Moreutils: Added ifne

Hi, I read the suggestion about ifne in the Discussion page of
moreutils and found it interesting. It's a command that runs another
process if the standard input is not empty. I think it can be very
useful in admin scripts so I've implemented it. I attach a patch
against the current head of moreutils' git. You may include it in
moreutils if you think it's worth it.

I've considered making an "ifempty" or "ifne -v" that would run a
command if the standard input is empty, but I'm not sure if that could
be useful. Any comments will be appreciated. Regards,

Javi

1 files changed, 99 insertions, 0 deletions

diff --git a/ifne.c b/ifne.c
new file mode 100644
index 0000000..9af19fa
--- /dev/null
+++ b/ifne.c
@@ -0,0 +1,99 @@
+
+/* 
+ *
+ * Copyright 2008 Javier Merino <cibervicho@gmail.com>
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+ * Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ *
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/wait.h>
+#include <sys/types.h>
+
+int main(int argc, char **argv) {
+	ssize_t r;
+	int fds[2];
+	int child_status;
+	pid_t child_pid;
+	char buf[BUFSIZ];
+
+	if (argc < 2) {
+		/* Noop */
+		return EXIT_SUCCESS;
+	}
+
+	r = read(0, buf, BUFSIZ*sizeof(char));
+
+	if (r == 0)
+		return EXIT_SUCCESS;
+	else if (r == -1) {
+		perror("read");
+		return EXIT_FAILURE;
+	}
+
+	if (pipe(fds)) {
+		perror("pipe");
+		return EXIT_FAILURE;
+	}
+
+	child_pid = fork();
+	if (!child_pid) {
+		/* child process: rebind stdin and exec the subcommand */
+		close(fds[1]);
+		if (dup2(fds[0], 0)) {
+			perror("dup2");
+			return EXIT_FAILURE;
+                }
+
+		execvp(argv[1], &argv[1]);
+		perror(argv[1]);
+		close(fds[0]);
+		return EXIT_FAILURE;
+	} else if (child_pid == -1) {
+		perror("fork");
+		return EXIT_FAILURE;
+	}
+
+	/* Parent: write in fds[1] our stdin */
+	close(fds[0]);
+
+	do {
+		if (write(fds[1], buf, r*sizeof(char)) == -1) {
+			fprintf(stderr, "Write error to %s\n", argv[1]);
+			exit(EXIT_FAILURE);
+		}
+		r = read(0, buf, BUFSIZ*sizeof(char));
+	} while (r > 0);
+	if (r == -1) {
+		perror("read");
+		exit(EXIT_FAILURE);
+	}
+	
+	close(fds[1]);
+	if (waitpid(child_pid, &child_status, 0) != child_pid) {
+		perror("waitpid");
+		return EXIT_FAILURE;
+	}
+	if (WIFEXITED(child_status)) {
+		return (WEXITSTATUS(child_status));
+	} else if (WIFSIGNALED(child_status)) {
+		raise(WTERMSIG(child_status));
+		return EXIT_FAILURE;
+	}
+
+	return EXIT_FAILURE;
+}