Re: shell and output redirection

On 07/02/2004 02:57:21 PM, Ganesh.Raja_at_barclayscapital.com wrote:
> They are Not Run ||'el... The utput of the first program is stored before
> the second is executed...

Not true. Here is the trace:

read(0, "l", 1) = 1
write(2, "l", 1) = 1
rt_sigprocmask(SIG_BLOCK, NULL, [RTMIN], 8) = 0 read(0, "s", 1) = 1
write(2, "s", 1) = 1
rt_sigprocmask(SIG_BLOCK, NULL, [RTMIN], 8) = 0 read(0, "|", 1) = 1
write(2, "|", 1) = 1
rt_sigprocmask(SIG_BLOCK, NULL, [RTMIN], 8) = 0 read(0, "s", 1) = 1
write(2, "s", 1) = 1
rt_sigprocmask(SIG_BLOCK, NULL, [RTMIN], 8) = 0 read(0, "o", 1) = 1
write(2, "o", 1) = 1
rt_sigprocmask(SIG_BLOCK, NULL, [RTMIN], 8) = 0 read(0, "e", 1) = 1
write(2, "e", 1) = 1
rt_sigprocmask(SIG_BLOCK, NULL, [RTMIN], 8) = 0 read(0, "\10", 1) = 1
write(2, "\10 \10", 3) = 3
rt_sigprocmask(SIG_BLOCK, NULL, [RTMIN], 8) = 0 read(0, "e", 1) = 1
write(2, "e", 1) = 1
rt_sigprocmask(SIG_BLOCK, NULL, [RTMIN], 8) = 0 read(0, "\10", 1) = 1
write(2, "\10 \10", 3) = 3
rt_sigprocmask(SIG_BLOCK, NULL, [RTMIN], 8) = 0 read(0, "r", 1) = 1
rt_sigprocmask(SIG_BLOCK, ~[], [RTMIN], 8) = 0 rt_sigprocmask(SIG_SETMASK, [RTMIN], NULL, 8) = 0 write(2, "r", 1) = 1
rt_sigprocmask(SIG_BLOCK, NULL, [RTMIN], 8) = 0 read(0, "t", 1) = 1
write(2, "t", 1) = 1
rt_sigprocmask(SIG_BLOCK, NULL, [RTMIN], 8) = 0 read(0, "\r", 1) = 1
write(2, "\n", 1) = 1

/* Read "ls|sort" from terminal screen */

pipe([3, 4]) = 0
rt_sigprocmask(SIG_BLOCK, [INT CHLD], [CHLD RTMIN], 8) = 0 pipe([5, 6]) = 0
fork() = 9430
setpgid(9430, 9430) = 0
rt_sigprocmask(SIG_SETMASK, [CHLD RTMIN], NULL, 8) = 0 close(4) = 0
close(4) = -1 EBADF (Bad file descriptor) rt_sigprocmask(SIG_BLOCK, [INT CHLD], [CHLD RTMIN], 8) = 0 fork() = 9431

/* Create two pipes and fork two processes */

wait4(-1, [WIFEXITED(s) && WEXITSTATUS(s) == 0], 0, NULL) = 9429 /* Wait for the output. Exec calls in the 2 forked processes weren't visible */

-- 
Mladen Gogala
Oracle DBA



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