above).

           -L     instructs  flex  not  to generate #line directives.
                  Without this option,  flex  peppers  the  generated
                  scanner  with #line directives so error messages in
                  the actions will be correctly located with  respect
                  to  either  the  original  flex  input file (if the
                  errors are due to  code  in  the  input  file),  or
                  one  which  can only recognized 7-bit characters in
                  its input.  The advantage of using -7 is  that  the
                  scanner's  tables  can  be  up  to half the size of
                  those generated using the -8  option  (see  below).
                  The  disadvantage  is that such scanners often hang
                  or crash if their input contains an  8-bit  charac
                  ter.

                  Note,  however, that unless you generate your scan
                  ner using the -Cf or -CF table compression options,
                  use  of  -7  will save only a small amount of table
                  space, and  make  your  scanner  considerably  less
                  portable.   Flex's  default behavior is to generate
                  an 8-bit scanner unless you use the -Cf or -CF,  in
                  which  case flex defaults to generating 7-bit scan
                  ners unless your site was always configured to gen
                  erate  8-bit  scanners  (as  will often be the case
                  with non-USA sites).  You  can  tell  whether  flex
                  generated a 7-bit or an 8-bit scanner by inspecting
                  the flag summary in  the  -v  output  as  described
                  above.

                  Note that if you use -Cfe or -CFe (those table com
                  pression  options,  but  also   using   equivalence
                  classes   as   discussed  see  below),  flex  still
                  defaults to generating an 8-bit scanner, since usu
                  ally  with  these  compression  options  full 8-bit
                  tables are  not  much  more  expensive  than  7-bit
                  tables.

           -8     instructs  flex to generate an 8-bit scanner, i.e.,
                  one which can  recognize  8-bit  characters.   This
                  flag  is  only  needed for scanners generated using
                  -Cf or -CF, as otherwise flex defaults to  generat
                  ing an 8-bit scanner anyway.

                  See  the  discussion of -7 above for flex's default
                  behavior and the tradeoffs between 7-bit and  8-bit
                  scanners.

           -+     specifies  that  you  want  flex  to generate a C++
                  scanner class.  See the section on  Generating  C++
                  Scanners below for details.

           -C[aefFmr]
                  controls  the degree of table compression and, more
                  generally, trade-offs between  small  scanners  and
                  fast scanners.

                  -Ca  ("align")  instructs  flex to trade off larger
                  tables in the generated scanner for faster  perfor
                  mance because the elements of the tables are better
                  cally a factor of 2-5) and are pretty cheap perfor
                  mance-wise   (one   array   look-up  per  character
                  scanned).

                  -Cf specifies that the full scanner  tables  should
                  be  generated - flex should not compress the tables
                  by taking advantages of  similar  transition  func
                  tions for different states.

                  -CF  specifies that the alternate fast scanner rep
                  resentation (described above  under  the  -F  flag)
                  should  be  used.   This option cannot be used with
                  -+.

                  -Cm  directs  flex  to  construct  meta-equivalence
                  classes,  which are sets of equivalence classes (or
                  characters, if equivalence classes  are  not  being
                  used) that are commonly used together.  Meta-equiv
                  alence classes are often a big win when using  com
                  pressed  tables,  but  they have a moderate perfor
                  mance impact (one or two "if" tests and  one  array
                  look-up per character scanned).

                  -Cr  causes  the generated scanner to bypass use of
                  the  standard  I/O  library  (stdio)   for   input.
                  Instead  of  calling fread() or getc(), the scanner
                  will use the read() system  call,  resulting  in  a
                  performance  gain  which varies from system to sys
                  tem, but in general is probably  negligible  unless
                  you are also using -Cf or -CF.  Using -Cr can cause
                  strange behavior if, for  example,  you  read  from
                  yyin  using  stdio  prior  to  calling  the scanner
                  (because the scanner will miss whatever  text  your
                  previous reads left in the stdio input buffer).

                  -Cr  has  no effect if you define YY_INPUT (see The
                  Generated Scanner above).

                  A lone -C specifies that the scanner tables  should
                  be  compressed  but neither equivalence classes nor
                  meta-equivalence classes should be used.

                  The options -Cf or -CF and -Cm do  not  make  sense
                  together - there is no opportunity for meta-equiva
                  lence classes if the table is not being compressed.
                  Otherwise  the options may be freely mixed, and are
                  cumulative.

