Question

Based on the answer provided here, I am attempting to validate whether or not a perl module is installed.
For this, I have:

# &getYN and &prompt are only included here for completeness
sub getYN {
    unless ( $autoyes =~ /[Yy]/ ) {
        my ( $prompt, $default ) = @_;
        my $defaultValue = $default ? "[$default]" : "";
        print "$prompt $defaultValue: ";
        chomp( my $input = <STDIN> );
        return $input ? $input : $default;
    } else {
        return "Y";
    }
}

sub prompt {
    my ( $prompt, $default ) = @_;
    my $defaultValue = $default ? "[$default]" : "";
    print "$prompt $defaultValue: ";
    chomp( my $input = <STDIN> );
    return $input ? $input : $default;
}

&chklib("RRDTool::OO");
sub chklib {
    my $lib = shift;
    eval { require $lib; };
    if ($@) {
        print "You are missing a required Perl Module: $lib\n";
        my $ok = &getYN( "Shall I attempt to install it for you?", "y" );
        if ( $ok =~ /[Yy]/ ) {
            require CPAN;
            CPAN::install($lib);
        } else {
            print "Installation requires $lib\n";
            exit;
        }
    }
}

This runs as expected, but for some reason, the eval returns that I don’t have RRDTool::OO installed, when, in fact, I do.

If I create an empty file and run:

# File foo.pl
use strict;

$| = 1; 

use RRDTool::OO;

Then I get no errors.

But when I run the first file with print $@;, it returns:

Can't locate RRDTool::OO in ...

What am I doing wrong?

Answer 1

You have to check the result of the eval, like

if (eval("require xxx;")) {
     print "you have it\n";
} else {
     print "you don't\n";
}