Argument are processed in the order they appear on the command line and are translated internally into a pipeline that data flows through when executed. Normally one would:

but GPSBabel is flexible enough to allow more complicated operations such as reading from several files (potentially of different types), applying a filter, reading more data, then write the merged data to multiple destinations.

The input file type remains unchanged until a new -i argument is seen. Files are read in the order they appear. So you could merge three input files into one output file with:

gpsbabel -i geo -f 1.loc -f 2.loc -f 3.loc -o geo -F big.loc

You can merge files of different types:

gpsbabel  -i geo -f 1.loc -i gpx -f 2.gpx -i pcx 3.pcx \ 
-o gpsutil -F big.gps

You can write the same data in different output formats:

gpsbabel -i geo -f 1.loc -o gpx -F 1.gpx -o pcx 1.wpt

If you want to change the character set of input or/and output side you can do this with the option -c <character set>. You can get a complete list of supported character sets with "gpsbabel -l". To change the character set on both sides you should do this:

gpsbabel -i xcsv,style=foo.style -c latin1 -f foo  \
	         -o xcsv,style=bar.style -c ms-ansi -F bar

Note, that some formats has a fixed character set and ignore this option.