                  The default setting is -Cem, which  specifies  that
                  flex  should generate equivalence classes and meta-
                  equivalence classes.   This  setting  provides  the
                  highest degree of table compression.  You can trade
                  usually generated and  compiled  the  quickest,  so
                  during development you will usually want to use the
                  default, maximal compression.

                  -Cfe is often a good compromise between  speed  and
                  size for production scanners.

           -ooutput
                  directs  flex to write the scanner to the file out
                  put instead of lex.yy.c.  If you  combine  -o  with
                  the  -t option, then the scanner is written to std
                  out but its #line directives  (see  the  -L  option
                  above) refer to the file output.

           -Pprefix
                  changes  the default yy prefix used by flex for all
                  globally-visible variable  and  function  names  to
                  instead  be prefix.  For example, -Pfoo changes the
                  name of yytext to footext.   It  also  changes  the
                  name  of  the  default output file from lex.yy.c to
                  lex.foo.c.  Here are all of the names affected:

                      yy_create_buffer
                      yy_delete_buffer
                      yy_flex_debug
                      yy_init_buffer
                      yy_flush_buffer
                      yy_load_buffer_state
                      yy_switch_to_buffer
                      yyin
                      yyleng
                      yylex
                      yylineno
                      yyout
                      yyrestart
                      yytext
                      yywrap

                  (If you are using a C++ scanner, then  only  yywrap
                  and yyFlexLexer are affected.)  Within your scanner
                  itself, you can still refer to the global variables
                  and  functions  using either version of their name;
                  but externally, they have the modified name.

                  This option lets you easily link together  multiple
                  flex  programs  into  the  same  executable.  Note,
                  though,  that  using  this  option   also   renames
                  yywrap(),  so  you now must either provide your own
                  (appropriately-named) version of  the  routine  for
                  your  scanner,  or use %option noyywrap, as linking
                  with  -lfl  no  longer  provides  one  for  you  by
                  default.

           Most options are given simply as  names,  optionally  pre
           ceded by the word "no" (with no intervening whitespace) to
           negate their meaning.  A number  are  equivalent  to  flex
           flags or their negation:

               7bit            -7 option
               8bit            -8 option
               align           -Ca option
               backup          -b option
               batch           -B option
               c++             -+ option

               caseful or
               case-sensitive  opposite of -i (default)

               case-insensitive or
               caseless        -i option

               debug           -d option
               default         opposite of -s option
               ecs             -Ce option
               fast            -F option
               full            -f option
               interactive     -I option
               lex-compat      -l option
               meta-ecs        -Cm option
               perf-report     -p option
               read            -Cr option
               stdout          -t option
               verbose         -v option
               warn            opposite of -w option
                               (use "%option nowarn" for -w)

               array           equivalent to "%array"
               pointer         equivalent to "%pointer" (default)

           Some %option's provide features otherwise not available:

           always-interactive
                  instructs  flex  to generate a scanner which always
                  considers its input  "interactive".   Normally,  on
                  each  new  input file the scanner calls isatty() in
                  an attempt to determine whether the scanner's input
                  source  is  interactive  and  thus should be read a
                  character at a time.  When  this  option  is  used,
                  however, then no such call is made.

           main   directs  flex  to  provide a default main() program
                  for the scanner, which simply calls yylex().   This
                  option implies noyywrap (see below).

                  C,  which  does  not require stdin and stdout to be
                  compile-time constant.

           yylineno
                  directs flex to generate a scanner  that  maintains
                  the  number of the current line read from its input
                  in the global variable yylineno.   This  option  is
                  implied by %option lex-compat.

           yywrap if  unset (i.e., %option noyywrap), makes the scan
                  ner not call yywrap() upon an end-of-file, but sim
                  ply  assume  that  there  are no more files to scan
                  (until the user points yyin at a new file and calls
                  yylex() again).

           flex  scans your rule actions to determine whether you use
           the REJECT or yymore() features.  The  reject  and  yymore
           options  are  available  to  override  its  decision as to
           whether you use the options, either by setting them (e.g.,
           %option reject) to indicate the feature is indeed used, or
           unsetting them to indicate it actually is not used  (e.g.,
           %option noyymore).

