env.3

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.\" ========================================================================
.\"
.IX Title "Env 3"
.TH Env 3 "2007-12-18" "perl v5.10.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
Env \- perl module that imports environment variables as scalars or arrays
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 3
\&    use Env;
\&    use Env qw(PATH HOME TERM);
\&    use Env qw($SHELL @LD_LIBRARY_PATH);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
Perl maintains environment variables in a special hash named \f(CW%ENV\fR.  For
when this access method is inconvenient, the Perl module \f(CW\*(C`Env\*(C'\fR allows
environment variables to be treated as scalar or array variables.
.PP
The \f(CW\*(C`Env::import()\*(C'\fR function ties environment variables with suitable
names to global Perl variables with the same names.  By default it
ties all existing environment variables (\f(CW\*(C`keys %ENV\*(C'\fR) to scalars.  If
the \f(CW\*(C`import\*(C'\fR function receives arguments, it takes them to be a list of
variables to tie; it's okay if they don't yet exist. The scalar type
prefix '$' is inferred for any element of this list not prefixed by '$'
or '@'. Arrays are implemented in terms of \f(CW\*(C`split\*(C'\fR and \f(CW\*(C`join\*(C'\fR, using
\&\f(CW$Config::Config{path_sep}\fR as the delimiter.
.PP
After an environment variable is tied, merely use it like a normal variable.
You may access its value
.PP
.Vb 2
\&    @path = split(/:/, $PATH);
\&    print join("\en", @LD_LIBRARY_PATH), "\en";
.Ve
.PP
or modify it
.PP
.Vb 2
\&    $PATH .= ":.";
\&    push @LD_LIBRARY_PATH, $dir;
.Ve
.PP
however you'd like. Bear in mind, however, that each access to a tied array
variable requires splitting the environment variable's string anew.
.PP
The code:
.PP
.Vb 2
\&    use Env qw(@PATH);
\&    push @PATH, \*(Aq.\*(Aq;
.Ve
.PP
is equivalent to:
.PP
.Vb 2
\&    use Env qw(PATH);
\&    $PATH .= ":.";
.Ve
.PP
except that if \f(CW$ENV{PATH}\fR started out empty, the second approach leaves
it with the (odd) value "\f(CW\*(C`:.\*(C'\fR\*(L", but the first approach leaves it with \*(R"\f(CW\*(C`.\*(C'\fR".
.PP
To remove a tied environment variable from
the environment, assign it the undefined value
.PP
.Vb 2
\&    undef $PATH;
\&    undef @LD_LIBRARY_PATH;
.Ve
.SH "LIMITATIONS"
.IX Header "LIMITATIONS"
On \s-1VMS\s0 systems, arrays tied to environment variables are read-only. Attempting
to change anything will cause a warning.
.SH "AUTHOR"
.IX Header "AUTHOR"
Chip Salzenberg <\[e-mail]\fR>
and
Gregor N. Purdy <\[e-mail]\fR>