C-Code

/********************************************
 * fred_3.c   search pattern in input stream
 *            using child process
 * 
 * OS     :   GNU/Linux
 * compile:   gcc -Wall -o fred fred_3.c
 * example:   echo Freddy|./fred -i fred    				
 *
 * devnull    28-06-2013                
 ********************************************/
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#define STR_LEN   62
#define BUF_LEN  254


/************
 * functions
 ************/
/* print usage on stderr */
void usage_exit( int exit_code )
{
  fprintf( stderr, "Usage: fred [-i] pattern\n" );
  exit(exit_code);
}

/* read input line from stdin */
int readln( char *line, int stripLF )
{
	int len;
	
	if (fgets(line, BUF_LEN, stdin) != NULL) {
		line[BUF_LEN]='\0';
		len=strlen(line);
		if (stripLF) {
			if (line[len-1] == '\n') {
				line[len-1] = '\0';
				len--;
			}
		}
		return len;
	}
	else
		return -1;
}

/*********
 *  main
 *********/
int main( int argc, char **argv )
{
    char linebuf[BUF_LEN+1];
    char pattern[STR_LEN+1];
    char command[STR_LEN+1];
    int opt, opt_icase=0;
    int slen;
    FILE* pp;

    /* check options [ih] */
    while ((opt = getopt( argc, argv, "ih" )) != -1) {
      switch(opt) {
          case 'i': opt_icase=1;         break;
          case 'h': usage_exit(EXIT_SUCCESS); break;
          default : usage_exit(EXIT_FAILURE);
      }
    }

	/* check args: search string/pattern */
    if (argc-optind != 1) 
		usage_exit(EXIT_FAILURE);
    strncpy( pattern,  argv[optind], STR_LEN );
    pattern[STR_LEN] = '\0';
	slen=strlen(pattern);
	if (slen == 0) {
		fprintf( stderr, "empty search string\n" );
		return 2;
	}

	/* build 'grep' command line */
	snprintf( command,STR_LEN,"/bin/grep -n%s '%s' -",opt_icase?"i":"",pattern );

	/* open pipe stream to child process */
	if ((pp=popen( command, "w" )) != NULL) {
		while (readln(linebuf,0) >= 0)
			fputs(linebuf,pp);
		pclose(pp);
	}
	else {
		fprintf( stderr, "cannot open pipe stream\n" );
		return 3;
	}
	return 0;
}