If you want to concatenate multiple ps/pdf files into one large file use one of the following commands:

gs -dBATCH -dNOPAUSE -q -sDEVICE=pswrite -sOutputFile=merged.ps f1.ps f2.ps f3.ps

gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite -sOutputFile=merged.pdf f1.pdf f2.pdf f3.pdf