How do I input to lexer via stdin?

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Flex

Greetings Kind Regards I am learning to utilize flex and bison but for now my question is re/ flex i.e. to wit in particular how to input a string via stdin to be recognized by the generated lexer. The flex input file is below and lexer generated via
win_flex --wincompat --noyywrap flex.y
The token rule is merely that for the C language identifier.
flex.y

%%
\b[_a-zA-Z][_a-zA-Z0-9]*\b		printf("hello, world\n");
%%
 main()
        {
        yylex();
        }

Upon compilation and execution of generated file I merely type in e.g. "abc" w/o quotes then <enter> and expect "hello, world\n" to be printed as it is the action associated w/ the rule, however it is not, only ECHO is called in the switch statement below i.e. case 2:

		switch ( yy_act )
	{ /* beginning of action switch */
			case 0: /* must back up */
			/* undo the effects of YY_DO_BEFORE_ACTION */
			*yy_cp = (yy_hold_char);
			yy_cp = (yy_last_accepting_cpos);
			yy_current_state = (yy_last_accepting_state);
			goto yy_find_action;

case 1:
YY_RULE_SETUP
//#line 2 "flex.y"
printf("hello, world\n");
	YY_BREAK
case 2:
YY_RULE_SETUP
//#line 3 "flex.y"
ECHO;
	YY_BREAK
//#line 730 "lex.yy.c"
case YY_STATE_EOF(INITIAL):
	yyterminate();

	case YY_END_OF_BUFFER:
		{
		/* Amount of text matched not including the EOB char. */
		int yy_amount_of_matched_text = (int) (yy_cp - (yytext_ptr)) - 1;
...}

So I do not know if I am specigying input file incorrectly, generating incorrectly or entering via stdin incorrectly. Kindly Advise - Thank You

What I have tried:

Every conceivable string termination via keyboard i.e. to wit in particular <enter>, <ctrl>+c, <ctrl>+z, space character, and the usual internet search