Lex (software) - Example of A Lex File

Example of A Lex File

The following is an example Lex file for the flex version of Lex. It recognizes strings of numbers (integers) in the input, and simply prints them out.

/*** Definition section ***/ %{ /* C code to be copied verbatim */ #include %} /* This tells flex to read only one input file */ %option noyywrap %% /*** Rules section ***/ /* + matches a string of one or more digits */ + { /* yytext is a string containing the matched text. */ printf("Saw an integer: %s\n", yytext); } .|\n { /* Ignore all other characters. */ } %% /*** C Code section ***/ int main(void) { /* Call the lexer, then quit. */ yylex; return 0; }

If this input is given to flex, it will be converted into a C file, lex.yy.c. This can be compiled into an executable which matches and outputs strings of integers. For example, given the input:

abc123z.!&*2gj6

the program will print:

Saw an integer: 123 Saw an integer: 2 Saw an integer: 6

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