package Env;

our $VERSION = '1.00';

=head1 NAME

Env - perl module that imports environment variables as scalars or arrays

=head1 SYNOPSIS

use Env;
use Env qw(PATH HOME TERM);
use Env qw($SHELL @LD_LIBRARY_PATH);

=head1 DESCRIPTION

Perl maintains environment variables in a special hash named C<%ENV>. For
when this access method is inconvenient, the Perl module C<Env> allows
environment variables to be treated as scalar or array variables.

The C<Env::import()> function ties environment variables with suitable
names to global Perl variables with the same names. By default it
ties all existing environment variables (C<keys %ENV>) to scalars. If
the C<import> function receives arguments, it takes them to be a list of
variables to tie; it's okay if they don't yet exist. The scalar type
prefix '$' is inferred for any element of this list not prefixed by '$'
or '@'. Arrays are implemented in terms of C<split> and C<join>, using
C<$Config::Config{path_sep}> as the delimiter.

After an environment variable is tied, merely use it like a normal variable.
You may access its value

@path = split(/:/, $PATH);
print join("\n", @LD_LIBRARY_PATH), "\n";

or modify it

$PATH .= ":.";
push @LD_LIBRARY_PATH, $dir;

however you'd like. Bear in mind, however, that each access to a tied array
variable requires splitting the environment variable's string anew.

The code:

use Env qw(@PATH);
push @PATH, '.';

is equivalent to:

use Env qw(PATH);
$PATH .= ":.";

except that if C<$ENV{PATH}> started out empty, the second approach leaves
it with the (odd) value "C<:.>", but the first approach leaves it with "C<.>".

To remove a tied environment variable from
the environment, assign it the undefined value

undef $PATH;
undef @LD_LIBRARY_PATH;

=head1 LIMITATIONS

On VMS systems, arrays tied to environment variables are read-only. Attempting
to change anything will cause a warning.

=head1 AUTHOR

Chip Salzenberg E<lt>F<[email protected]>E<gt>
and
Gregor N. Purdy E<lt>F<[email protected]>E<gt>

=cut

sub import {
my ($callpack) = caller(0);
my $pack = shift;
my @vars = grep /^[\$\@]?[A-Za-z_]\w*$/, (@_ ? @_ : keys(%ENV));
return unless @vars;

@vars = map { m/^[\$\@]/ ? $_ : '$'.$_ } @vars;

eval "package $callpack; use vars qw(" . join(' ', @vars) . ")";
die $@ if $@;
foreach (@vars) {
my ($type, $name) = m/^([\$\@])(.*)$/;
if ($type eq '$') {
tie ${"${callpack}::$name"}, Env, $name;
} else {
if ($^O eq 'VMS') {
tie @{"${callpack}::$name"}, Env::Array::VMS, $name;
} else {
tie @{"${callpack}::$name"}, Env::Array, $name;
}
}
}
}

sub TIESCALAR {
bless \($_[1]);
}

sub FETCH {
my ($self) = @_;
$ENV{$$self};
}

sub STORE {
my ($self, $value) = @_;
if (defined($value)) {
$ENV{$$self} = $value;
} else {
delete $ENV{$$self};
}
}

######################################################################

package Env::Array;

use Config;
use Tie::Array;

@ISA = qw(Tie::Array);

my $sep = $Config::Config{path_sep};

sub TIEARRAY {
bless \($_[1]);
}

sub FETCHSIZE {
my ($self) = @_;
my @temp = split($sep, $ENV{$$self});
return scalar(@temp);
}

sub STORESIZE {
my ($self, $size) = @_;
my @temp = split($sep, $ENV{$$self});
$#temp = $size - 1;
$ENV{$$self} = join($sep, @temp);
}

sub CLEAR {
my ($self) = @_;
$ENV{$$self} = '';
}

sub FETCH {
my ($self, $index) = @_;
return (split($sep, $ENV{$$self}))[$index];
}

sub STORE {
my ($self, $index, $value) = @_;
my @temp = split($sep, $ENV{$$self});
$temp[$index] = $value;
$ENV{$$self} = join($sep, @temp);
return $value;
}

sub PUSH {
my $self = shift;
my @temp = split($sep, $ENV{$$self});
push @temp, @_;
$ENV{$$self} = join($sep, @temp);
return scalar(@temp);
}

sub POP {
my ($self) = @_;
my @temp = split($sep, $ENV{$$self});
my $result = pop @temp;
$ENV{$$self} = join($sep, @temp);
return $result;
}

sub UNSHIFT {
my $self = shift;
my @temp = split($sep, $ENV{$$self});
my $result = unshift @temp, @_;
$ENV{$$self} = join($sep, @temp);
return $result;
}

sub SHIFT {
my ($self) = @_;
my @temp = split($sep, $ENV{$$self});
my $result = shift @temp;
$ENV{$$self} = join($sep, @temp);
return $result;
}

sub SPLICE {
my $self = shift;
my $offset = shift;
my $length = shift;
my @temp = split($sep, $ENV{$$self});
if (wantarray) {
my @result = splice @temp, $self, $offset, $length, @_;
$ENV{$$self} = join($sep, @temp);
return @result;
} else {
my $result = scalar splice @temp, $offset, $length, @_;
$ENV{$$self} = join($sep, @temp);
return $result;
}
}

######################################################################

package Env::Array::VMS;
use Tie::Array;

@ISA = qw(Tie::Array);

sub TIEARRAY {
bless \($_[1]);
}

sub FETCHSIZE {
my ($self) = @_;
my $i = 0;
while ($i < 127 and defined $ENV{$$self . ';' . $i}) { $i++; };
return $i;
}

sub FETCH {
my ($self, $index) = @_;
return $ENV{$$self . ';' . $index};
}

1;