Cwd - get pathname of current working directory

    use Cwd;
    my $dir = getcwd;

    use Cwd 'abs_path';
    my $abs_path = abs_path($file);

  use Cwd qw(chdir);

package Cwd;

use strict;
use Exporter;
use vars qw(@ISA @EXPORT @EXPORT_OK $VERSION);

$VERSION = '3.33';
my $xs_version = $VERSION;
$VERSION = eval $VERSION;

@ISA = qw/ Exporter /;
@EXPORT = qw(cwd getcwd fastcwd fastgetcwd);
push @EXPORT, qw(getdcwd) if $^O eq 'MSWin32';
@EXPORT_OK = qw(chdir abs_path fast_abs_path realpath fast_realpath);

# sys_cwd may keep the builtin command

# All the functionality of this module may provided by builtins,
# there is no sense to process the rest of the file.
# The best choice may be to have this in BEGIN, but how to return from BEGIN?

if ($^O eq 'os2') {
    local $^W = 0;

    *cwd                = defined &sys_cwd ? \&sys_cwd : \&_os2_cwd;
    *getcwd             = \&cwd;
    *fastgetcwd         = \&cwd;
    *fastcwd            = \&cwd;

    *fast_abs_path      = \&sys_abspath if defined &sys_abspath;
    *abs_path           = \&fast_abs_path;
    *realpath           = \&fast_abs_path;
    *fast_realpath      = \&fast_abs_path;

    return 1;
}

# Need to look up the feature settings on VMS.  The preferred way is to use the
# VMS::Feature module, but that may not be available to dual life modules.

my $use_vms_feature;
BEGIN {
    if ($^O eq 'VMS') {
        if (eval { local $SIG{__DIE__}; require VMS::Feature; }) {
            $use_vms_feature = 1;
        }
    }
}

# Need to look up the UNIX report mode.  This may become a dynamic mode
# in the future.
sub _vms_unix_rpt {
    my $unix_rpt;
    if ($use_vms_feature) {
        $unix_rpt = VMS::Feature::current("filename_unix_report");
    } else {
        my $env_unix_rpt = $ENV{'DECC$FILENAME_UNIX_REPORT'} || '';
        $unix_rpt = $env_unix_rpt =~ /^[ET1]/i; 
    }
    return $unix_rpt;
}

# Need to look up the EFS character set mode.  This may become a dynamic
# mode in the future.
sub _vms_efs {
    my $efs;
    if ($use_vms_feature) {
        $efs = VMS::Feature::current("efs_charset");
    } else {
        my $env_efs = $ENV{'DECC$EFS_CHARSET'} || '';
        $efs = $env_efs =~ /^[ET1]/i; 
    }
    return $efs;
}


# If loading the XS stuff doesn't work, we can fall back to pure perl
eval {
  if ( $] >= 5.006 ) {
    require XSLoader;
    XSLoader::load( __PACKAGE__, $xs_version);
  } else {
    require DynaLoader;
    push @ISA, 'DynaLoader';
    __PACKAGE__->bootstrap( $xs_version );
  }
};

# Must be after the DynaLoader stuff:
$VERSION = eval $VERSION;

# Big nasty table of function aliases
my %METHOD_MAP =
  (
   VMS =>
   {
    cwd			=> '_vms_cwd',
    getcwd		=> '_vms_cwd',
    fastcwd		=> '_vms_cwd',
    fastgetcwd		=> '_vms_cwd',
    abs_path		=> '_vms_abs_path',
    fast_abs_path	=> '_vms_abs_path',
   },

   MSWin32 =>
   {
    # We assume that &_NT_cwd is defined as an XSUB or in the core.
    cwd			=> '_NT_cwd',
    getcwd		=> '_NT_cwd',
    fastcwd		=> '_NT_cwd',
    fastgetcwd		=> '_NT_cwd',
    abs_path		=> 'fast_abs_path',
    realpath		=> 'fast_abs_path',
   },

   dos => 
   {
    cwd			=> '_dos_cwd',
    getcwd		=> '_dos_cwd',
    fastgetcwd		=> '_dos_cwd',
    fastcwd		=> '_dos_cwd',
    abs_path		=> 'fast_abs_path',
   },

