On Wed, Dec 2, 2009 at 9:12 PM, Daniel (Youngwhan) Song
<breadncup@xxxxxxxxx> 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
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