• do myfile.pm unconditionally loads in and evaluates a file. require myfile.pm does it only if it hasn't been done already
• You must use a file name with do. You can use either a file name or a module name with require.
• Only require can be used to insist on a specific version of Perl
• do can be used to group multiple statements into a single expression.require can't. For example,
  • do {...} foreach ...
  • do {....} while {...}
  • eval {...} or do {...}

For more information, please see require and do.

Best, beth