1 files changed, 105 insertions, 0 deletions
diff --git a/src/echo.c b/src/echo.c
new file mode 100644
index 0000000..fbf74bd
--- /dev/null
+++ b/src/echo.c
@@ -0,0 +1,105 @@
+#define _POSIX_C_SOURCE 2
+#include <unistd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+#include <ctype.h>
+#include <stdint.h>
+
+bool isodigit(char c)
+{
+	return c >= '0' && c < '8';
+}
+
+int main(int argc, char **argv)
+{
+	int  option;
+	bool escape  = false;
+	bool newline = true;
+
+	while ((option = getopt(argc, argv, "neE")) != -1)
+	{
+		switch (option)
+		{
+			case 'e': escape  = true;  break;
+			case 'E': escape  = false; break;
+			case 'n': newline = false; break;
+		}
+	}
+	for (; optind < argc; optind++)
+	{
+		char *str = argv[optind];
+		if (escape)
+		{
+			for (size_t i = 0; str[i] != '\0'; i++)
+			{
+				if (str[i] == '\\')
+				{
+					uint8_t c     = 0;
+					int     shift = 1;
+
+					switch (str[i + 1])
+					{
+						case '\\': c = '\\'; break;
+						case 'a': c = '\a'; break;
+						case 'b': c = '\b'; break;
+						case 'e': c = '\033'; break;
+						case 'f': c = '\f'; break;
+						case 'n': c = '\n'; break;
+						case 'r': c = '\r'; break;
+						case 't': c = '\t'; break;
+						case 'v': c = '\v'; break;
+
+						case '0':
+							c = 0;
+							for (int j = 0; isodigit(str[i + 2 + j]) && j < 3; j++)
+							{
+								c *= 8;
+								c += str[i + 2 + j] - '0';
+								shift++;
+							}
+							break;
+
+						case 'x':
+							c = 0;
+							for (int j = 0; isxdigit(str[i + 2 + j]) && j < 2; j++)
+							{
+								c *= 16;
+								if (islower(str[i + 2 + j]))
+									c += 10 + str[i + 2 + j] - 'a';
+								else if (isupper(str[i + 2 + j]))
+									c += 10 + str[i + 2 + j] - 'A';
+								else
+									c += str[i + 2 + j] - '0';
+								shift++;
+							}
+							break;
+
+						case 'c':
+							str[i] = '\0';
+							fputs(str, stdout);
+							fflush(stdout);
+							exit(EXIT_SUCCESS);
+							break;
+
+						default:
+							shift = -1;
+							break;
+					}
+					if (shift != -1)
+					{
+						str[i] = c;
+						memmove(&str[i + 1], &str[i + 1 + shift], strlen(&str[i + 1 + shift]) + 1);
+					}
+				}
+			}
+		}
+		fputs(str, stdout);
+		if (optind + 1 != argc)
+			putchar(' ');
+	}
+	if (newline)
+		putchar('\n');
+	return EXIT_SUCCESS;
+}