           Three  options  take  string-delimited values, offset with
           '=':

               %option outfile="ABC"

           is equivalent to -oABC, and

               %option prefix="XYZ"

           is equivalent to -PXYZ.  Finally,

               %option yyclass="foo"

           only applies when generating a C++ scanner (  -+  option).
           It informs flex that you have derived foo as a subclass of
           yyFlexLexer, so flex will place your actions in the member
           function foo::yylex() instead of yyFlexLexer::yylex().  It
           also generates a yyFlexLexer::yylex() member function that
           emits  a  run-time  error (by invoking yyFlexLexer::Lexer
           Error()) if called.  See Generating C++  Scanners,  below,
           for additional information.

           A  number  of  options  are available for lint purists who
           want to suppress the appearance of  unneeded  routines  in
           the  generated  scanner.   Each of the following, if unset
           (e.g., %option nounput ),  results  in  the  corresponding
           routine not appearing in the generated scanner:

               input, unput
               REJECT
               %option yylineno
               arbitrary trailing context

               pattern sets that require backing up
               %array
               %option interactive
               %option always-interactive

               '^' beginning-of-line operator
               yymore()

           with  the  first  three  all being quite expensive and the
           last two being quite cheap.  Note  also  that  unput()  is
           implemented  as a routine call that potentially does quite
           a bit of work, while yyless() is a quite-cheap  macro;  so
           if  just  putting  back  some excess text you scanned, use
           yyless().

           REJECT should be avoided at all costs when performance  is
           important.  It is a particularly expensive option.

           Getting  rid  of  backing  up is messy and often may be an
           enormous amount of work for  a  complicated  scanner.   In
           principal,  one  begins by using the -b flag to generate a
           lex.backup file.  For example, on the input

               %%
               foo        return TOK_KEYWORD;
               foobar     return TOK_KEYWORD;

           the file looks like:

               State #6 is non-accepting -
                associated rule line numbers:
                      2       3
                out-transitions: [ o ]
                jam-transitions: EOF [ \001-n  p-\177 ]

               State #8 is non-accepting -
                associated rule line numbers:
                      3
                out-transitions: [ a ]
                jam-transitions: EOF [ \001-`  b-\177 ]

               State #9 is non-accepting -
                associated rule line numbers:
                      3
                out-transitions: [ r ]
                jam-transitions: EOF [ \001-q  s-\177 ]

               Compressed tables always back up.

           The comment regarding State #8 indicates there's a problem
           when  "foob"  has  been scanned.  Indeed, on any character
           other than an 'a', the scanner will have  to  back  up  to
           accept  "foo".   Similarly,  the comment for State #9 con
           cerns when "fooba" has been scanned and an  'r'  does  not
           follow.

           The  final  comment reminds us that there's no point going
           to all the trouble of removing backing up from  the  rules
           unless  we're  using  -Cf or -CF, since there's no perfor
           mance gain doing so with compressed scanners.

           The way to remove the backing up is to add "error" rules:

               %%
               foo         return TOK_KEYWORD;
               foobar      return TOK_KEYWORD;

               fooba       |
               foob        |
               fo          {
                           /* false alarm, not really a keyword */
                           return TOK_ID;
                           }

           Eliminating backing up among a list of keywords  can  also
           be done using a "catch-all" rule:

               %%
               foo         return TOK_KEYWORD;
               foobar      return TOK_KEYWORD;

               [a-z]+      return TOK_ID;

           This is usually the best solution when appropriate.

           Backing  up  messages tend to cascade.  With a complicated
           set of rules it's not uncommon to  get  hundreds  of  mes
           sages.   If  one  can decipher them, though, it often only
           takes a dozen or so rules  to  eliminate  the  backing  up
           (though it's easy to make a mistake and have an error rule
           accidentally match a valid token.  A possible future  flex
           feature  will  be  to automatically add rules to eliminate
           backing up).

           It's important to keep in mind that you gain the  benefits
           of  eliminating  backing  up  only  if you eliminate every
           instance of backing up.  Leaving just one means  you  gain
           nothing.

           or as

               %%
               mouse|rat/cat         run();
               mouse|rat/dog         run();

           Note that here the special '|' action does not provide any
           savings,  and can even make things worse (see Deficiencies
           / Bugs below).

