lex(1)                                                     lex(1)



NAME
     lex - generates programs for simple lexical tasks

SYNOPSIS
     lex [-c] [-n] [-t] [-v] [file]...

ARGUMENTS
     -c   Indicates C actions and is the default.

     file Specifies the input file to be used by lex.  Multiple
          files are treated as a single file.  If no files are
          specified, standard input is used.

     -n   Does not print out the summary.

     -t   Causes the lex.yy.c program to be written instead to
          standard output.

     -v   Provides a one-line summary of statistics of the
          machine generated.

DESCRIPTION
     lex generates programs to be used in simple lexical analysis
     of text.

     The input files (standard input default) contain strings and
     expressions to be searched for, and C text to be executed
     when strings are found.

     A file lex.yy.c is generated which, when loaded with the
     library, copies the input to the output except when a string
     specified in the file is found; then the corresponding
     program text is executed.  The actual string matched is left
     in yytext, an external character array.  Matching is done in
     order of the strings in the file.  The strings may contain
     square brackets to indicate character classes, as in [abx-z]
     to indicate a, b, x, y, and z; and the operators *, +, and ?
     mean, respectively, any nonnegative number of, any positive
     number of, and either zero or one occurrence of, the
     previous character or character class.  Thus [a-zA-Z]+
     matches a string of letters.  The character . is the class
     of all ASCII characters except newline.  Parentheses for
     grouping and vertical bar for alternation are also
     supported.  The notation r{d,e} in a rule indicates between
     d and e instances of regular expression r.  It has higher
     precedence than |, but lower than *, ?, +, and
     concatenation.  The character ^ at the beginning of an
     expression permits a successful match only immediately after
     a newline, and the character $ at the end of an expression
     requires a trailing newline.  The character / in an
     expression indicates trailing context; only the part of the
     expression up to the slash is returned in yytext, but the



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lex(1)                                                     lex(1)



     remainder of the expression must follow in the input stream.
     An operator character may be used as an ordinary symbol if
     it is within " symbols or preceded by \ .

     Three subroutines defined as macros are expected:  input()
     to read a character; unput(c) to replace a character read;
     and output(c) to place an output character.  They are
     defined in terms of the standard streams, but you can
     override them.  The program generated is named yylex(), and
     the library contains a main() which calls it.  The action
     REJECT on the right side of the rule causes this match to be
     rejected and the next suitable match executed; the function
     yymore() accumulates additional characters into the same
     yytext; and the function yyless(p) pushes back the portion
     of the string matched beginning at p, which should be
     between yytext and yytext+yyleng.  The macros input and
     output use files yyin and yyout to read from and write to,
     defaulted to stdin and stdout, respectively.

     Any line beginning with a blank is assumed to contain only C
     text and is copied; if it precedes %%, it is copied into the
     external definition area of the lex.yy.c file.  All rules
     should follow a %%, as in YACC.  Lines preceding %% which
     begin with a nonblank character define the string on the
     left to be the remainder of the line; it can be called out
     later by surrounding it with {}.  Note that curly brackets
     do not imply parentheses; only string substitution is done.

     The external names generated by lex all begin with the
     prefix yy or YY.

     Certain table sizes for the resulting finite state machine
     can be set in the definitions section:

          %p n number of positions is n (default 2000)

          %n n number of states is n (500)

          %t n number of parse tree nodes is n (1000)

          %a n number of transitions is n (3000)

     The use of one or more of the above automatically implies
     the -v option, unless the -n option is used.

EXAMPLES
     The following is output that was generated by lex:

        D       [0-9]
        %%
        if      printf("IF statement\n");
        [a-z]+ printf("tag, value %s\n",yytext);



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lex(1)                                                     lex(1)



        0{D}+   printf("octal number %s\n",yytext);
        {D}+    printf("decimal number %s\n",yytext);
        "++"    printf("unary op\n");
        "+"     printf("binary op\n");
        "/*"    {    loop:
                while (input() != '*');
                     switch (input())
                                {
                                case '/': break;
                                case '*': unput('*');
                                default: go to loop;
                                }
                        }


LIMITATIONS
     When given an illegal option, lex reports the fact that it
     has been given an illegal option but then continues to
     execute with the default options, rather than stopping the
     execution and printing a usage statement.

FILES
     /usr/bin/lex
          Executable file

SEE ALSO
     awk(1), grep(1), sed(1), yacc(1)

     malloc(3X) in A/UX Programmer's Reference

     ``lex Reference'' in A/UX Programming Languages and Tools,
     Volume 2























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