Score:-1

Ubuntu

in perl, the command "system", using indirect object, redirection does not work, need help

Anton Wessel

6/14/23, 12:01 PM

I am running Kubuntu 20.04. The perl version is shown by perl -v to be

perl 5, version 30, subversion 0 (v5.30.0) built for x86_64-linux-gnu-thread-multi (with 50 registered patches, see perl -V

I have just made apt-get update and with Muon package manager I have all installed perl packages upgraded.

But after that, perl is 5 as before, I have not got perl 6.

My problem is not when I use the simple system command like

perl -we 'system("echo \"aaa\" > /tmp/WEx_args_file"); '

In this case the file is written.

But when using the indirect object way, like

perl -we ' @WE_args = ( "echo", " \"qqq\" > /tmp/WEx_args_file" ); $WE_retcod_system = system { $WE_args[0] } @WE_args; print "WE_retcod_system: ~", $WE_retcod_system, "~\n"; if($WE_retcod_system != 0) { die "\nsystem >>>YYY>>>@WE_args<<<YYY<<< failed: $?"; }; '

in this case the file is not written.

The displayed output is on screen:

"qqq" > /tmp/WEx_args_file

then follows

WE_retcode_system: ~0~

I have tried the indirect object way in many variations a whole day. I have not found a code the tmp file to be written.

Please, do anybody know a solution?

=====

In trying to proceed, I have found the very good

IPC::System::Simple

By means of this, my intention is to replace my backtick code

echo -n "qqq" | xxd -g1

with the capturex function, like

perl -we ' use IPC::System::Simple qw/capturex/; open(FHo, ">/tmp/Wex_args_file") or die; $WE_got_from_cpx = capturex("echo", "-n", ""qqq"", "|", "xxd -g1" ); print FHo "WE_got_from_cpx: ~", $WE_got_from_cpx, "~\n"; '

As far as I understood, this is the correct usage of capturex. But new problem, it does not work.

The command on the RHS of the pipe, i.e.

xxd -g1

is not executed but only copied. The result is

WE_got_from_cpx: ~"qqq" | xxd -g1~

I'm afraid that these modules in IPC::System::Simple are based on the leading point like the "indirect object" way that only the first argument is the executed command.

How can I use IPC::System::Simple to make the whole backtick function go?

Regards anton

0 + 0

command-line

perl

muru

6/14/23, 2:15 PM

Why did you pass `echo` as an argument by itself but combined `"qqq" > /tmp/WEx_args_file` into one argument?

Anton Wessel

6/14/23, 3:58 PM

The recommended, so called "indirect object" way implies that the command to be executed is written in such a format: must b

Anton Wessel

6/14/23, 4:07 PM

The recommended, so called "indirect object" way implies that the command to be executed is written in such a format: must be as predecessor before of the list follows, the list of command "system list". All intermediate writings do not work, except when reduced to my first case of simply sytem()..

raj

6/14/23, 7:12 PM

Using indirect object syntax, you are passing `"qqq" > /tmp/WEx_args_file` as an argument string to the `echo` command, so no wonder that the command prints exactly that. In the simple version, the argument is only `\"aaa\"`. Redirection (`> /tmp/WEx_args_file`) is **not** part of the argument string; it is handled by the shell before arguments are passed to the command. You need to find a way to handle redirection using indirect object syntax; this may be tricky, if possible at all, will probably involve some operations on file descriptors. I suggest asking on StackOverflow for that.

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: in perl, the command "system", using indirect object, redirection does not work, need help

TH: ใน perl คำสั่ง "ระบบ" โดยใช้วัตถุทางอ้อม การเปลี่ยนเส้นทางไม่ทำงาน ต้องการความช่วยเหลือ

RO: în perl, comanda „sistem”, folosind obiect indirect, redirecționarea nu funcționează, are nevoie de ajutor

RU: в perl команда "система", используя косвенный объект, перенаправление не работает, нужна помощь

VI: trong perl, lệnh "hệ thống", sử dụng đối tượng gián tiếp, chuyển hướng không hoạt động, cần trợ giúp

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