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

Hi, I need to redirect stdout for a while in a subroutine, so I did this: 
sub generate_post 
{
        #need to redirect STDOUT
        open(SAVE_OUT, ">&", STDOUT);
        open(STDOUT, "> $POST_FILE") || die "Can't redirect stdout";
        more code goes here...
        #end of the subroutine:
        #need to restore STDOUT(!?)
        close(STDOUT);
        open(STDOUT, ">&", SAVE_OUT);

[download]
but this generates the following warning in perl v5.8.8: 
Name "main::SAVE_OUT" used only once: possible typo at ./part2.pl line
+ 332 (#1)
    (W once) Typographical errors often show up as unique variable nam
+es.
    If you had a good reason for having a unique name, then just menti
+on it
    again somehow to suppress the message.  The our declaration is
    provided for this purpose.
    
    NOTE: This warning detects symbols that have been used only once s
+o $c, @c,
    %c, *c, &c, sub c{}, c(), and c (the filehandle or format) are con
+sidered
    the same; if a program uses $c only once but also uses any of the 
+others it
    will not trigger this warning.

[download]
How can I get rid of this warning?

Replies are listed 'Best First'.
Re: getting rid of a warning
by moritz (Cardinal) on Jan 21, 2008 at 21:31 UTC
    You can use a lexical file handle: 
    open(my $save_out, '>&', STDOUT);

    [download]

    Or you can disable the warning in a small scope: 

    no warnings "once";

    [download]
[reply]
[d/l]
[select]
      Thank you, moritz. That was a stupid problem. Indeed, just using a "my $save_out" variable solved it.
[reply]
Re: getting rid of a warning
by hipowls (Curate) on Jan 21, 2008 at 21:38 UTC

    If you change use a lexical variable for for SAVE_OUT then the warning goes away. It is also safer, you never know when there will be another SAVE_OUT somewhere else in the code and data mysteriously disappears. 

    open( my $SAVE_OUT, ">&", STDOUT );
open( STDOUT, "> $POST_FILE" ) || die "Can't redirect stdout";

#more code goes here ...
#end of the subroutine:
#need to restore STDOUT(!?)
close(STDOUT);
open( STDOUT, ">&", $SAVE_OUT );

    [download]

    Update: There are some fast monks out there;)

[reply]
[d/l]
      >>If you change use a lexical variable for for SAVE_OUT then >>the warning goes away. It is also safer
      yep, that's right.
[reply]
Re: getting rid of a warning
by Jenda (Abbot) on Jan 22, 2008 at 04:25 UTC

    Are you sure you need to change the STDOUT? Any chance you actually need to change the select()ed filehandle? 

    open my $FH, '>', $POST_FILE or die "Can't redirect STDOUT";
my $oldFH = select($FH);
...
select($oldFH);

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    Of course this depends on whether you need to change the STDOUT for a subprocess or want to change where print "foo\n"; goes. In the later case you'd rather use the select(). Keep in mind that the select()ed filehandle may already be changed and then your STDOUT change will not have any effect.

    Jenda
    Support Denmark!
    Defend the free world!

[reply]
[d/l]
[select]
Re: getting rid of a warning
by aquarium (Curate) on Jan 21, 2008 at 21:38 UTC
    you could also do as the warning suggests
    SAVE_OUT;

    [download]
    should do the trick
    the hardest line to type correctly is: stty erase ^H
[reply]
[d/l]

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