Thanks, krushnaal and Greg, By looking at the Greg's strace, it gives me great insight of the command.
So, It looks like it calls a library which can be in glib(?), and the library actually calls kernel device drivers like console or something like that, and they were communicating each other back and forth, and finally, it outputs the result of "ls" onto the screen. Is my understanding correct? Best Regards, Daniel (Youngwhan) Song On Wed, Dec 2, 2009 at 7:41 PM, Greg Freemyer <[email protected]>wrote: > On Wed, Dec 2, 2009 at 9:12 PM, Daniel (Youngwhan) Song > <[email protected]> wrote: > > Hi, > > > > Could somebody explain me how exactly "ls" command work in Unix/Linux? > > > > When we type "ls" command in linux shell, what does process/procedure > work > > with linux library or linux kernel, and how exactly does it show > directory > > information to the standard output (1)? > > > > Thanks in advance. > > > > Best Regards, > > Daniel Song > > > > read the source of course, but a very handy shortcut is: > > # strace ls > > The key part with a couple comments is: > > # Get the directory entries > open(".", O_RDONLY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY|O_CLOEXEC) = 3 > fcntl64(3, F_GETFD) = 0x1 (flags FD_CLOEXEC) > getdents64(3, /* 53 entries */, 32768) = 1744 > getdents64(3, /* 0 entries */, 32768) = 0 > close(3) = 0 > > # Verify stdout is a character device > fstat64(1, {st_mode=S_IFCHR|0600, st_rdev=makedev(136, 0), ...}) = 0 > > # map stdin into memory. (Not sure why, see the source) > mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, > 0) = 0xb73ff000 > > # write the directory entries to stdout and wrap-up > write(1, "bin Desktop Documents Downloa"..., 91bin Desktop > Documents Download Music Pictures Public public_html Templates > Videos > ) = 91 > close(1) = 0 > munmap(0xb73ff000, 4096) = 0 > close(2) = 0 > exit_group(0) = ? > > Greg >