   # QNX4.  QNX6 has a $os of 'nto'.
   qnx =>
   {
    cwd			=> '_qnx_cwd',
    getcwd		=> '_qnx_cwd',
    fastgetcwd		=> '_qnx_cwd',
    fastcwd		=> '_qnx_cwd',
    abs_path		=> '_qnx_abs_path',
    fast_abs_path	=> '_qnx_abs_path',
   },

   cygwin =>
   {
    getcwd		=> 'cwd',
    fastgetcwd		=> 'cwd',
    fastcwd		=> 'cwd',
    abs_path		=> 'fast_abs_path',
    realpath		=> 'fast_abs_path',
   },

   epoc =>
   {
    cwd			=> '_epoc_cwd',
    getcwd	        => '_epoc_cwd',
    fastgetcwd		=> '_epoc_cwd',
    fastcwd		=> '_epoc_cwd',
    abs_path		=> 'fast_abs_path',
   },

   MacOS =>
   {
    getcwd		=> 'cwd',
    fastgetcwd		=> 'cwd',
    fastcwd		=> 'cwd',
    abs_path		=> 'fast_abs_path',
   },
  );

$METHOD_MAP{NT} = $METHOD_MAP{MSWin32};


# Find the pwd command in the expected locations.  We assume these
# are safe.  This prevents _backtick_pwd() consulting $ENV{PATH}
# so everything works under taint mode.
my $pwd_cmd;
foreach my $try ('/bin/pwd',
		 '/usr/bin/pwd',
		 '/QOpenSys/bin/pwd', # OS/400 PASE.
		) {

    if( -x $try ) {
        $pwd_cmd = $try;
        last;
    }
}
my $found_pwd_cmd = defined($pwd_cmd);
unless ($pwd_cmd) {
    # Isn't this wrong?  _backtick_pwd() will fail if somenone has
    # pwd in their path but it is not /bin/pwd or /usr/bin/pwd?
    # See [perl #16774]. --jhi
    $pwd_cmd = 'pwd';
}

# Lazy-load Carp
sub _carp  { require Carp; Carp::carp(@_)  }
sub _croak { require Carp; Carp::croak(@_) }

# The 'natural and safe form' for UNIX (pwd may be setuid root)
sub _backtick_pwd {
    # Localize %ENV entries in a way that won't create new hash keys
    my @localize = grep exists $ENV{$_}, qw(PATH IFS CDPATH ENV BASH_ENV);
    local @ENV{@localize};
    
    my $cwd = `$pwd_cmd`;
    # Belt-and-suspenders in case someone said "undef $/".
    local $/ = "\n";
    # `pwd` may fail e.g. if the disk is full
    chomp($cwd) if defined $cwd;
    $cwd;
}

# Since some ports may predefine cwd internally (e.g., NT)
# we take care not to override an existing definition for cwd().

unless ($METHOD_MAP{$^O}{cwd} or defined &cwd) {
    # The pwd command is not available in some chroot(2)'ed environments
    my $sep = $Config::Config{path_sep} || ':';
    my $os = $^O;  # Protect $^O from tainting


    # Try again to find a pwd, this time searching the whole PATH.
    if (defined $ENV{PATH} and $os ne 'MSWin32') {  # no pwd on Windows
	my @candidates = split($sep, $ENV{PATH});
	while (!$found_pwd_cmd and @candidates) {
	    my $candidate = shift @candidates;
	    $found_pwd_cmd = 1 if -x "$candidate/pwd";
	}
    }

    # MacOS has some special magic to make `pwd` work.
    if( $os eq 'MacOS' || $found_pwd_cmd )
    {
	*cwd = \&_backtick_pwd;
    }
    else {
	*cwd = \&getcwd;
    }
}

if ($^O eq 'cygwin') {
  # We need to make sure cwd() is called with no args, because it's
  # got an arg-less prototype and will die if args are present.
  local $^W = 0;
  my $orig_cwd = \&cwd;
  *cwd = sub { &$orig_cwd() }
}


# set a reasonable (and very safe) default for fastgetcwd, in case it
# isn't redefined later (20001212 rspier)
*fastgetcwd = \&cwd;

# A non-XS version of getcwd() - also used to bootstrap the perl build
# process, when miniperl is running and no XS loading happens.
sub _perl_getcwd
{
    abs_path('.');
}

# By John Bazik
#
# Usage: $cwd = &fastcwd;
#
# This is a faster version of getcwd.  It's also more dangerous because
# you might chdir out of a directory that you can't chdir back into.
    
