Section: Perl Programmers Reference Guide (3perl)
Updated: 2019-04-20
Page Index


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


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



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

The "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 ("keys %ENV") to scalars. If the "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 "split" and "join", using $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 $ENV{PATH} started out empty, the second approach leaves it with the (odd) value "":."``, but the first approach leaves it with ''"."".

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

    undef $PATH;
    undef @LD_LIBRARY_PATH;



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


Chip Salzenberg <chip@fin.uucp> and Gregor N. Purdy <gregor@focusresearch.com>