

FLEX(1)                   Minix Programmer's Manual                    FLEX(1)


NAME
     flex, lex - fast lexical analyzer generator

SYNOPSIS
     flex [-bcdfinpstvFILT8 -C[efmF] -Sskeleton] [filename ...]

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
     expressions.  Whenever it finds one,  it  executes  the  corresponding  C
     code.

     For full documentation, see flexdoc(1). This manual entry is intended for
     use as a quick reference.

OPTIONS
     flex has the following options:

     -b   Generate backtracking information to lex.backtrack. This is  a  list
          of   scanner   states  which  require  backtracking  and  the  input
          characters on which they do so.  By  adding  rules  one  can  remove
          backtracking  states.  If all backtracking states are eliminated and
          -f or -F is used, the generated scanner will run faster.

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

          NOTE: in previous releases of flex  -c  specified  table-compression
          options.   This  functionality is now given by the -C flag.  To ease
          the the impact of this change, when flex encounters -c, it currently
          issues  a  warning  message and assumes that -C was desired instead.
          In the future this "promotion" of -c to -C will go away in the  name
          of  full  POSIX  compliance  (unless  the  POSIX  meaning is removed
          first).

     -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 backtracks, accepts the
          default  rule,  reaches the end of its input buffer (or encounters a
          NUL; the two look the same as far as the  scanner's  concerned),  or
          reaches an end-of-file.

     -f   specifies (take your pick) full table  or  fast  scanner.  No  table
          compression  is done.  The result is large but fast.  This option is
          equivalent to -Cf (see below).


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     -i   instructs flex to generate a case-insensitive scanner.  The case  of
          letters given in the flex input patterns will be ignored, and tokens
          in the input will be matched regardless of case.  The  matched  text
          given  in  yytext will have the preserved case (i.e., it will not be
          folded).

     -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 loss of performance in the resulting scanner.

     -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.

     -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 summary  of  statistics
          regarding the scanner it generates.

     -F   specifies that the fast scanner table representation should be used.
          This   representation   is   about   as   fast  as  the  full  table
          representation  (-f),  and  for  some  sets  of  patterns  will   be
          considerably  smaller  (and for others, larger).  See flexdoc(1) for
          details.

          This option is equivalent to -CF (see below).

     -I   instructs flex to  generate  an  interactive  scanner,  that  is,  a
          scanner  which  stops  immediately  rather  than looking ahead if it
          knows that the currently scanned text cannot be  part  of  a  longer
          rule's match.  Again, see flexdoc(1) for details.

          Note, -I cannot be used in conjunction with  full  or  fast  tables,
          i.e., the -f, -F, -Cf, or -CF flags.

     -L   instructs flex not to generate #line  directives  in  lex.yy.c.  The
          default  is  to  generate  such  directives so error messages in the
          actions will be correctly located with respect to the original  flex
          input  file,  and  not  to  the  fairly  meaningless line numbers of
          lex.yy.c.

     -T   makes flex run in trace mode.  It will generate a lot of messages to
          stdout  concerning  the  form  of  the  input and the resultant non-
          deterministic and deterministic finite  automata.   This  option  is
          mostly for use in maintaining flex.

     -8   instructs flex to generate an 8-bit scanner.  On some sites, this is
          the  default.   On  others, the default is 7-bit characters.  To see
          which is the case, check the verbose (-v)  output  for  "equivalence
          classes  created".   If  the denominator of the number shown is 128,
          then by default flex is generating 7-bit characters.  If it is  256,
          then the default is 8-bit characters.


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     -C[efmF]
          controls the degree of table compression.

          -Ce directs flex to construct equivalence  classes,  i.e.,  sets  of
          characters  which  have  identical  lexical properties.  Equivalence
          classes usually give dramatic reductions in the  final  table/object
          file  sizes  (typically  a  factor  of  2-5)  and  are  pretty cheap
          performance-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 functions for different states.

          -CF  specifies  that  the  alternate  fast  scanner   representation
          (described in flexdoc(1)) should be used.

          -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-
          equivalence  classes  are  often  a  big  win  when using compressed
          tables, but they have a moderate performance impact (one or two "if"
          tests and one array look-up per character scanned).

          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-equivalence  classes  if the table is not
          being compressed.  Otherwise the options may be freely mixed.

