On 10/6/14, 5:00 PM, Linda Walsh wrote:
>> You are working in a severely constrained environment.
> That isn't the problem: the assignment using a tmp file is:
>> strace -p 48785 -ff
> Process 48785 attached
> read(0, "\r", 1) = 1
> write(2, "\n", 1) = 1
> socket(PF_NETLINK, SOCK_RAW, 9) = 3
> sendmsg(3, {msg_name(12)={sa_family=AF_NETLINK, pid=0, groups=00000000},
> msg_iov(2)=[{"*\0\0\0d\4\1\0\0\0\0\0\0\0\0\0", 16}, {"read a b c d
> <<<${arr[@]}\0", 26}], msg_controllen=0, msg_flags=0}, 0) = 42
> close(3) = 0
> -----
> Um... it used a socket.. to transfer it, then it uses a tmp file on top
> of that?! :
Slow down and read the trace, espcially the data being transferred. This
is syslog saving the command.
> rt_sigaction(SIGINT, {0x4320b1, [], SA_RESTORER|SA_RESTART, 0x30020358d0},
> {0x4320b1, [], SA_RESTORER|SA_RESTART, 0x30020358d0}, 8) = 0
> open("/tmp/sh-thd-110678907923", O_WRONLY|O_CREAT|O_EXCL|O_TRUNC, 0600) = 3
> write(3, "one two three four", 18) = 18
> write(3, "\n", 1) = 1
> open("/tmp/sh-thd-110678907923", O_RDONLY) = 4
> close(3) = 0
> unlink("/tmp/sh-thd-110678907923") = 0
> fcntl(0, F_GETFD) = 0
> fcntl(0, F_DUPFD, 10) = 10
> fcntl(0, F_GETFD) = 0
> fcntl(10, F_SETFD, FD_CLOEXEC) = 0
> dup2(4, 0) = 0
> close(4) = 0
> ioctl(0, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS,
> 0x7fff85627820) = -1 ENOTTY (Inappropriate ioctl for device)
> lseek(0, 0, SEEK_CUR) = 0
> read(0, "one two three four\n", 128) = 19
> dup2(10, 0) = 0
> fcntl(10, F_GETFD) = 0x1 (flags FD_CLOEXEC)
> close(10) = 0
> -----
>
> Why in gods name would it use a socket (still of arguable overhead, when
> it could be done in a local lib), but THEN it duplicates the i/o in a file?
Read the trace. There's no duplication going on. The shell uses temp
files to implement here documents -- an implementation choice you may
disagree with under your peculiar circumstances but one that is simple
and general.
>> Maybe the best solution here is to move your script to a different part
>> of the boot sequence. If you run it after all the local file systems
>> have been mounted, then you should be able to create temporary files,
>> which in turns means << and <<< become available, should you need them.
> ----
> Theoretically, they ARE mounted.... What I think may be happening
> is that $TMP is not set so it is trying to open the tmp dir in:
>
> "//sh-thd-183928392381" -- a network address.
This is not a network address. The pathname you've shown is consistent
with TMPDIR being set to a single slash (TMPDIR=/), which is a directory
writable by the current user.
You might try setting TMPDIR=/tmp in your startup script.
> ---
> Correctness before elegance. 1), use memory before OS services.
> 2) use in-memory services before file services, 3) Don't use uninitialized
> variables (TMP) -- verify that they are sane values before usage.
> 4) don't use network for tmp when /tmp or /var/tmp would have worked just
> fine.
This is basically word salad.
> This type of redirection instructs the shell to read input from the
> current source until a line containing only delimiter (with no trailing
> blanks) is seen. All of the lines read up to that point are then used
> as the standard input for a command.
>
> "The current source" -- can be anything that input can be
> redirected from -- including memory.
In your case, the current source is the script, where the data appears.
> How could you use a seek in the middle of a HERE doc
> read?
Think about your use cases. Many programs check whether or not their
input is a seekable device so they can read more than one character at
a time.
> Not only that, it's just wrong. /dev/stdin most often comes from
> a tty which is not random access.
Again, it depends on your use cases. There are a number of programs
whose primary use is in a filter environment rather than directly by
a user at a terminal.
>>> Creating a tmp file to do an assignment, I assert is a bug.
You're still mixing a general capability with your use of that capability.
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU c...@case.edu http://cnswww.cns.cwru.edu/~chet/