           Another area where the user can increase a scanner's  per
           formance  (and one that's easier to implement) arises from
           the fact that the longer the tokens  matched,  the  faster
           the  scanner  will  run.  This is because with long tokens
           the processing of most input characters takes place in the
           (short) inner scanning loop, and does not often have to go
           through the additional work of  setting  up  the  scanning
           environment  (e.g.,  yytext)  for  the action.  Recall the
           scanner for C comments:

               %x comment
               %%
                       int line_num = 1;

               "/*"         BEGIN(comment);

               <comment>[^*\n]*
               <comment>"*"+[^*/\n]*
               <comment>\n             ++line_num;
               <comment>"*"+"/"        BEGIN(INITIAL);

           This could be sped up by writing it as:

               %x comment
               %%
                       int line_num = 1;

               "/*"         BEGIN(comment);

               <comment>[^*\n]*
               <comment>[^*\n]*\n      ++line_num;
               <comment>"*"+[^*/\n]*
               <comment>"*"+[^*/\n]*\n ++line_num;
               <comment>"*"+"/"        BEGIN(INITIAL);

           Now instead of each newline requiring  the  processing  of
           another  action, recognizing the newlines is "distributed"
           over the other rules to keep the matched text as  long  as
           possible.   Note  that adding rules does not slow down the
           scanner!  The speed of the scanner is independent  of  the
           number of rules or (modulo the considerations given at the
           beginning of this section) how complicated the  rules  are
               while    /* it's a keyword */

               .|\n     /* it's not a keyword */

           To  eliminate  the  back-tracking,  introduce  a catch-all
           rule:

               %%
               asm      |
               auto     |
               break    |
               ... etc ...
               volatile |
               while    /* it's a keyword */

               [a-z]+   |
               .|\n     /* it's not a keyword */

           Now, if it's guaranteed that there's exactly one word  per
           line,  then we can reduce the total number of matches by a
           half by merging in the recognition of newlines  with  that
           of the other tokens:

               %%
               asm\n    |
               auto\n   |
               break\n  |
               ... etc ...
               volatile\n |
               while\n  /* it's a keyword */

               [a-z]+\n |
               .|\n     /* it's not a keyword */

           One  has  to  be careful here, as we have now reintroduced
           backing up into the scanner.  In particular, while we know
           that  there  will  never  be  any  characters in the input
           stream other than letters or newlines, flex  can't  figure
           this out, and it will plan for possibly needing to back up
           when it has scanned a token like "auto" and then the  next
           character  is  something other than a newline or a letter.
           Previously it would then just match the "auto" rule and be
           done, but now it has no "auto" rule, only a "auto\n" rule.
           To eliminate the  possibility  of  backing  up,  we  could
           either duplicate all rules but without final newlines, or,
           since we never expect  to  encounter  such  an  input  and
           therefore  don't how it's classified, we can introduce one
           more catch-all rule, this one which doesn't include a new
           line:

               %%
               asm\n    |

           larly  when a token contains multiple NUL's.  It's best to
           write rules which match short  amounts  of  text  if  it's
           anticipated that the text will often include NUL's.

           Another  final  note  regarding  performance: as mentioned
           above in the section How the Input is Matched, dynamically
           resizing  yytext to accommodate huge tokens is a slow pro
           cess because it presently requires that the  (huge)  token
           be  rescanned  from the beginning.  Thus if performance is
           vital, you should attempt to match "large"  quantities  of
           text  but  not "huge" quantities, where the cutoff between
           the two is at about 8K characters/token.

## GENERATING C++ SCANNERS

           flex provides two different ways to generate scanners  for
           use  with C++.  The first way is to simply compile a scan
           ner generated by flex using a C++ compiler instead of a  C
           compiler.   You  should  not  encounter  any  compilations
           errors (please report any you find to  the  email  address
           given  in the Author section below).  You can then use C++
           code in your rule actions instead of C  code.   Note  that
           the  default  input  source for your scanner remains yyin,
           and default echoing is still done to yyout.  Both of these
           remain FILE * variables and not C++ streams.

           You  can  also  use  flex to generate a C++ scanner class,
           using the -+ option (or, equivalently, %option c++), which
           is  automatically  specified  if the name of the flex exe
           cutable ends in a '+', such as flex++.   When  using  this
           option,  flex  defaults  to  generating the scanner to the
           file lex.yy.cc instead of lex.yy.c.  The generated scanner
           includes  the  header  file FlexLexer.h, which defines the
           interface to two C++ classes.