          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  off  faster-executing  scanners  at the cost of larger tables
          with the following generally being true:

              slowest & smallest
                    -Cem
                    -Cm
                    -Ce
                    -C
                    -C{f,F}e
                    -C{f,F}
              fastest & largest


          -C options are not cumulative; whenever the flag is encountered, the
          previous -C settings are forgotten.

     -Sskeleton_file
          overrides the default skeleton file from which flex  constructs  its
          scanners.   You'll  never need this option unless you are doing flex
          maintenance or development.




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FLEX(1)                   Minix Programmer's Manual                    FLEX(1)


SUMMARY OF FLEX REGULAR EXPRESSIONS
     The patterns in the input are written using an extended  set  of  regular
     expressions.  These are:

         x          match the character 'x'
         .          any character 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 '*')
         \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
                      regular expression s; called "concatenation"


         r|s        either an r or an s


         r/s        an r but only if it is followed by an s.  The
                      s is not part of the matched text.  This type
                      of pattern is called as "trailing context".
         ^r         an r, but only at the beginning of a line
         r$         an r, but only at the end of a line.  Equivalent
                      to "r/\n".


         <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


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

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

     Some notes on patterns:

     -    Negated  character  classes  match  newlines  unless  "\n"  (or   an
          equivalent  escape  sequence)  is  one  of the characters explicitly
          present in the negated character class (e.g., "[^A-Z\n]").

     -    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.  The following are all illegal:

              foo/bar$
              foo|(bar$)
              foo|^bar
              <sc1>foo<sc2>bar


SUMMARY OF SPECIAL ACTIONS
     In addition to arbitrary C code, the following can appear in actions:

     -    ECHO copies yytext to the scanner's output.

     -    BEGIN followed by the name of a start condition places  the  scanner
          in the corresponding start condition.

     -    REJECT directs the scanner to proceed on to the "second  best"  rule
          which  matched  the  input  (or  a prefix of the input).  yytext and
          yyleng are set up appropriately.  Note that REJECT is a particularly
          expensive feature in terms scanner performance; if it is used in any
          of the scanner's actions it will slow  down  all  of  the  scanner's
          matching.   Furthermore,  REJECT  cannot  be  used with the -f or -F
          options.

          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 than replacing it.

     -    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 ).





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FLEX(1)                   Minix Programmer's Manual                    FLEX(1)


     -    unput(c) puts the character c back onto the input stream.   It  will
          be the next character scanned.

     -    input() reads the next character from the input stream (this routine
          is called yyinput() if the scanner is compiled using C++).

     -    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.

     -    YY_NEW_FILE is an action available only in <<EOF>> rules.  It  means
          "Okay, I've set up a new input file, continue scanning".

     -    yy_create_buffer( file, size ) takes a FILE pointer and  an  integer
          size.  It  returns  a  YY_BUFFER_STATE  handle to a new input buffer
          large enough to accomodate size characters and associated  with  the
          given file.  When in doubt, use YY_BUF_SIZE for the size.

     -    yy_switch_to_buffer( new_buffer ) switches the scanner's  processing
          to  scan  for  tokens  from  the  given  buffer,  which  must  be  a
          YY_BUFFER_STATE.

     -    yy_delete_buffer( buffer ) deletes the given buffer.

VALUES AVAILABLE TO THE USER

     -    char *yytext holds the text of the current token.   It  may  not  be
          modified.

     -    int yyleng holds the length of the current token.   It  may  not  be
          modified.

     -    FILE *yyin is the file which by default flex reads from.  It may  be
          redefined  but  doing  so  only  makes sense before scanning begins.
          Changing it in the middle of scanning will have  unexpected  results
          since  flex  buffers its input.  Once scanning terminates because an
          end-of-file has been seen, void yyrestart( FILE *new_file )  may  be
          called to point yyin at the new input file.

     -    FILE *yyout is the file to which ECHO actions are done.  It  can  be
          reassigned by the user.

     -    YY_CURRENT_BUFFER returns a YY_BUFFER_STATE handle  to  the  current
          buffer.

MACROS THE USER CAN REDEFINE

     -    YY_DECL controls how the scanning routine is declared.  By  default,
          it  is  "int  yylex()",  or,  if  prototypes  are  being  used, "int
          yylex(void)".  This definition may  be  changed  by  redefining  the
          "YY_DECL"  macro.   Note  that if you give arguments to the scanning
          routine using a K&R-style/non-prototyped function  declaration,  you
          must terminate the definition with a semi-colon (;).


