Perl extension to manipulate MAchine Readable Cataloging recordshttp://search.cpan.org/perldoc?MARC
MARC.pm is a Perl 5 module for reading in, manipulating, and outputting bibliographic records in the USMARC format. You will need to have Perl 5.004 or greater for MARC.pm to work properly. Since it is a Perl module you use MARC.pm from one of your own Perl scripts. To see what sorts of conversions are possible you can try out a web interface to MARC.pm which will allow you to upload MARC files and retrieve the results (for details see the section below entitled "Web Interface").
However, to get the full functionality you will probably want to install MARC.pm on your server or PC. MARC.pm can handle both single and batches of MARC records. The limit on the number of records in a batch is determined by the memory capacity of the machine you are running. If memory is an issue for you MARC.pm will allow you to read in records from a batch gradually. MARC.pm also includes a variety of tools for searching, removing, and even creating records from scratch.