how do i redirect STDOUT, STDIN, or STDERR to a FILE?

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

Replies are listed 'Best First'.
Re: how do i redirect STDOUT, STDIN, or STDERR to a FILE? (A=B sucks) by tye (Sage) on Dec 28, 2011 at 20:24 UTC
Yes, actually there are quite a few good reasons to not do that. `open( LOG, ">>", "log.txt" ) or die "Can't' write to log.txt: $!\n"; STDOUT= LOG; print "Yay! This goes to log.txt! Success!\n"; # Reason 1: system("echo Boo, this goes to the old STDOUT"); # Reason 2: close STDOUT; print LOG "Boo, this goes nowhere but I didn't close LOG!\n"; # Reason 3: open STDOUT, '>>', 'newlog.txt' or die "Can't write to newlog.txt: $!\n"; system("echo Boo, this still goes to old STDOUT despite reopening");` [download] `STDOUT = LOG` makes STDOUT and LOG share the same file handle in a way that is problematic to sane lifespan control. It also hides the old file handle for STDOUT away in a dark place where it will still get used by all manner of things that correctly know that FD 1 is how you send "standard output". And since FD 1 is kept open by this hidden-away, still-open file handle, open's careful work to try to make "open STDOUT" and "open STDERR" work correctly (ie. to have the first impact FD 1 and the second impact FD 2) is forever thwarted. Just don't manipulate file handles by local()izing and/or overwriting perl globs. Lots of pain to be had there. And this goes doubly when dealing with the STD file handles. - tye	[reply] [d/l] [select]
Re: how do i redirect STDOUT, STDIN, or STDERR to a FILE? by ikegami (Patriarch) on Dec 28, 2011 at 17:45 UTC
Nope, but there are limitations to it. Anything that uses file descriptor 2 (e.g. system) to mean STDERR won't see your change. Better: `open(STDERR, ">log.txt")` [download]	[reply] [d/l]
Re: how do i redirect STDOUT, STDIN, or STDERR to a FILE? by mr.nick (Chaplain) on Dec 28, 2011 at 17:48 UTC
`open STDERR,">","stderr.log" or die $!; open STDOUT,">","stdout.log" or die $!;` [download] It's a bit more clear and obvious. Redirecting STDIN to a file makes no sense, but I suppose you could do: `open STDIN,"<","stdin.txt" or die $!; print while <>;` [download] But I'm not sure what the purpose of that would be. mr.nick ...	[reply] [d/l] [select]
Re: how do i redirect STDOUT, STDIN, or STDERR to a FILE? by NetWallah (Canon) on Dec 28, 2011 at 18:35 UTC
Here is a small module I wrote years ago.. Read more... (1109 Bytes) to use: `STDERR_REDIRECTOR::capture(); # Do stuff that writes to STDERR\|; STDERR_REDIRECTOR::release(); STDERR_REDIRECTOR::showcapture();` [download] "Battle not with trolls, lest ye become a troll; and if you gaze into the Internet, the Internet gazes also into you." -Friedrich Nietzsche: A Dynamic Translation	[reply] [d/l] [select]