sudo apt-get install gs pdftk
gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite -sOutputFile=done.pdf ./*.pdf
A Sketch of GhostScript.
gs starts the Ghostscript program. -dBATCH once Ghostscript processes the PDF files, it should exit. If you don't include this option, Ghostscript will just keep running. -dNOPAUSE forces Ghostscript to process each page without pausing for user interaction. -q stops Ghostscript from displaying messages while it works -sDEVICE=pdfwrite tells Ghostscript to use its built-in PDF writer to process the files. -sOutputFile=finished.pdf tells Ghostscript to save the combined PDF file with the specified name.