Simple program to take an input from the stdin and spit it to stdout on a single line without any duplicate whitespace. Not as efficient as it could be, but quick and dirty.

onelineit.c

#include <stdio.h>


main(){
	int c;
	while((c = getchar()) != EOF){
		if(c == '\n'){
			putchar(' ');
			while((c = getchar()) == '\n')
				;
			if(c != ' ' && c != '\t')
				putchar(c);
			continue;
		}
		if(c == '\t'){
			putchar(' ');
			while((c = getchar()) == '\t')
				;
			if(c != ' ' && c != '\n')
				putchar(c);
			continue;	
		}
		putchar(c);
		if(c == ' '){
			while((c = getchar()) == ' ')
				;
			putchar(c);
		}
	}
	//Move curser down
	printf("\n");
	//Use ctrl+D on unix systems to output an EOF to stdin
}

To run it:

$cc onelineit.c -o onelineit
$./onelineit < inputfile.txt > output.txt