Use a two-sub strategy. The first is a sub that gets strings to be parsed out of anything: a filename, a ref to a scalar of data, a ref to an array of data, or a ref to a glob filehandle. Within your sub, do a check on ref($_[0]);. Set it up as follows:

• ref() returns false: The value should be used as a filename. Open the filename and parse the file.
• ref() returns SCALAR: The value should be used as a reference to a string to be parsed.
• ref() returns ARRAY: The value should be used as a ref to an array of strings to be parsed.
• ref() returns GLOB: The value should be used as a filehandle. Read from the filehandle and parse the file.

From any of those sources, the first sub will send string(s) to the parsing engine one at a time, which is a second sub. That parsing engine needs to only understand how to parse strings. It doesn't care whether it got that string from a filehandle or a scalar, because that's all handled by the invoking sub.