The shell command spawns an interactive shell. To return to gnuplot, type logout if using VMS, exit or the END-OF-FILE character if using Unix, or exit if using MS-DOS or OS/2.
The shell command ignores anything else on the gnuplot command line. If instead you want to pass a command string to a shell for immediate execution, use the system function or the shortcut !. See system.
Examples:
shell system "print previous_plot.ps" ! print previous_plot.ps current_time = system("date")