From 32e75879103a943ac682cbde7b37ea4e4fbc24ab Mon Sep 17 00:00:00 2001
From: John Denker <jsd@av8n.com>
Date: Sat, 2 Jun 2012 09:07:44 -0700
Subject: add some tools

---
 tools/pido.c | 85 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 85 insertions(+)
 create mode 100644 tools/pido.c

(limited to 'tools/pido.c')

diff --git a/tools/pido.c b/tools/pido.c
new file mode 100644
index 0000000..9b92337
--- /dev/null
+++ b/tools/pido.c
@@ -0,0 +1,85 @@
+///////////////
+// pido
+// writes the pid, then execs something.
+//
+// Usage:
+//   pido pidfile /absolute/path/prog progarg1 progarg2 ...
+
+// If the first arg is missing or is "-" or is ""
+//   then we write to STDOUT.
+// If the first arg is "--" then we write to STDERR.
+// Otherwise the first arg is an ordinary filename.
+
+// Pido is important for scripts in init.d/ if they
+// want to start a pipeline.
+
+// If you use the command:
+//      aa | bb | cc &
+// then $! returns the pid of cc.
+// Alas, aa and/or bb may be just as important as cc
+// (or even more important).
+// For example, cc might be a simple logging utility,
+// while aa is the daemon of interest.
+//
+// It is often true BUT NOT PROVABLY TRUE that the pid
+// of bb is $! minus 1, and the pid of aa is $! minus 2.
+
+// If you want something provably correct, do this:
+//   pido /var/run/aa.pid /absolute/path/aa | bb | cc &
+// Then you know the correct pid of aa has been written
+// to the file aa.pid.
+
+// The perfect test for this is:
+//	 ./pido - ./pido -
+// which should print the same pid number twice.
+
+// There might be a way to do this with a simple shell script:
+//	echo ... exec ...
+// but if there is, I haven't figured it out.
+
+
+#include <unistd.h>
+#include <stdlib.h>		/* for exit() */
+#include <errno.h>
+#include <sys/types.h>		/* for fork(), wait() */
+#include <stdio.h>
+
+////////////////////////////////////////
+// Here with data coming in on fd 0.
+// and control coming in on ft 1.
+
+int main(int argc, char* argv[], char* env[]) {
+
+  FILE* ouch = stdout;
+  int isfile = 1;
+  if (argc > 1) {
+    if (argv[1][0] == '-' || argv[1][0] == 0) {
+      isfile = 0;
+      if (argv[1][1] == '-') ouch = stderr;
+    }
+    if (isfile) {
+      ouch = fopen (argv[1], "w");
+      if (!ouch) {
+        fprintf(stderr, "pido: cannot open pidfile '%s': ", argv[1]);
+        perror(0);
+        exit (1);
+      }
+    }
+  }
+
+  fprintf(ouch, "%d\n", getpid());
+
+  if (isfile) fclose(ouch);
+
+  if (argc > 2) {
+     execve(argv[2], argv+2, env);
+     fprintf(stderr, "pido: failed to exec '%s': ", argv[2]);
+     perror(0);
+     for (int ii = 0; ii < argc; ii++){
+       fprintf(stderr, "'%s' ", argv[ii]);
+     }
+     fprintf(stderr, "\n");
+     exit(2);
+  }
+  return 0;
+}
-- 
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