#! /usr/bin/perl

use strict;
use warnings;

my @directories = qw{/foo /bar};
my $directory;
my @files;

while ( 1 ) {
    
    FILECHECK:
    foreach $directory ( @directories ) {
        
        @files = glob("${directory}/*.log");
        next FILECHECK unless @files;

        do some stuff here...
    }

    sleep 30;

}