problem of filehandling

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

Hello Monks,

I wrote a program that reads from an input file and that write hte output to another file.To give it more versatility, I want to see if there is an argument specifying the pathes and names of the files otherwise to read from STDIN and STDOUT. I sort of successed in doing that even though I don't know if is the most beautiful code. I just have a warning I can't get rid of.

Example of code and error message provided

Here is an example I wrote just to show you, so it doesn't actually do anything. However it outputs the warning produces by the pragma diagnostics (so I know that if I would get rid of the pragma, I would get rid of the message, but is that moral :-) )

Here is the code

#!/usr/bin/perl -w

use strict;
use warnings;
use diagnostics;
use Benchmark;
use Getopt::Long qw(:config no_ignore_case bundling);

#defines variables
my $man = 0;
my $help = 0;
my $input;
my $output;
my @blubb;

my %options = (
    'help|h'     => \$help,
    'man'        => \$man,
    'input|i=s'  => \$input,
    'output|o=s'  => \$output,
  );

GetOptions(%options);

open STDIN, "<$input" or die "Can't open $input: $!" if $input;
while(<STDIN>)
{
  chomp;
  push @blubb, $_;
}
close STDIN if $input;

open STDOUT, ">$output" or die "Can't open $output: $!" if $output;
print join "\n", @blubb;
print "\n";
close STDOUT if $output;

exit 0;
[download]

And here is the error message

Filehandle STDIN reopened as STDOUT only for output at ex.pl line 36 (
+#1)
(W io) You opened for writing a filehandle that got the same filehandl
+e id
as STDIN. This occured because you closed STDIN previously.
[download]

I don't understand this error message as I don't touch STDIN at line 36.
Anyone has a clue about the reason?

Thanks in advance

--
jey

Comment on problem of filehandling Select or Download Code

Replies are listed 'Best First'.
Re: problem of filehandling by Abigail-II (Bishop) on Jan 27, 2004 at 13:33 UTC
What part of `This occured because you closed STDIN previously.` don't you understand? You do close `STDIN` two lines above it. As for opening STDIN yourself, you could make use of the magic of the open command. If you open a file called "-", Perl will read from standard input. For instance: `Getoptions (...); $input = "-" unless defined $input; open my $fh => $input or die $!; while (<$fh>) { ... }` [download] Abigail	[reply] [d/l]

Replies are listed 'Best First'.

Re: problem of filehandling
by Abigail-II (Bishop) on Jan 27, 2004 at 13:33 UTC

This occured because you closed STDIN previously.

STDIN

As for opening STDIN yourself, you could make use of the magic of the open command. If you open a file called "-", Perl will read from standard input. For instance:

Getoptions (...);
$input = "-" unless defined $input;
open my $fh => $input or die $!;
while (<$fh>) { ... }
[download]

Abigail

[reply]
[d/l]