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exec, system, passthru problem -- wrong output!

P: n/a
I've found a problem with exec, passthru, shell_exec & system.

I'm trying to run the following

exec("sort -r -n -k2,2 r1.txt > r2.txt")

with r1.txt being a numeric file. The file looks like this:

237 291 845 152 585 3
193 810 173 484 151 3
366 491 910 265 893 3
220 631 571 332 104 3
502 567 854 40 108 3
639 13 720 101 482 3
254 676 896 759 720 3
907 928 377 899 778 3
324 194 995 161 708 3
501 936 716 105 209 3

(The file is actually 1500 lines long, but this gives you an idea.
It's tab delimited, and the numbers are random: I created the file
using awk to test this).

Here's the problem:
If I run it with exec, passthru, shell_exec or system, THE FILE GETS
TRUNCATED. Instead of 1500 lines, I get 1338. But if I run the SAME
COMMAND in the shell (manually), THE SORT WORKS OK!

I run this in other files and the result is the same: the file gets
truncated. Also, I checked for special characters, but there are none:
the file contains just regular numbers and tabs. The problem seems to
be PHP since when I run the command manually I get correct results...

Any ideas?

Thanks.
Jul 17 '05 #1
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3 Replies


P: n/a
Jerry23 wrote:
Iíve found a problem with exec, passthru, shell_exec & system.

Iím trying to run the following

exec("sort -r -n -k2,2 r1.txt > r2.txt")

with r1.txt being a numeric file. The file looks like this:

237 291 845 152 585 3
193 810 173 484 151 3
366 491 910 265 893 3
220 631 571 332 104 3
502 567 854 40 108 3
639 13 720 101 482 3
254 676 896 759 720 3
907 928 377 899 778 3
324 194 995 161 708 3
501 936 716 105 209 3

(The file is actually 1500 lines long, but this gives you an idea.
Itís tab delimited, and the numbers are random: I created the file
using awk to test this).

Hereís the problem:
If I run it with exec, passthru, shell_exec or system, THE FILE GETS TRUNCATED. Instead of 1500 lines, I get 1338. But if I run the SAME
COMMAND in the shell (manually), THE SORT WORKS OK!

I run this in other files and the result is the same: the file gets
truncated. Also, I checked for special characters, but there are none: the file contains just regular numbers and tabs. The problem seems to be PHP since when I run the command manually I get correct results...
Any ideas?

Thanks.

Sounds impossible. PHP simply passes the command to the shell, so I
cannot think of a reason it would be truncated. Are you sure, very
weird. The only thing I can think of is that PHP puts some kind of
timing contraints on the command. Easy to test that, jut put a " &"
at the end of the command to have it run in the background, and not
subject to any timing constraints.

Another approach is to bring the output into php using the `---` as
in:
$a = `sort -r -n -k2,2 r1.txt`;
and see what $a looks like.

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Jul 17 '05 #2

P: n/a
steve wrote:
Jerry23 wrote:
>
> Hereís the problem:
> If I run it with exec, passthru, shell_exec or system, THE FILE GETS
> TRUNCATED. Instead of 1500 lines, I get 1338. But if I run the SAME
> COMMAND in the shell (manually), THE SORT WORKS OK!

Sounds impossible. PHP simply passes the command to the shell, so I
cannot think of a reason it would be truncated. Are you sure, very
weird. The only thing I can think of is that PHP puts some kind of
timing contraints on the command. Easy to test that, jut put a " &"
at the end of the command to have it run in the background, and not
subject to any timing constraints.


IIRC that won't remove the constraint - the process will get a SIGHUP on
timeout of the php script - you'd need to isolate it from the signal (with
nohup) or run it in a seperate process group (e.g. `at now
run_shell_command`)

HTH

C.
Jul 17 '05 #3

P: n/a
Colin McKinnon <co**************@andthis.mms3.com> wrote in message news:<cc*******************@news.demon.co.uk>...
steve wrote:
Jerry23 wrote:
>
> Here?s the problem:
> If I run it with exec, passthru, shell_exec or system, THE FILE GETS > TRUNCATED. Instead of 1500 lines, I get 1338. But if I run the SAME
> COMMAND in the shell (manually), THE SORT WORKS OK!

Sounds impossible. PHP simply passes the command to the shell, so I
cannot think of a reason it would be truncated. Are you sure, very
weird. The only thing I can think of is that PHP puts some kind of
timing contraints on the command. Easy to test that, jut put a " &"
at the end of the command to have it run in the background, and not
subject to any timing constraints.


IIRC that won't remove the constraint - the process will get a SIGHUP on
timeout of the php script - you'd need to isolate it from the signal (with
nohup) or run it in a seperate process group (e.g. `at now
run_shell_command`)

HTH

C.


Colin, Steve:

OK Here's the deal: when I run them with & at the end (background), I
get the correct output. When I run them without the & I get the files
truncated. It looks like there's a problem with timing constraints as
you guys suggested.
I'll be following this problem (post it in some php dev list so
they're aware of the problem, etc).

Thank you for your help.

Jerry.
Jul 17 '05 #4

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