           The first class,  FlexLexer,  provides  an  abstract  base
           class  defining  the  general scanner class interface.  It
           provides the following member functions:

           const char* YYText()
                  returns the  text  of  the  most  recently  matched
                  token, the equivalent of yytext.

           int YYLeng()
                  returns  the  length  of  the most recently matched
                  token, the equivalent of yyleng.

           int lineno() const
                  returns the current input line number (see  %option
                  yylineno), or 1 if %option yylineno was not used.

           void set_debug( int flag )
                  sets the debugging flag for the scanner, equivalent

           The  second  class  defined in FlexLexer.h is yyFlexLexer,
           which is derived from FlexLexer.  It defines the following
           additional member functions:

           yyFlexLexer( istream* arg_yyin = 0, ostream* arg_yyout = 0
           )
                  constructs  a  yyFlexLexer  object  using the given
                  streams for input and output.   If  not  specified,
                  the  streams default to cin and cout, respectively.

           virtual int yylex()
                  performs the same role is yylex() does for ordinary
                  flex scanners: it scans the input stream, consuming
                  tokens, until a rule's action returns a value.   If
                  you  derive  a subclass S from yyFlexLexer and want
                  to access the member functions and variables  of  S
                  inside  yylex(),  then  you  need  to  use  %option
                  yyclass="S" to inform flex that you will  be  using
                  that  subclass  instead  of  yyFlexLexer.   In this
                  case, rather than generating  yyFlexLexer::yylex(),
                  flex  generates  S::yylex()  (and  also generates a
                  dummy     yyFlexLexer::yylex()      that      calls
                  yyFlexLexer::LexerError() if called).

           virtual void switch_streams(istream* new_in = 0,
                  ostream*  new_out = 0) reassigns yyin to new_in (if
                  non-nil) and yyout to new_out (ditto), deleting the
                  previous input buffer if yyin is reassigned.

           int yylex( istream* new_in, ostream* new_out = 0 )
                  first    switches    the    input    streams    via
                  switch_streams( new_in, new_out ) and then  returns
                  the value of yylex().

           In  addition,  yyFlexLexer defines the following protected
           virtual  functions  which  you  can  redefine  in  derived
           classes to tailor the scanner:

           virtual int LexerInput( char* buf, int max_size )
                  reads  up  to  max_size  characters  into  buf  and
                  returns the number of characters read.  To indicate
                  end-of-input,   return  0  characters.   Note  that
                  "interactive" scanners (see the -B  and  -I  flags)
                  define  the  macro YY_INTERACTIVE.  If you redefine
                  LexerInput() and need  to  take  different  actions
                  depending  on  whether  or not the scanner might be
                  scanning an interactive input source, you can  test
                  for the presence of this name via #ifdef.

           virtual void LexerOutput( const char* buf, int size )
                  writes  out  size  characters  from the buffer buf,

           using the -P option discussed above.

           Finally,  note that the %array feature is not available to
           C++ scanner classes; you must use %pointer (the  default).

           Here is an example of a simple C++ scanner:

                   // An example of using the flex C++ scanner class.

               %{
               int mylineno = 0;
               %}

               string  \"[^\n"]+\"

               ws      [ \t]+

               alpha   [A-Za-z]
               dig     [0-9]
               name    ({alpha}|{dig}|\$)({alpha}|{dig}|[_.\-/$])*
               num1    [-+]?{dig}+\.?([eE][-+]?{dig}+)?
               num2    [-+]?{dig}*\.{dig}+([eE][-+]?{dig}+)?
               number  {num1}|{num2}

               %%

               {ws}    /* skip blanks and tabs */

               "/*"    {
                       int c;

                       while((c = yyinput()) != 0)
                           {
                           if(c == '\n')
                               ++mylineno;

                           else if(c == '*')
                               {
                               if((c = yyinput()) == '/')
                                   break;
                               else
                                   unput(c);
                               }
                           }
                       }

               {number}  cout << "number " << YYText() << '\n';

               \n        mylineno++;

               {name}    cout << "name " << YYText() << '\n';

           include <FlexLexer.h> in your other sources once per lexer
           class, first renaming yyFlexLexer as follows:

               #undef yyFlexLexer
               #define yyFlexLexer xxFlexLexer
               #include <FlexLexer.h>

               #undef yyFlexLexer
               #define yyFlexLexer zzFlexLexer
               #include <FlexLexer.h>

           if,  for  example, you used %option prefix="xx" for one of
           your scanners and %option prefix="zz" for the other.

           IMPORTANT: the present  form  of  the  scanning  class  is
           experimental  and  may  change  considerably between major
           releases.

## INCOMPATIBILITIES WITH LEX AND POSIX

           flex is a rewrite of the  AT&T  Unix  lex  tool  (the  two
           implementations  do not share any code, though), with some
           extensions and incompatibilities, both  of  which  are  of
           concern  to those who wish to write scanners acceptable to
           either implementation.  Flex is fully compliant  with  the
           POSIX  lex  specification, except that when using %pointer
           (the default), a call to unput() destroys the contents  of
           yytext, which is counter to the POSIX specification.

