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lex(1)									lex(1)

NAME    [Toc]    [Back]

     lex - generate programs for simple	lexical	tasks

SYNOPSIS    [Toc]    [Back]

     lex [-ctvn	-V -Q[y|n]] [file<b>]

DESCRIPTION    [Toc]    [Back]

     NOTE: When	the environment	variable _XPG is a value greater than 0
     (zero), lex execs the POSIX compliant /usr/bin/flex.

     The lex command 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 these
     strings are found.	 lex processes supplementary code set characters in
     program comments and strings, and single-byte supplementary code set
     characters	in tokens, according to	the locale specified in	the LC_CTYPE
     environment variable [see LANG on environ(5)].

     lex generates a file named	lex.yy.c.  When	lex.yy.c is compiled and
     linked with the lex library (/usr/lib/libl.a), it copies the input	to the
     output except when	a string specified in the file is found.  When a
     specified string 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	patterns in the	file.
     The patterns 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	non-negative 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 characters except	new-line.  Parentheses
     for grouping and vertical bar for alternation are also supported.	The
     notation r<b>{d<b>,e<b>} 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 new-line, and the
     character $ at the	end of an expression requires a	trailing new-line.
     The character / in	an expression indicates	trailing context; only the
     part of the expression up to the slash is returned	in yytext, but the
     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 macros are expected:	 input to read a character; unput(c<b>) to
     replace a character read; and output(c<b>) 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 lex library contains
     a main that calls it.  The	macros input and output	read from and write to
     stdin and stdout, respectively.

     The function yymore accumulates additional	characters into	the same
     yytext.  The function yyless(n<b>) pushes back yyleng	-n characters into the
     input stream.  (yyleng is an external long	int variable giving the	length

									Page 1

lex(1)									lex(1)

     in	bytes of yytext.)  The function	yywrap is called whenever the scanner
     reaches end of file and indicates whether normal wrapup should continue.
     The action	REJECT on the right side of the	rule causes the	match to be
     rejected and the next suitable match executed.  The action	ECHO on	the
     right side	of the rule is equivalent to printf("%s", yytext).

     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 %% that begin with a non-blank character	define the string on
     the left to be the	remainder of the line; it can be called	out later by
     surrounding it with {}.  In this section, C code (and preprocessor
     statements) can also be included between %{ and %}.  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.

     The flags must appear before any files.

     -c	      Indicates	C actions and is the default.

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

     -v	      Provides a two-line summary of statistics.

     -n	      Will not print out the -v	summary.

     -V	      Print out	version	information on standard	error.

     -Q[y|n]  Print out	version	information to output file lex.yy.c by using
	      -Qy.  The	-Qn option does	not print out version information and
	      is the default.

     Multiple files are	treated	as a single file.  If no files are specified,
     standard input is used.

     Certain default table sizes are too small for some	users.	The table
     sizes for the resulting finite state machine can be set in	the
     definitions section:

	  %p n number of positions is n	(default 20000)

	  %n n number of states	is n (4000)

	  %e n number of parse tree nodes is n (8000)

	  %a n number of transitions is	n (16000)

	  %k n number of packed	character classes is n (20000)

									Page 2

lex(1)									lex(1)

	  %o n size of output array is n (24000)

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

EXAMPLE    [Toc]    [Back]

	     D	     [0-9]

	     if	     printf("IF	statement\n");
	     [a-z]+  printf("tag, value	%s\n",yytext);
	     0{D}+   printf("octal number %s\n",yytext);
	     {D}+    printf("decimal number %s\n",yytext);
	     "++"    printf("unary op\n");
	     "+"     printf("binary op\n");
	     "\n"    ;/*no action */
	     "/*"      skipcommnts();

SEE ALSO    [Toc]    [Back]


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