A C Program a Day

2019-10-02 - dd progress display

I often run dd to copy a disk image onto a USB key. But by default, dd doesn't show its progress as it runs, and it can sometimes take a while. So here's a small program which is like cat, but it prints how much data it has outputted to stderr. You can use it with dd like this:

dd if=something.iso | ./2019_10_02 | dd of=/dev/sdb
Today's procedure is writed, which outputs a floating-point number.


#include "procs-2019-10-02.c"

int main(void) {
	static char buffer[1L<<20];
	long total = 0;
	ssize_t bytesread;
	while ((bytesread = read(STDIN, buffer, sizeof buffer)) > 0) {
		total += (long)bytesread;
		write(STDERR, "\r", 1);
		if (total >= (1L<<30)) {
			writed(STDERR, (double)total / (double)(1L<<30), 1);
			write(STDERR, "GB", 2);
		} else if (total >= (1L<<20) * 10) {
			writel(STDERR, total / (1L<<20));
			write(STDERR, "MB", 2);
		} else if (total >= (1L<<20)) {
			writed(STDERR, (double)total / (double)(1L<<20), 1);
			write(STDERR, "MB", 2);
		} else if (total >= (1L<<10) * 10) {
			writel(STDERR, total / (1L<<10));
			write(STDERR, "KB", 2);
		} else if (total >= (1L << 10)) {
			writed(STDERR, (double)total / (double)(1L<<10), 1);
			write(STDERR, "KB", 2);
		} else {
			writel(STDERR, total);
			write(STDERR, "B", 1);
		write(STDERR, "    \r", 5);
		write(STDOUT, buffer, (size_t)bytesread);
	write(STDERR, "\n", 1);
	if (bytesread < 0) {
		char err[] = "write error";
		write(STDERR, err, sizeof err - 1);
		return EXIT_FAILURE;
	return 0;

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