           In  this  section  we  discuss  all  of the known areas of
           incompatibility between flex,  AT&T  lex,  and  the  POSIX
           specification.

           flex's  -l  option turns on maximum compatibility with the
           original AT&T lex implementation, at the cost of  a  major
           loss  in  the  generated  scanner's  performance.  We note
           below which incompatibilities can be overcome using the -l
           option.

           flex  is  fully  compatible  with  lex  with the following
           exceptions:

           -      The  undocumented  lex  scanner  internal  variable
                  yylineno  is  not  supported  unless  -l or %option
                  yylineno is used.

                  yylineno  should  be  maintained  on  a  per-buffer
                  basis,  rather  than  a  per-scanner (single global
                  variable) basis.

                  yylineno is not part of the POSIX specification.

           -      The input() routine is not redefinable,  though  it

           -      The  unput()  routine  is  not  redefinable.   This
                  restriction is in accordance with POSIX.

           -      flex scanners are not as reentrant as lex scanners.
                  In particular, if you have an  interactive  scanner
                  and  an  interrupt  handler which long-jumps out of
                  the scanner, and the scanner is subsequently called
                  again, you may get the following message:

                      fatal flex scanner internal error--end of buffer missed

                  To reenter the scanner, first use

                      yyrestart( yyin );

                  Note  that  this  call will throw away any buffered
                  input; usually this isn't a problem with an  inter
                  active scanner.

                  Also  note  that flex C++ scanner classes are reen
                  trant, so if using C++ is an option  for  you,  you
                  should use them instead.  See "Generating C++ Scan
                  ners" above for details.

           -      output() is not supported.  Output  from  the  ECHO
                  macro  is  done  to the file-pointer yyout (default
                  stdout).

                  output() is not part of the POSIX specification.

           -      lex does not  support  exclusive  start  conditions
                  (%x), though they are in the POSIX specification.

           -      When  definitions  are expanded, flex encloses them
                  in parentheses.  With lex, the following:

                      NAME    [A-Z][A-Z0-9]*
                      %%
                      foo{NAME}?      printf( "Found it\n" );
                      %%

                  will not match the string "foo"  because  when  the
                  macro is expanded the rule is equivalent to "foo[A-
                  Z][A-Z0-9]*?"  and the precedence is such that  the
                  '?' is associated with "[A-Z0-9]*".  With flex, the
                  rule will be expanded to "foo([A-Z][A-Z0-9]*)?" and
                  so the string "foo" will match.

                  Note  that  if the definition begins with ^ or ends
                  with $ then it is not expanded with parentheses, to
                  allow  these  operators  to  appear  in definitions
                      %%
                      foo|bar<space here>
                        { foobar_action(); }

                  flex does not support this feature.

           -      The lex %r (generate a Ratfor  scanner)  option  is
                  not  supported.  It is not part of the POSIX speci
                  fication.

           -      After a call to unput(), yytext is undefined  until
                  the  next  token is matched, unless the scanner was
                  built using %array.  This is not the case with  lex
                  or  the  POSIX  specification.   The -l option does
                  away with this incompatibility.

           -      The precedence of the {} (numeric  range)  operator
                  is  different.  lex interprets "abc{1,3}" as "match
                  one, two, or three occurrences of  'abc'",  whereas
                  flex  interprets it as "match 'ab' followed by one,
                  two, or three occurrences of 'c'".  The  latter  is
                  in agreement with the POSIX specification.

           -      The precedence of the ^ operator is different.  lex
                  interprets "^foo|bar" as "match either 'foo' at the
                  beginning  of  a  line, or 'bar' anywhere", whereas
                  flex interprets it as "match either 'foo' or  'bar'
                  if they come at the beginning of a line".  The lat
                  ter is in agreement with the POSIX specification.

           -      The special table-size declarations such as %a sup
                  ported  by  lex  are not required by flex scanners;
                  flex ignores them.

           -      The name FLEX_SCANNER is #define'd so scanners  may
                  be  written for use with either flex or lex.  Scan
                  ners   also   include   YY_FLEX_MAJOR_VERSION   and
                  YY_FLEX_MINOR_VERSION  indicating  which version of
                  flex generated the scanner (for  example,  for  the
                  2.5 release, these defines would be 2 and 5 respec
                  tively).

