coreutils

// echo.c, version 1.1.0

// OMKOV coreutils implementation of POSIX echo

// Copyright (C) 2020, Jakob Wakeling

// MIT Licence

#include <stdio.h>

#include <stdlib.h>

static inline void echo(const char *s);

int main(int ac, char *av[]) { (void)ac;

	register char **p = &av[1]; if (*p) { echo(*p);

		for (++p; *p; ++p) { fputc(' ', stdout); echo(*p); }

	} fputc('\n', stdout); return 0;

}

/*

	Echo a string to stdout character by character.

	Escape sequences are processed according to XSI.

*/

static inline void echo(const char *s) {

	for (const char *p = s; *p; ++p) {

		if (*p == '\\' && p[1]) switch (*++p) {

		case 'a': { fputc('\a', stdout); continue; }

		case 'b': { fputc('\b', stdout); continue; }

		case 'c': { exit(0); }

		case 'f': { fputc('\f', stdout); continue; }

		case 'n': { fputc('\n', stdout); continue; }

		case 'r': { fputc('\r', stdout); continue; }

		case 't': { fputc('\t', stdout); continue; }

		case 'v': { fputc('\v', stdout); continue; }

		case '\\': { fputc('\\', stdout); continue; }

		case '0': {

			register int n = 0, d = 0;

			for (++p; (*p >= '0' && *p <= '7') && d++ != 3; ++p) {

				n <<= 3; n |= (*p - '0');

			} fputc(n, stdout); --p; continue;

		}

		default: { fputc('\\', stdout); fputc(*p, stdout); }

		} else { fputc(*p, stdout); continue; }

	} return;

}