Redirecting and using output from executed program

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

Hello monks,

I'm currently writing a wrapper to run another program. Now i run the program N times and reformat its output into another format. However the program that I run seems to output some useless lines into STDERR and i would like to get rid of these. I run the program like this:

# @exec has the commad that i wish to run
open (T_RES,"@exec |") or die "Unable to fork '@exec': $!";
while (<T_RES>) {
  # parsing the output
}
[download]

This allows the output parsing to read the T_RES as a file, which don't require me the save all the output into memory. However this way does not capture the STDERR. Is there a way to capture the STDERR in this way as well? Is there another way which would be as easily used and require little memory?

Comment on Redirecting and using output from executed program Download Code

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Re: Redirecting and using output from executed program by Velaki (Chaplain) on Sep 30, 2004 at 10:15 UTC
Two ways of doing this might be the shell redirect method `# @exec has the commad that i wish to run # but we're throwing away the error meesages open (T_RES,"@exec 2>/dev/null \|") or die "Unable to fork '@exec': $!"; while (<T_RES>) { # parsing the output }` [download] and the Perl IPC method `# @exec has the commad that i wish to run use IPC::Open3 my $pid; $pid = open (WTR,T_RES,ERR,"@exec") or die "Unable to fork '@exec': $!"; while (<T_RES>) { # parsing the output } waitpid $pid, 0; # if necessary, see below` [download] Thought the shell method might be easier, the IPC::Open3 method might be more portable. Note: With the IPC::Open3 method, you might have to waitpid to reap the process. Hope that helped, -v "Perl. There is no substitute."	[reply] [d/l] [select]
Re^2: Redirecting and using output from executed program by DrHyde (Prior) on Sep 30, 2004 at 16:50 UTC
Or if you want to keep STDERR, `2>&1` instead of `2>/dev/null` would be nice. This may be sensitive to your choice of shell. Also try the IO::Capture modules.	[reply] [d/l] [select]
Re: Redirecting and using output from executed program by tachyon (Chancellor) on Sep 30, 2004 at 08:03 UTC
STDERR is file descriptor 2, STDOUT is descriptor 1. You can redirect it wherever you want: `# no redirection C:\>perl -e "warn 'foo'" foo at -e line 1. # redirect STDERR to FILE (often /dev/null :-) C:\>perl -e "warn 'foo'" 2> out C:\>type out foo at -e line 1. # redirect STDERR to STDOUT C:\>perl -e "warn 'foo'" 2>&1 foo at -e line 1. # redirect STDERR to STDOUT and STDOUT to FILE C:\>perl -e "warn 'foo';print 'bar'">out 2>&1 C:\>type out foo at -e line 1. bar` [download] cheers tachyon	[reply] [d/l]
Re^2: Redirecting and using output from executed program by Hena (Friar) on Sep 30, 2004 at 08:11 UTC
I don't want to redirect my own scripts STDERR anywhere (unless that is the only option, then obviously I must). I want to redirect/edit the STDERR from the program I execute. Every rediction must be done within script, as the script will be called by others programs eventually.	[reply]
Re^3: Redirecting and using output from executed program by tachyon (Chancellor) on Sep 30, 2004 at 08:13 UTC
It is no different within yor script, just `open (T_RES,"@exec 2>&1 \|")`	[reply] [d/l]
Re^4: Redirecting and using output from executed program by Hena (Friar) on Sep 30, 2004 at 08:22 UTC
Re^5: Redirecting and using output from executed program by tachyon (Chancellor) on Sep 30, 2004 at 08:27 UTC
Some notes below your chosen depth have not been shown here
Re: Redirecting and using output from executed program by insaniac (Friar) on Oct 01, 2004 at 11:12 UTC
Hey, I don't know if this is one of the best solutions, but I did it once like this: `open(LOG_FILE,">$log_file") \|\| die "Unable to open $log_file: $!\n"; my $old_err = STDERR; my $old_out = STDOUT; # Redirecting STDERR and STDOUT to the log file handle STDERR = \LOG_FILE; STDOUT = \LOG_FILE;` [download] and all standard print messages go to the log file, as well as all the error messages... yes, even the error messages of executed commands ;-) -- to ask a question is a moment of shame to remain ignorant is a lifelong shame	[reply] [d/l]