Initial revision

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+/* env - run a program in a modified environment
+   Copyright (C) 1986, 1991 Free Software Foundation, Inc.
+
+   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, 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., 675 Mass Ave, Cambridge, MA 02139, USA.  */
+
+/* Richard Mlynarik and David MacKenzie */
+
+/* Options:
+   -
+   -i
+   --ignore-environment
+	Construct a new environment from scratch; normally the
+	environment is inherited from the parent process, except as
+	modified by other options.
+
+   -u variable
+   --unset=variable
+	Unset variable VARIABLE (remove it from the environment).
+	If VARIABLE was not set, does nothing.
+
+   variable=value (an arg containing a "=" character)
+	Set the environment variable VARIABLE to value VALUE.  VALUE
+	may be of zero length ("variable=").  Setting a variable to a
+	zero-length value is different from unsetting it.
+
+   --
+	Indicate that the following argument is the program
+	to invoke.  This is necessary when the program's name
+	begins with "-" or contains a "=".
+
+   The first remaining argument specifies a program to invoke;
+   it is searched for according to the specification of the PATH
+   environment variable.  Any arguments following that are
+   passed as arguments to that program.
+
+   If no command name is specified following the environment
+   specifications, the resulting environment is printed.
+   This is like specifying a command name of "printenv".
+
+   Examples:
+
+   If the environment passed to "env" is
+	{ LOGNAME=rms EDITOR=emacs PATH=.:/gnubin:/hacks }
+
+   env - foo
+	runs "foo" in a null environment.
+
+   env foo
+	runs "foo" in the environment
+	{ LOGNAME=rms EDITOR=emacs PATH=.:/gnubin:/hacks }
+
+   env DISPLAY=gnu:0 nemacs
+	runs "nemacs" in the envionment
+	{ LOGNAME=rms EDITOR=emacs PATH=.:/gnubin:/hacks DISPLAY=gnu:0 }
+
+   env - LOGNAME=foo /hacks/hack bar baz
+	runs the "hack" program on arguments "bar" and "baz" in an
+	environment in which the only variable is "LOGNAME".  Note that
+	the "-" option clears out the PATH variable, so one should be
+	careful to specify in which directory to find the program to
+	call.
+
+   env -u EDITOR LOGNAME=foo PATH=/energy -- e=mc2 bar baz
+	runs the program "/energy/e=mc2" with environment
+	{ LOGNAME=foo PATH=/energy }
+*/
+
+#include <stdio.h>
+#include <getopt.h>
+#include <sys/types.h>
+#include "system.h"
+
+int putenv ();
+void error ();
+void usage ();
+
+extern char **environ;
+
+/* The name by which this program was run. */
+char *program_name;
+
+struct option longopts[] =
+{
+  {"ignore-environment", 0, NULL, 'i'},
+  {"unset", 1, NULL, 'u'},
+  {NULL, 0, NULL, 0}
+};
+
+void
+main (argc, argv, envp)
+     register int argc;
+     register char **argv;
+     char **envp;
+{
+  char *dummy_environ[1];
+  int optc;
+  int ignore_environment = 0;
+
+  program_name = argv[0];
+
+  while ((optc = getopt_long (argc, argv, "+iu:", longopts, (int *) 0)) != EOF)
+    {
+      switch (optc)
+	{
+	case 'i':
+	  ignore_environment = 1;
+	  break;
+	case 'u':
+	  break;
+	default:
+	  usage ();
+	}
+    }
+
+  if (optind != argc && !strcmp (argv[optind], "-"))
+    ignore_environment = 1;
+  
+  environ = dummy_environ;
+  environ[0] = NULL;
+
+  if (!ignore_environment)
+    for (; *envp; envp++)
+      putenv (*envp);
+
+  optind = 0;			/* Force GNU getopt to re-initialize. */
+  while ((optc = getopt_long (argc, argv, "+iu:", longopts, (int *) 0)) != EOF)
+    if (optc == 'u')
+      putenv (optarg);		/* Requires GNU putenv. */
+
+  if (optind != argc && !strcmp (argv[optind], "-"))
+    ++optind;
+
+  while (optind < argc && index (argv[optind], '='))
+    putenv (argv[optind++]);
+
+  /* If no program is specified, print the environment and exit. */
+  if (optind == argc)
+    {
+      while (*environ)
+	puts (*environ++);
+      exit (0);
+    }
+
+  execvp (argv[optind], &argv[optind]);
+  error (errno == ENOENT ? 127 : 126, errno, "%s", argv[optind]);
+}
+
+void
+usage ()
+{
+  fprintf (stderr, "\
+Usage: %s [-] [-i] [-u name] [--ignore-environment] [--unset=name]\n\
+       [name=value]... [command [args...]]\n",
+	   program_name);
+  exit (2);
+}