redirecting standard output and standard error

s_gaurav1091 has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: redirecting standard output and standard error by Skeeve (Parson) on Sep 04, 2006 at 13:55 UTC
`open(STDERR, '>', '/dev/null'); system("/i/dont/exist")` [download] `s$$([},&%#}/&/]+}%&{});#$&&s&&$^X.($'^"%]=\&(\|?{%` `+`.+=%;.#_}\&"^"-+%*).}%:##%}={~=~:.")&e&&s""`$''`"e	[reply] [d/l] [select]
Re: redirecting standard output and standard error by shmem (Chancellor) on Sep 04, 2006 at 12:55 UTC
`my $rc = system("java -version >/dev/null 2>&1");` [download] 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°\ / /\_Ż/(q / ---------------------------- \__(m.====·.(_("always off the crowd"))."· ");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}	[reply] [d/l]
Re: redirecting standard output and standard error by holli (Abbot) on Sep 04, 2006 at 13:21 UTC
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/	[reply] [d/l]
Re^2: redirecting standard output and standard error by adrianh (Chancellor) on Sep 04, 2006 at 18:12 UTC
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.	[reply]
Re: redirecting standard output and standard error by graff (Chancellor) on Sep 04, 2006 at 15:06 UTC
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` [download] 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).	[reply] [d/l] [select]
Re^2: redirecting standard output and standard error by Skeeve (Parson) on Sep 04, 2006 at 15:44 UTC
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	[reply] [d/l] [select]
Re: redirecting standard output and standard error by OfficeLinebacker (Chaplain) on Sep 04, 2006 at 19:41 UTC
IPC::Run is the way to go IMO. _________________________________________________________________________________ I like computer programming because it's like Legos for the mind.	[reply]