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     -    The nature of how the scanner gets its input can  be  controlled  by
          redefining  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 systems) to indicate EOF.  The default
          YY_INPUT reads  from  the  global  file-pointer  "yyin".   A  sample
          redefinition  of  YY_INPUT  (in the definitions section of the input
          file):

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


     -    When the scanner receives an end-of-file indication  from  YY_INPUT,
          it  then  checks  the  yywrap() function.  If yywrap() returns false
          (zero), then it is assumed that the function has gone ahead and  set
          up  yyin to point to another input file, and scanning continues.  If
          it returns true (non-zero), then the scanner terminates, returning 0
          to its caller.

          The default yywrap() always returns 1.  Presently,  to  redefine  it
          you  must first "#undef yywrap", as it is currently implemented as a
          macro.  It is likely that yywrap() will soon  be  defined  to  be  a
          function rather than a macro.

     -    YY_USER_ACTION can be redefined to provide an action which is always
          executed prior to the matched rule's action.

     -    The macro YY_USER_INIT may be redefined to provide an  action  which
          is always executed before the first scan.

     -    In the generated scanner, the actions are all gathered in one  large
          switch   statement  and  separated  using  YY_BREAK,  which  may  be
          redefined.  By default, it is simply a  "break",  to  separate  each
          rule's action from the following rule's.

FILES

     flex.skel
          skeleton scanner.

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

     lex.backtrack
          backtracking  information  for  -b  flag  (called  lex.bck  on  some
          systems).




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FLEX(1)                   Minix Programmer's Manual                    FLEX(1)


     -lfl library with which to link the scanners.

SEE ALSO

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

     M. E. Lesk and E. Schmidt, LEX - Lexical Analyzer Generator

DIAGNOSTICS
     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).
     Make  an explicit reference to the action in your flex input file.  (Note
     that previously flex supported a %used/%unused mechanism for dealing with
     this  problem;  this  feature  is still supported but now deprecated, and
     will go away soon unless the author  hears  from  people  who  can  argue
     compellingly that they need it.)

     flex scanner jammed - a scanner compiled with -s has encountered an input
     string which wasn't matched by any of its rules.

     flex input buffer overflowed - a  scanner  rule  matched  a  string  long
     enough  to  overflow  the  scanner's  internal  input buffer (16K bytes -
     controlled by YY_BUF_MAX in "flex.skel").

     scanner  requires  -8  flag  -  Your   scanner   specification   includes
     recognizing  8-bit  characters  and  you did not specify the -8 flag (and
     your site has not installed flex with -8 as the default).

     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 activation frame.   Before  reentering  the  scanner,
     use:

         yyrestart( yyin );


     too many %t classes! - You managed to put every single character into its
     own  %t  class.   flex  requires  that  at least one of the classes share
     characters.

AUTHOR
     Vern Paxson, with the help of many ideas and much  inspiration  from  Van
     Jacobson.  Original version by Jef Poskanzer.

     See flexdoc(1) for additional credits and the address  to  send  comments
     to.







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FLEX(1)                   Minix Programmer's Manual                    FLEX(1)


DEFICIENCIES / BUGS

     Some trailing context patterns cannot be properly  matched  and  generate
     warning  messages  ("Dangerous  trailing  context").   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 abovementioned performance
     loss.  In particular, parts using '|'  or  {n}  (such  as  "foo{3}")  are
     always considered variable-length.

     Combining trailing context with the special  '|'  action  can  result  in
     fixed  trailing  context  being  turned  into the more expensive variable
     trailing context.  For example, this happens in the following example:

         %%
         abc      |
         xyz/def


     Use of unput() invalidates yytext and yyleng.

     Use of unput() to push back more text than was matched can result in  the
     pushed-back  text  matching a beginning-of-line ('^') rule even though it
     didn't come at the beginning of the line (though this is rare!).

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

     flex does not generate correct #line directives for code internal to  the
     scanner; thus, bugs in flex.skel yield bogus line numbers.

     Due to both buffering of input and read-ahead, you cannot intermix  calls
     to  <stdio.h>  routines, such as, for example, 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 number 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.

     Some of the macros, such as yywrap(), may in the future become  functions
     which live in the -lfl library.  This will doubtless break a lot of code,
     but may be required for POSIX-compliance.

     The flex internal algorithms need documentation.







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