sub fastcwd_ {
    my($odev, $oino, $cdev, $cino, $tdev, $tino);
    my(@path, $path);
    local(*DIR);

    my($orig_cdev, $orig_cino) = stat('.');
    ($cdev, $cino) = ($orig_cdev, $orig_cino);
    for (;;) {
	my $direntry;
	($odev, $oino) = ($cdev, $cino);
	CORE::chdir('..') || return undef;
	($cdev, $cino) = stat('.');
	last if $odev == $cdev && $oino == $cino;
	opendir(DIR, '.') || return undef;
	for (;;) {
	    $direntry = readdir(DIR);
	    last unless defined $direntry;
	    next if $direntry eq '.';
	    next if $direntry eq '..';

	    ($tdev, $tino) = lstat($direntry);
	    last unless $tdev != $odev || $tino != $oino;
	}
	closedir(DIR);
	return undef unless defined $direntry; # should never happen
	unshift(@path, $direntry);
    }
    $path = '/' . join('/', @path);
    if ($^O eq 'apollo') { $path = "/".$path; }
    # At this point $path may be tainted (if tainting) and chdir would fail.
    # Untaint it then check that we landed where we started.
    $path =~ /^(.*)\z/s		# untaint
	&& CORE::chdir($1) or return undef;
    ($cdev, $cino) = stat('.');
    die "Unstable directory path, current directory changed unexpectedly"
	if $cdev != $orig_cdev || $cino != $orig_cino;
    $path;
}
if (not defined &fastcwd) { *fastcwd = \&fastcwd_ }


# Keeps track of current working directory in PWD environment var
# Usage:
#	use Cwd 'chdir';
#	chdir $newdir;

my $chdir_init = 0;

sub chdir_init {
    if ($ENV{'PWD'} and $^O ne 'os2' and $^O ne 'dos' and $^O ne 'MSWin32') {
	my($dd,$di) = stat('.');
	my($pd,$pi) = stat($ENV{'PWD'});
	if (!defined $dd or !defined $pd or $di != $pi or $dd != $pd) {
	    $ENV{'PWD'} = cwd();
	}
    }
    else {
	my $wd = cwd();
	$wd = Win32::GetFullPathName($wd) if $^O eq 'MSWin32';
	$ENV{'PWD'} = $wd;
    }
    # Strip an automounter prefix (where /tmp_mnt/foo/bar == /foo/bar)
    if ($^O ne 'MSWin32' and $ENV{'PWD'} =~ m|(/[^/]+(/[^/]+/[^/]+))(.*)|s) {
	my($pd,$pi) = stat($2);
	my($dd,$di) = stat($1);
	if (defined $pd and defined $dd and $di == $pi and $dd == $pd) {
	    $ENV{'PWD'}="$2$3";
	}
    }
    $chdir_init = 1;
}

sub chdir {
    my $newdir = @_ ? shift : '';	# allow for no arg (chdir to HOME dir)
    $newdir =~ s|///*|/|g unless $^O eq 'MSWin32';
    chdir_init() unless $chdir_init;
    my $newpwd;
    if ($^O eq 'MSWin32') {
	# get the full path name *before* the chdir()
	$newpwd = Win32::GetFullPathName($newdir);
    }

    return 0 unless CORE::chdir $newdir;

    if ($^O eq 'VMS') {
	return $ENV{'PWD'} = $ENV{'DEFAULT'}
    }
    elsif ($^O eq 'MacOS') {
	return $ENV{'PWD'} = cwd();
    }
    elsif ($^O eq 'MSWin32') {
	$ENV{'PWD'} = $newpwd;
	return 1;
    }

    if (ref $newdir eq 'GLOB') { # in case a file/dir handle is passed in
	$ENV{'PWD'} = cwd();
    } elsif ($newdir =~ m#^/#s) {
	$ENV{'PWD'} = $newdir;
    } else {
	my @curdir = split(m#/#,$ENV{'PWD'});
	@curdir = ('') unless @curdir;
	my $component;
	foreach $component (split(m#/#, $newdir)) {
	    next if $component eq '.';
	    pop(@curdir),next if $component eq '..';
	    push(@curdir,$component);
	}
	$ENV{'PWD'} = join('/',@curdir) || '/';
    }
    1;
}


sub _perl_abs_path
{
    my $start = @_ ? shift : '.';
    my($dotdots, $cwd, @pst, @cst, $dir, @tst);

    unless (@cst = stat( $start ))
    {
	_carp("stat($start): $!");
	return '';
    }

    unless (-d _) {
        # Make sure we can be invoked on plain files, not just directories.
        # NOTE that this routine assumes that '/' is the only directory separator.
	
