I'm looking for a library that will transform text files in one format into text files in another format. Example formats are XLS, XML, JSON, TSV, CSV, and various forms of fixed field length files.
I have a standard input format and a standard output format. Often, input files are in a different format and need to be transformed. Occasionally I'll also need to transform the output file before it can be used. These seems like a fairly common use case, so I don't want to reinvent the wheel if I can avoid it. Either this isn't as common as I think it is, or my Google-fu is failing me on this one. Most of the results are either online converters or single source/target converters (only CSV to JSON).
C# is preferable, although command-line option that I could invoke would work too. Open source or free is preferable, but all options are welcome.
P.S. I am aware that several ETL solutions do this sort of thing. I'm not looking for SSIS or Talend. I'm looking for a library or at least a command-line tool that I can invoke programmatically.