           The following flex features are not included in lex or the
           POSIX specification:

               C++ scanners
               %option
               start condition scopes
               start condition stacks
               interactive/non-interactive scanners
               yy_scan_string() and friends
               yyterminate()

           the list refers to the fact that with  flex  you  can  put
           multiple  actions  on  the same line, separated with semi-
           colons, while with lex, the following

               foo    handle_foo(); ++num_foos_seen;

           is (rather surprisingly) truncated to

               foo    handle_foo();

           flex does not truncate the action.  Actions that  are  not
           enclosed in braces are simply terminated at the end of the
           line.

## DIAGNOSTICS

           warning, rule cannot be matched indicates that  the  given
           rule cannot be matched because it follows other rules that
           will always match the same text as it.   For  example,  in
           the  following  "foo"  cannot  be matched because it comes
           after an identifier "catch-all" rule:

               [a-z]+    got_identifier();
               foo       got_foo();

           Using REJECT in a scanner suppresses this warning.

           warning, -s option given but default rule can  be  matched
           means  that  it  is possible (perhaps only in a particular
           start condition) that the default rule (match  any  single
           character)  is  the  only one that will match a particular
           input.   Since  -s  was  given,  presumably  this  is  not
           intended.

           reject_used_but_not_detected          undefined         or
           yymore_used_but_not_detected undefined - These errors  can
           occur  at  compile  time.   They indicate that the scanner
           uses REJECT or yymore() but that flex failed to notice the
           fact,  meaning  that  flex  scanned the first two sections
           looking for occurrences of these  actions  and  failed  to
           find  any,  but  somehow you snuck some in (via a #include
           file, for example).  Use %option reject or %option  yymore
           to indicate to flex that you really do use these features.

           flex scanner jammed -  a  scanner  compiled  with  -s  has
           encountered an input string which wasn't matched by any of
           its rules.  This error can  also  occur  due  to  internal
           problems.

           token too large, exceeds YYLMAX - your scanner uses %array
           and one of its rules matched a string longer than the YYL
           MAX  constant (8K bytes by default).  You can increase the
           value by #define'ing YYLMAX in the definitions section  of

           input buffer overflow, can't enlarge buffer because  scan
           ner  uses  REJECT - the scanner was working on matching an
           extremely large token  and  needed  to  expand  the  input
           buffer.   This doesn't work with scanners that use REJECT.

           fatal flex scanner internal error--end of buffer missed  -
           This  can  occur  in an scanner which is reentered after a
           long-jump has jumped out (or over) the  scanner's  activa
           tion frame.  Before reentering the scanner, use:

               yyrestart( yyin );

           or, as noted above, switch to using the C++ scanner class.

           too many start conditions in <> construct!  -  you  listed
           more start conditions in a <> construct than exist (so you
           must have listed at least one of them twice).

## FILES

           -lfl   library with which scanners must be linked.

           lex.yy.c
                  generated scanner (called lexyy.c on some systems).

           lex.yy.cc
                  generated C++ scanner class, when using -+.

           <FlexLexer.h>
                  header  file  defining  the C++ scanner base class,
                  FlexLexer, and its derived class, yyFlexLexer.

           flex.skl
                  skeleton scanner.  This  file  is  only  used  when
                  building flex, not when flex executes.

           lex.backup
                  backing-up  information for -b flag (called lex.bck
                  on some systems).

## DEFICIENCIES / BUGS

           Some trailing context patterns cannot be properly  matched
           and  generate  warning  messages ("dangerous trailing con
           text").  These are patterns where the ending of the  first
           part of the rule matches the beginning of the second part,
           such as "zx*/xy*", where the 'x*' matches the 'x'  at  the
           beginning  of  the trailing context.  (Note that the POSIX
           draft states that the text matched  by  such  patterns  is
           undefined.)

           For  some trailing context rules, parts which are actually
           fixed-length are not recognized as such,  leading  to  the
           Use of unput() invalidates yytext and yyleng,  unless  the
           %array directive or the -l option has been used.

           Pattern-matching  of  NUL's  is  substantially slower than
           matching other characters.

           Dynamic resizing of  the  input  buffer  is  slow,  as  it
           entails rescanning all the text matched so far by the cur
           rent (generally huge) token.

           Due to both buffering of input and read-ahead, you  cannot
           intermix  calls  to <stdio.h> routines, such as, for exam
           ple, getchar(), with flex rules and  expect  it  to  work.
           Call input() instead.

