#!/usr/bin/perl
#
# Become user; bypass shell.	- Cameron Simpson, 02may94
#
# Bug: doesn't fiddle with secondary groups at all.
#

($cmd=$0) =~ s:.*/::;
$usage="Usage: $cmd user [-g gid] [-s shell] [-ls|-c sh-command]
	-g gid		Specify GID instead of consulting passwd file.
	-s shell	Specify shell to run.
	-ls		Run a login shell.
	-c command	Run \"sh -c command\" (or other shell as specified).
";

$shell='/bin/sh';
$dologin=0;
undef $command;
undef $withgid;
undef $user;
@SHELLARGS=();

$badopts=0;
ARGV:
  while (defined($_=shift))
	{ if (!/^-/)
		{ if (defined $user)
			{ unshift(@ARGV,$_);
			  last ARGV;
			}
		  
		  $user=$_;
		  next ARGV;
		}

	  last ARGV if $_ eq '--';

	  if ($_ eq '-s')	{ $shell=shift; }
	  elsif ($_ eq '-g')	{ $withgid=shift; }
	  elsif ($_ eq '-ls')	{ $dologin=1; }
	  elsif ($_ eq '-c')	{ @SHELLARGS=('-c',shift); }
	  else
	  { print STDERR "$cmd: $_: unrecognised option\n";
	    $badopts=1;
	  }
	}

if ($#ARGV >= $[)
	{ print STDERR "$cmd: extra arguments: @ARGV\n";
	  $badopts=1;
	}

if (!defined $user)
	{ print STDERR "$cmd: missing user name\n";
	  $badopts=1;
	}

die $usage if $badopts;

if ($user =~ /^#(\d+)$/)
	{ ($login,$passwd,$uid,$gid,
           $quota,$comment,$gcos,$dir,$ushell) = getpwuid($1);
	}
else
{ ($login,$passwd,$uid,$gid,
   $quota,$comment,$gcos,$dir,$ushell) = getpwnam($user);
}

die "$cmd: who is $user?\n" unless defined($login);

eval '$(=$gid'; warn $@ if $@;
$)=$gid;
eval '$<=$uid'; warn $@ if $@;
$>=$uid;
($<,$()=($uid,$gid);
($>,$))=($uid,$gid);

if ($dologin)
	{ die "$cmd: can't cd to ~$login ($dir): $!\n" unless chdir $dir;
	  %ENV=(PATH,'/opt/bin:/usr/bin:/bin:/usr/ucb:/usr/bsd:.',
		HOME,$dir,
		USER,$login,
		SHELL,$shell,
		TERM,$ENV{TERM},
		ARCH,$ENV{ARCH});
	}

@ARGV=($dologin ? '-' : $shell, @SHELLARGS);

exec $shell @ARGV;
print STDERR "$cmd: can't execvp($shell @ARGV): $!\n";
exit 1;