To calculate the SHA-1 sums, display them and make them available for download in a sums.gz file:
<?php echo(`find ./some_directory/ -type f | grep -v sums.gz | xargs sha1sum | gzip -c | tee sums.gz | zcat`); ?>
To check the sums:
<?php echo(`zcat sums.gz | sha1sum -c -`); ?>