use strict;
use warnings;

my @files;
my @ext = (qw{fb gdb ib fdb});

my $data = "/opt/databases/";                     # notice the final /

foreach my $ext (@ext) {
    my @load = glob "$data*.$ext";
    push (@files, @load);
}

foreach my $db (@files) {
    if (-f $db) {
        print "Found database: $db \n";
    }
    else {
        print "skiping '$db'...\n";
    }
}

# Alternatively:

foreach my $ext (@ext) {
    my @load = glob "$data*.$ext";
    foreach my $file (@load) {
        if (-f $file) {
            push (@files, $file);
        }
        else {
            print "Something is wrong, with '$file'!\n";
        }
    }
}

foreach my $db (@files) {
    print "Found database: $db \n";
}