redirecting standard output and standard error (s_gaurav1091)

redirecting standard output and standard error

created: 2006-09-04 08:25:59

perlmonks

node
author

prlmnks

node
author

Hi Monks, I am struck up at a problem. I want to write a script in which I dont any error to be shown on the console.Pls look at the code for refrence.

my $rc = system("java -version 2>/dev/null");
print "$rc\n";

Now when I am running the srcipt and in case the error comes I want only $rc should be printed on screen. But the output is coming like UX:sh (sh): ERROR: java: Not found rc is 256 Can anyone pls sugget as how to hide this error.Thanx in advance

Re: redirecting standard output and standard error

shmem

created: 2006-09-04 08:55:31

perlmonks

prlmnks

my $rc = system("java -version >/dev/null 2>&1");

might do on UNIX/Linux (redirect STDOUT to /dev/null, redirect STDERR to STDOUT closing the STDERR filehandle).

--shmem

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}

Re: redirecting standard output and standard error

holli

created: 2006-09-04 09:21:48

perlmonks

prlmnks

IPC::Open2, IPC::Open3.
Though I'm still not sure what is the real difference between the two (despite some syntax stuff).

holli, /regexed monk/

Re^2: redirecting standard output and standard error

adrianh

created: 2006-09-04 14:12:19

perlmonks

prlmnks

Though I'm still not sure what is the real difference between the two (despite some syntax stuff).

Open2 - STDIN, STDOUT
Open3 - STDIN, STDOUT & STDERR

Although I would personally use IPC::Run3 module which has a much simpler API in my opinion.

Re: redirecting standard output and standard error

Skeeve

created: 2006-09-04 09:55:50

perlmonks

prlmnks

open(STDERR, '>', '/dev/null');
system("/i/dont/exist")

s$$([},&%#}/&/]+}%&{})*;#$&&s&&$^X.($'^"%]=\&(|?*{%
+.+=%;.#_}\&"^"-+%*).}%:##%}={~=~:.")&e&&s""`$''`"e

Re: redirecting standard output and standard error

graff

created: 2006-09-04 11:06:51

perlmonks

prlmnks

[Skeeve] has shown how to get rid of the stderr output from the system call.

The error message is saying that when "system()" invokes a shell to run your "java -version" command, the shell is unable to find an application called "java" in its current PATH. But I don't understand the "UX:" part.

What operating system and shell are you using? This might account for why the redirection didn't work as expected. On my bsd-based darwin OS, the first of the two commands below produces an error message on the console, but the second does not -- meanwhile, a freebsd system behaves differently:

perl -e 'system( "foo > junk" );
# prints:
# sh: line 1: foo: command not found (on darwin)
# foo: not found (on freebsd 6.1)

perl -e 'system( "foo > junk 2>/dev/null" );
# no output on darwin
# still prints "foo: not found" on freebsd

I'm not sure if that's a difference in how Perl was built on the two machines I happened to be using, or whether it's a matter of how the shells work.

It may also be relevant that the ability to redirect stderr and stdout separately is only available for Bourne-style shells (sh, bash, ksh, zsh); in "c-style" shells ("csh" and any others like it), you can redirect stdout, and you can have stderr included with stdout when redirecting stdout, and that's all you can do ( 2> errlog is not supported, which is a big reason why I never use csh).

Re^2: redirecting standard output and standard error

Skeeve

created: 2006-09-04 11:44:36

perlmonks

prlmnks

I guess system("something 2>/dev/null") should redirect the error output of "something". Not that of the shell calling "something" So I would expect the error to be displayed when "something" isn't available (the error is produced by the shell) and to be suppressed when "something" is available, but produces an error.

s$$([},&%#}/&/]+}%&{})*;#$&&s&&$^X.($'^"%]=\&(|?*{%
+.+=%;.#_}\&"^"-+%*).}%:##%}={~=~:.")&e&&s""`$''`"e

Re: redirecting standard output and standard error

OfficeLinebacker

created: 2006-09-04 15:41:30

perlmonks

prlmnks

IPC::Run is the way to go IMO.

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