🚀 go-pugleaf

don't know if this question fit the group.

I want to send a postscrip string to the printer using fprintf or printf ,
in console application, printf sends the string to screen, how can I send
them to printer ?

 I got an example :

<!--StartFragment-->
  puts("/espWL{");
  puts("  espPF setfont");
  printf("  espPL stringwidth pop dup 12 add exch  -0.5 mul %.0f add\n",
         PageWidth * 0.5f);
  puts("  1 setgray");
  printf("  dup 6 sub %.0f 3 index 20 rectfill\n", PageBottom - 2.0);
  printf("  dup 6 sub %.0f 3 index 20 rectfill\n", PageTop - 18.0);
  puts("  0 setgray");
  printf("  dup 6 sub %.0f 3 index 20 rectstroke\n", PageBottom - 2.0);
  printf("  dup 6 sub %.0f 3 index 20 rectstroke\n", PageTop - 18.0);
  printf("  dup %.0f moveto espPL show\n", PageBottom + 2.0);
  printf("  %.0f moveto espPL show\n", PageTop - 14.0);
  puts("pop");
  puts("}bind def");

another example:

fprintf(fd, "newpath\n");
fprintf(fd, "%d %d moveto\n", x, y);
fprintf(fd, "%d 0  rlineto\n", wd);
fprintf(fd, "0 %d  rlineto\n", ht);
fprintf(fd, "-%d 0 rlineto\n", wd);
fprintf(fd, "closepath\n");
fprintf(fd, "stroke\n");


, I wonder how the computer know sending the postscript string to a printer
or a screen device ?