Add support for yorn(), safe yes-or-no prompt

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

src/yorn.c

@@ -0,0 +1,92 @@
+/* Safe yes-or-no with prompt
+ *
+ * Copyright (c) 2009  Joachim Nilsson <troglobit@gmail.com>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <stdio.h>
+#include <stdio_ext.h>		/* __fpurge() */
+#include <stdarg.h>
+#include <termios.h>
+#include <unistd.h>
+
+static char rawgetch(void)
+{
+	struct termios savemodes, modmodes;
+	char val;
+
+	if (!isatty(STDIN_FILENO))
+		return getchar();
+
+	/* Backup terminal settings. */
+	if (tcgetattr(STDIN_FILENO, &savemodes) < 0) {
+		return -1;
+	}
+
+	/* "stty cbreak -echo" */
+	modmodes = savemodes;
+	modmodes.c_lflag &= ~ICANON;
+	modmodes.c_lflag &= ~ECHO;
+	modmodes.c_cc[VMIN] = 1;
+	modmodes.c_cc[VTIME] = 0;
+
+	/* Set terminal in raw mode. */
+	if (tcsetattr(STDIN_FILENO, TCSANOW, &modmodes) < 0) {
+		tcsetattr(STDIN_FILENO, TCSANOW, &savemodes);
+		return -1;
+	}
+
+	val = getchar();
+
+	/* Restore terminal to previous state. */
+	tcsetattr(STDIN_FILENO, TCSANOW, &savemodes);
+
+	return val;
+}
+
+/**
+ * yorn - Pose a a Yes or No question and return answer
+ * @fmt: Standard printf() style argument(s).
+ *
+ * This function prints the given question on screen, waits for user
+ * input in the form of yes or no.
+ *
+ * Returns:
+ * True(1) or False(0).  True if the answer is yes.
+ */
+int yorn(const char *fmt, ...)
+{
+	va_list ap;
+	char yorn;
+
+	va_start(ap, fmt);
+	vfprintf(stderr, fmt, ap);
+	va_end(ap);
+
+	__fpurge(stdin);
+	yorn = rawgetch();
+	printf("%c\n", yorn);
+	fflush(stdout);
+	if (yorn != 'y' && yorn != 'Y')
+		return 0;
+
+	return 1;
+}
+
+/**
+ * Local Variables:
+ *  indent-tabs-mode: t
+ *  c-file-style: "linux"
+ * End:
+ */