Shortest hex dumping program
C (gcc) on *nix, 73 71 bytes



i;main(c,v)int**v;{for(c=open(v[1],0);read(c,&amp;i,1);printf("%02X ",i));}


Try it online! Test suite

-2 bytes thanks to Johan du Toit

This relies on O_RDONLY == 0 and on int_one == 1 where int int_one; *(char*)&amp;int_one = 1;.