new pwdx command

pwdx.c

@@ -0,0 +1,95 @@
+// Copyright 2004 Nicholas Miell
+//
+// This file may be used subject to the terms and conditions of the
+// GNU Library General Public License Version 2 as published by the
+// Free Software Foundation.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 Library General Public License for more
+// details.
+
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <regex.h>
+#include <limits.h>
+#include <unistd.h>
+#include <errno.h>
+
+#include "proc/version.h"
+
+static void die(const char *msg) NORETURN;
+static void die(const char *msg)
+{
+     fprintf(stderr, msg);
+     exit(1);
+}
+
+static void version(void) NORETURN;
+static void version(void)
+{
+     printf("pwdx (%s)\n", procps_version);
+     exit(0);
+}
+
+int main(int argc, char* argv[])
+{
+     char buf[PATH_MAX];
+     regex_t re;
+     int i;
+
+     if (argc < 2)
+          die("Usage: pwdx pid...\n");
+
+     // Allowed on the command line:
+     //
+     // --version
+     // -V
+     // /proc/nnnn
+     // nnnn
+     //
+     // where nnnn is any number that doesn't begin with 0.
+     //
+     // If --version or -V are present, further arguments are ignored
+     // completely.
+        
+     regcomp(&re, "^((/proc/+)?[1-9][0-9]*|-V|--version)$",
+             REG_EXTENDED|REG_NOSUB);
+
+     for (i = 1; i < argc; i++) {
+          if (regexec(&re, argv[i], 0, NULL, 0) != 0) {
+               sprintf(buf, "pwdx: invalid process id: %s\n", argv[i]); // FIXME (overflow)
+               die(buf);
+          }
+          if (!strcmp("-V", argv[i]) || !strcmp("--version", argv[i]))
+               version();
+     }
+
+     regfree(&re);
+
+     for (i = 1; i < argc; i++) {
+          char * s = buf;
+          int len;
+          
+          // At this point, all arguments are in the form /proc/nnnn
+          // or nnnn, so a simple check based on the first char is
+          // possible
+          if (argv[i][0] != '/')
+               sprintf(buf, "/proc/%s/cwd", argv[i]);
+          else
+               sprintf(buf, "%s/cwd", argv[i]);
+
+          // buf contains /proc/nnnn/cwd symlink name on entry, the
+          // target of that symlink on return
+          if ((len = readlink(buf, buf, PATH_MAX)) < 0) {
+               s = strerror(errno == ENOENT ? ESRCH : errno);
+          } else {
+               buf[len] = 0;
+          }
+
+          printf("%s: %s\n", argv[i], s);
+     }
+
+     return 0;
+}