           The total table entries listed by the -v flag excludes the
           number of table entries needed to determine what rule  has
           been  matched.  The number of entries is equal to the num
           ber of DFA states if the scanner does not use REJECT,  and
           somewhat greater than the number of states if it does.

           REJECT cannot be used with the -f or -F options.

           The flex internal algorithms need documentation.

## SEE ALSO

           lex(1), yacc(1), sed(1), awk(1).

           John  Levine,  Tony  Mason,  and  Doug  Brown, Lex & Yacc,
           O'Reilly and Associates.  Be sure to get the 2nd  edition.

           M.  E. Lesk and E. Schmidt, LEX - Lexical Analyzer Genera
           tor

           Alfred Aho, Ravi  Sethi  and  Jeffrey  Ullman,  Compilers:
           Principles,  Techniques  and Tools, Addison-Wesley (1986).
           Describes the pattern-matching  techniques  used  by  flex
           (deterministic finite automata).

## AUTHOR

           Vern Paxson, with the help of many ideas and much inspira
           tion  from  Van  Jacobson.   Original   version   by   Jef
           Poskanzer.   The  fast  table  representation is a partial
           implementation of a design  done  by  Van  Jacobson.   The
           implementation was done by Kevin Gong and Vern Paxson.

           Thanks  to  the  many  flex beta-testers, feedbackers, and
           contributors, especially Francois  Pinard,  Casey  Leedom,
           Robert  Abramovitz,  Stan  Adermann,  Terry  Allen,  David
           Barker-Plummer, John  Basrai,  Neal  Becker,  Nelson  H.F.
           Beebe,  benson@odi.com,  Karl Berry, Peter A. Bigot, Simon
           Blanchard, Keith Bostic, Frederic  Brehm,  Ian  Brockbank,
           Lenard, Craig Leres, John Levine, Steve Liddle, David Lof
           fredo, Mike Long, Mohamed el Lozy,  Brian  Madsen,  Malte,
           Joe  Marshall,  Bengt Martensson, Chris Metcalf, Luke Mew
           burn, Jim Meyering, R. Alexander  Milowski,  Erik  Naggum,
           G.T.  Nicol,  Landon  Noll,  James  Nordby,  Marc  Nozell,
           Richard Ohnemus, Karsten Pahnke, Sven Panne, Roland Pesch,
           Walter   Pelissero,   Gaumond  Pierre,  Esmond  Pitt,  Jef
           Poskanzer, Joe Rahmeh, Jarmo  Raiha,  Frederic  Raimbault,
           Pat  Rankin,  Rick Richardson, Kevin Rodgers, Kai Uwe Rom
           mel, Jim Roskind, Alberto Santini, Andreas  Scherer,  Dar
           rell Schiebel, Raf Schietekat, Doug Schmidt, Philippe Sch
           noebelen, Andreas Schwab, Larry  Schwimmer,  Alex  Siegel,
           Eckehard Stolz, Jan-Erik Strvmquist, Mike Stump, Paul Stu
           art,  Dave  Tallman,  Ian  Lance  Taylor,  Chris  Thewalt,
           Richard  M.  Timoney, Jodi Tsai, Paul Tuinenga, Gary Weik,
           Frank Whaley, Gerhard Wilhelms, Kent  Williams,  Ken  Yap,
           Ron  Zellar,  Nathan  Zelle,  David  Zuhn, and those whose
           names have slipped my marginal mail-archiving  skills  but
           whose contributions are appreciated all the same.

           Thanks  to  Keith Bostic, Jon Forrest, Noah Friedman, John
           Gilmore, Craig  Leres,  John  Levine,  Bob  Mulcahy,  G.T.
           Nicol,  Francois  Pinard,  Rich Salz, and Richard Stallman
           for help with various distribution headaches.

           Thanks to Esmond Pitt and Earle Horton for 8-bit character
           support;  to  Benson Margulies and Fred Burke for C++ sup
           port; to Kent Williams and Tom Epperly for C++ class  sup
           port;  to  Ove  Ewerlid  for support of NUL's; and to Eric
           Hughes for support of multiple buffers.

           This work was primarily done when I was with the Real Time
           Systems  Group  at  the  Lawrence  Berkeley  Laboratory in
           Berkeley, CA.  Many thanks to all there for the support  I
           received.

           Send comments to vern@ee.lbl.gov.

    Version 2.5                 April 1995                    FLEX(1)