* Add mispipe, contributed by Nathanael Nerode. Pipes together two commands,

  returning the exit status of the first.

1 files changed, 179 insertions, 0 deletions

diff --git a/mispipe.c b/mispipe.c
new file mode 100644
index 0000000..43ba76a
--- /dev/null
+++ b/mispipe.c
@@ -0,0 +1,179 @@
+/*
+ * mispipe: written by Nathanael Nerode.
+ *
+ * Copyright 2004 Nathanael Nerode.
+ *
+ * Licensed under the GPL version 2 or above, and dual-licensed under the
+ * following license:
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN 
+ * THE SOFTWARE.
+ */
+
+/*
+ * Usage: mispipe <command1> <command2>
+ * Run <command1> | <command2>, but return with the exit status of <command1>.
+ *
+ * This is designed for a very specific purpose: logging.
+ * "foo | logger -t foo"
+ * will return with the exit status of logger, not that of foo.
+ * "mispipe foo 'logger -t foo'"
+ * will return with the exit status of foo.
+ */
+
+/*
+ * To do:
+ * Make this into a fancy, internationalized, option-handling hellbeast.
+ * (But why bother?  It does its job quite well.)
+ */
+
+#include <errno.h> /* errno */
+#include <sys/types.h>
+#include <unistd.h> /* pipe(), fork(),... */
+#include <stdlib.h> /* system() */
+#include <sys/wait.h> /* waitpid(), etc. */
+#include <stdio.h>
+#include <stdarg.h> /* va_list, for error() */
+
+static const char* progname; /* Stores argv[0] */
+static int filedes[2]; /* Stores pipe file descriptors */
+
+/* Subroutine for 'warning' and 'error' which prefixes progname */
+static void warning_prefix(void) {
+	fputs(progname, stderr);
+	fputs(": ", stderr);
+}
+
+/* Issue a warning, then die */
+__attribute__(( noreturn, format (printf, 1, 2) ))
+static void error(const char* formatstr, ...) {
+	va_list ap;
+	va_start(ap, formatstr);
+	warning_prefix();
+	vfprintf(stderr, formatstr, ap);
+	va_end(ap);
+	exit(1);
+}
+
+/* Issue a warning, then die, with errno */
+__attribute__(( noreturn ))
+static void error_with_errno(const char* message) {
+	int saved_errno;
+	saved_errno=errno;
+	warning_prefix();
+	fputs(message, stderr);
+	fputs(": error number ", stderr);
+	fprintf(stderr, "%i\n", saved_errno);
+	exit(1);
+}
+
+/* Convert 'wait'/'system'-style exit status to 'exit'-style exit status */
+__attribute__(( const ))
+static int shorten_status(int status_big) {
+	if (WIFEXITED(status_big))
+		return WEXITSTATUS(status_big);
+	if (WIFSIGNALED(status_big))
+		return 128+WTERMSIG(status_big);
+	if (WIFSTOPPED(status_big))
+		return 128+WSTOPSIG(status_big);
+#ifdef WCOREDUMP
+	if (WCOREDUMP(status_big))
+		 error("Ow, somebody dumped core!");
+#endif
+	error("shorten_status got an invalid status (?!)");
+}
+
+/* All the work for command 2. */
+__attribute__(( noreturn ))
+static void subprocess2(const char* cmd) {
+	/* Close the old standard input. */
+	if (close(0))
+		error_with_errno("Failed (in child) closing standard input");
+	/* Make the reading end of the pipe the new standard input. */
+	if (dup2(filedes[0], 0) == -1)
+		error_with_errno("Failed (in child) redefining standard input");
+	/* Close the other end of the pipe. */
+	if (close(filedes[1]))
+		error_with_errno("Failed (in child) closing filedes[1]");
+	/* Do the second command, and throw away the exit status. */
+	system(cmd);
+	/* Close all the file descriptors. */
+	if (close(filedes[0]))
+		error_with_errno("Failed (in child) closing filedes[0]"
+			" (while cleaning up)");
+	if (close(0))
+		error_with_errno("Failed (in child) closing standard output "
+			" (while cleaning up)");
+	exit(0);
+}
+
+int main (int argc, const char ** argv) {
+	int status_big; /* Exit status, 'wait' and 'system' style */
+	pid_t child2_pid;
+	pid_t dead_pid;
+
+	/* Set progname */
+	progname = argv[0];
+
+	/* Verify arguments */
+	if (argc != 3) 
+		error("Wrong number of args, aborting\n");
+	/* Open a new pipe */
+	if (pipe(filedes))
+		error_with_errno("pipe() failed");
+
+	/* Fork to run second command */
+	child2_pid = fork();
+	if (child2_pid == 0)
+		subprocess2(argv[2]);
+	if (child2_pid == -1)
+		error_with_errno("fork() failed");
+
+	/* Run first command inline (seriously!) */
+	/* Close standard output. */
+	if (close(1))
+		error_with_errno("Failed closing standard output");
+	/* Make the writing end of the pipe the new standard output. */
+	if (dup2(filedes[1], 1) == -1)
+		error_with_errno("Failed redefining standard output");
+	/* Close the other end of the pipe. */
+	if (close(filedes[0]))
+		error_with_errno("Failed closing filedes[0]");
+	/* Do the first command, and (crucially) get the status. */
+	status_big = system(argv[1]);
+
+	/* Close the pipe "standard output". */
+	if (close(filedes[1]))
+		error_with_errno("Failed closing filedes[1] (while cleaning up)");
+	/* Close standard output. */
+	if (close(1))
+		error_with_errno("Failed closing standard output (while cleaning up)");
+
+	/* Wait for the other process to exit. */
+	/* We don't care about the status. */
+	dead_pid = waitpid(child2_pid, NULL, WUNTRACED);
+	if (dead_pid == -1) {
+		error_with_errno("waitpid() failed");
+	}
+	else if (dead_pid != child2_pid) {
+		error("waitpid(): Who died? %i\n", dead_pid);
+	}
+
+	/* Return the desired exit status. */
+	return shorten_status(status_big);
+}