mshow: spawn a pager for interactive use

1 files changed, 98 insertions, 0 deletions

diff --git a/pipeto.c b/pipeto.c
new file mode 100644
index 0000000..77982e1
--- /dev/null
+++ b/pipeto.c
@@ -0,0 +1,98 @@
+#include <sys/wait.h>
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+pid_t
+pipeto(const char *cmdline)
+{
+	int pipe0[2];  // stdout -> stdin
+	int pipe1[2];  // child errno -> parent
+	pid_t pid;
+
+	if (pipe(pipe0) < 0)
+		return -1;
+	if (pipe(pipe1) < 0)
+		return -1;
+
+	pid = fork();
+	if (pid < 0) {
+		return -1;
+	} else if (pid == 0) {  // in child
+		close(pipe1[0]);
+		// close errno pipe on successful exec
+		fcntl(pipe1[1], F_SETFD, FD_CLOEXEC);
+
+		if (dup2(pipe0[0], 0) < 0)
+			exit(111);
+
+		close(pipe0[0]);
+		close(pipe0[1]);
+
+		// split cmdline, just on spaces
+		char *argv[16];
+		int argc = 0;
+		char *cp = strdup(cmdline);
+		if (!cp)
+			exit(111);
+		while (argc < 16 && *cp) {
+			argv[argc++] = cp;
+			cp = strchr(cp, ' ');
+			if (!cp)
+				break;
+			*cp++ = 0;
+			while (*cp == ' ')
+				cp++;			
+		}
+		argv[argc] = 0;
+
+		execvp(argv[0], argv);
+
+		// execvp failed, write errno to parent
+		long e = errno;
+		if (write(pipe1[1], &e, sizeof e) < 0)
+			exit(111);  // do a magic dance for gcc -Wunused-result
+		exit(111);
+	} else {  // in parent
+		close(pipe1[1]);
+
+		long e;
+		ssize_t n = read(pipe1[0], &e, sizeof e);
+		if (n < 0)
+			e = errno;
+		close(pipe1[0]);
+
+		if (n == 0) {
+			// child executed successfully, redirect stdout to it
+			if (dup2(pipe0[1], 1) < 0)
+				return -1;
+
+			close(pipe0[0]);
+			close(pipe0[1]);
+
+			return pid;
+		} else {
+			errno = e;
+			return -1;
+		}
+	}
+
+//	return pid;
+}
+
+int
+pipeclose(pid_t pid)
+{
+	int s;
+
+	fflush(0);
+	close(1);
+	waitpid(pid, &s, 0);
+	
+	return s;
+}