10-19-2010
Well, in UNIX and shell, variable case is relevant, $HOME is not $home or $Home or $hOME, and some are very old choices, old like COBOL 68, before computers could afford lower case, so upper case is traditional for all env variables used by O/S or compiled code and other shared applications.
In your own private shell scripts, feel free to use lower case for your own data, without fear that you are accidentally turning on the $GO_AWAY_FOREVER option.
I can still hear those mainframers at AT&T, when I suggested encoding a flag byte with lower case for additional situations, mnemonicly, growling "You UNIX guys and your lower case!"
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Env(3pm) Perl Programmers Reference Guide Env(3pm)
NAME
Env - perl module that imports environment variables as scalars or arrays
SYNOPSIS
use Env;
use Env qw(PATH HOME TERM);
use Env qw($SHELL @LD_LIBRARY_PATH);
DESCRIPTION
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("
", @LD_LIBRARY_PATH), "
";
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;
LIMITATIONS
On VMS systems, arrays tied to environment variables are read-only. Attempting to change anything will cause a warning.
AUTHOR
Chip Salzenberg <chip@fin.uucp> and Gregor N. Purdy <gregor@focusresearch.com>
perl v5.12.1 2010-04-26 Env(3pm)