        my ($dir, $file) = $start =~ m{^(.*)/(.+)$}
	    or return cwd() . '/' . $start;
	
	# Can't use "-l _" here, because the previous stat was a stat(), not an lstat().
	if (-l $start) {
	    my $link_target = readlink($start);
	    die "Can't resolve link $start: $!" unless defined $link_target;
	    
	    require File::Spec;
            $link_target = $dir . '/' . $link_target
                unless File::Spec->file_name_is_absolute($link_target);
	    
	    return abs_path($link_target);
	}
	
	return $dir ? abs_path($dir) . "/$file" : "/$file";
    }

    $cwd = '';
    $dotdots = $start;
    do
    {
	$dotdots .= '/..';
	@pst = @cst;
	local *PARENT;
	unless (opendir(PARENT, $dotdots))
	{
	    # probably a permissions issue.  Try the native command.
	    return File::Spec->rel2abs( $start, _backtick_pwd() );
	}
	unless (@cst = stat($dotdots))
	{
	    _carp("stat($dotdots): $!");
	    closedir(PARENT);
	    return '';
	}
	if ($pst[0] == $cst[0] && $pst[1] == $cst[1])
	{
	    $dir = undef;
	}
	else
	{
	    do
	    {
		unless (defined ($dir = readdir(PARENT)))
	        {
		    _carp("readdir($dotdots): $!");
		    closedir(PARENT);
		    return '';
		}
		$tst[0] = $pst[0]+1 unless (@tst = lstat("$dotdots/$dir"))
	    }
	    while ($dir eq '.' || $dir eq '..' || $tst[0] != $pst[0] ||
		   $tst[1] != $pst[1]);
	}
	$cwd = (defined $dir ? "$dir" : "" ) . "/$cwd" ;
	closedir(PARENT);
    } while (defined $dir);
    chop($cwd) unless $cwd eq '/'; # drop the trailing /
    $cwd;
}


my $Curdir;
sub fast_abs_path {
    local $ENV{PWD} = $ENV{PWD} || ''; # Guard against clobberage
    my $cwd = getcwd();
    require File::Spec;
    my $path = @_ ? shift : ($Curdir ||= File::Spec->curdir);

    # Detaint else we'll explode in taint mode.  This is safe because
    # we're not doing anything dangerous with it.
    ($path) = $path =~ /(.*)/;
    ($cwd)  = $cwd  =~ /(.*)/;

    unless (-e $path) {
 	_croak("$path: No such file or directory");
    }

    unless (-d _) {
        # Make sure we can be invoked on plain files, not just directories.
	
	my ($vol, $dir, $file) = File::Spec->splitpath($path);
	return File::Spec->catfile($cwd, $path) unless length $dir;

	if (-l $path) {
	    my $link_target = readlink($path);
	    die "Can't resolve link $path: $!" unless defined $link_target;
	    
	    $link_target = File::Spec->catpath($vol, $dir, $link_target)
                unless File::Spec->file_name_is_absolute($link_target);
	    
	    return fast_abs_path($link_target);
	}
	
	return $dir eq File::Spec->rootdir
	  ? File::Spec->catpath($vol, $dir, $file)
	  : fast_abs_path(File::Spec->catpath($vol, $dir, '')) . '/' . $file;
    }

    if (!CORE::chdir($path)) {
 	_croak("Cannot chdir to $path: $!");
    }
    my $realpath = getcwd();
    if (! ((-d $cwd) && (CORE::chdir($cwd)))) {
 	_croak("Cannot chdir back to $cwd: $!");
    }
    $realpath;
}

# added function alias to follow principle of least surprise
# based on previous aliasing.  --tchrist 27-Jan-00
*fast_realpath = \&fast_abs_path;


# --- PORTING SECTION ---

# VMS: $ENV{'DEFAULT'} points to default directory at all times
# 06-Mar-1996  Charles Bailey  bailey@newman.upenn.edu
# Note: Use of Cwd::chdir() causes the logical name PWD to be defined
#   in the process logical name table as the default device and directory
#   seen by Perl. This may not be the same as the default device
#   and directory seen by DCL after Perl exits, since the effects
#   the CRTL chdir() function persist only until Perl exits.

sub _vms_cwd {
    return $ENV{'DEFAULT'};
}

sub _vms_abs_path {
    return $ENV{'DEFAULT'} unless @_;
    my $path = shift;

    my $efs = _vms_efs;
    my $unix_rpt = _vms_unix_rpt;

    if (defined &VMS::Filespec::vmsrealpath) {
        my $path_unix = 0;
        my $path_vms = 0;

        $path_unix = 1 if ($path =~ m#(?<=\^)/#);
        $path_unix = 1 if ($path =~ /^\.\.?$/);
        $path_vms = 1 if ($path =~ m#[\[<\]]#);
        $path_vms = 1 if ($path =~ /^--?$/);

        my $unix_mode = $path_unix;
        if ($efs) {
            # In case of a tie, the Unix report mode decides.
            if ($path_vms == $path_unix) {
                $unix_mode = $unix_rpt;
            } else {
                $unix_mode = 0 if $path_vms;
            }
        }

        if ($unix_mode) {
            # Unix format
            return VMS::Filespec::unixrealpath($path);
        }

	# VMS format

	my $new_path = VMS::Filespec::vmsrealpath($path);

	# Perl expects directories to be in directory format
	$new_path = VMS::Filespec::pathify($new_path) if -d $path;
	return $new_path;
    }

    # Fallback to older algorithm if correct ones are not
    # available.

    if (-l $path) {
        my $link_target = readlink($path);
        die "Can't resolve link $path: $!" unless defined $link_target;

        return _vms_abs_path($link_target);
    }

    # may need to turn foo.dir into [.foo]
    my $pathified = VMS::Filespec::pathify($path);
    $path = $pathified if defined $pathified;
	
    return VMS::Filespec::rmsexpand($path);
}

sub _os2_cwd {
    $ENV{'PWD'} = `cmd /c cd`;
    chomp $ENV{'PWD'};
    $ENV{'PWD'} =~ s:\\:/:g ;
    return $ENV{'PWD'};
}

sub _win32_cwd {
    if (eval 'defined &DynaLoader::boot_DynaLoader') {
	$ENV{'PWD'} = Win32::GetCwd();
    }
    else { # miniperl
	chomp($ENV{'PWD'} = `cd`);
    }
    $ENV{'PWD'} =~ s:\\:/:g ;
    return $ENV{'PWD'};
}

*_NT_cwd = defined &Win32::GetCwd ? \&_win32_cwd : \&_os2_cwd;

sub _dos_cwd {
    if (!defined &Dos::GetCwd) {
        $ENV{'PWD'} = `command /c cd`;
        chomp $ENV{'PWD'};
        $ENV{'PWD'} =~ s:\\:/:g ;
    } else {
        $ENV{'PWD'} = Dos::GetCwd();
    }
    return $ENV{'PWD'};
}

sub _qnx_cwd {
	local $ENV{PATH} = '';
	local $ENV{CDPATH} = '';
	local $ENV{ENV} = '';
    $ENV{'PWD'} = `/usr/bin/fullpath -t`;
    chomp $ENV{'PWD'};
    return $ENV{'PWD'};
}

sub _qnx_abs_path {
	local $ENV{PATH} = '';
	local $ENV{CDPATH} = '';
	local $ENV{ENV} = '';
    my $path = @_ ? shift : '.';
    local *REALPATH;

    defined( open(REALPATH, '-|') || exec '/usr/bin/fullpath', '-t', $path ) or
      die "Can't open /usr/bin/fullpath: $!";
    my $realpath = <REALPATH>;
    close REALPATH;
    chomp $realpath;
    return $realpath;
}

sub _epoc_cwd {
    $ENV{'PWD'} = EPOC::getcwd();
    return $ENV{'PWD'};
}


# Now that all the base-level functions are set up, alias the
# user-level functions to the right places

if (exists $METHOD_MAP{$^O}) {
  my $map = $METHOD_MAP{$^O};
  foreach my $name (keys %$map) {
    local $^W = 0;  # assignments trigger 'subroutine redefined' warning
    no strict 'refs';
    *{$name} = \&{$map->{$name}};
  }
}

# In case the XS version doesn't load.
*abs_path = \&_perl_abs_path unless defined &abs_path;
*getcwd = \&_perl_getcwd unless defined &getcwd;

# added function alias for those of us more
# used to the libc function.  --tchrist 27-Jan-00
*realpath = \&abs_path;

1;