How is outputting to an array different from outputting to a file

kirk123 has asked for the wisdom of the Perl Monks concerning the following question:

Hi,

I am getting different result from accessing an array as oppose to reading from a file.

Earlier I was executing a unix command and reading the result like this:

system("lpstat -v -d -p -l -D >junk.txt");
open RI,"<junk.txt" || die "Can't open junk.txt for reading:$!\n";

my $data = do { local $/; <RI> }; # or however you load it.

my( %device, %system );

for ( split /\n(?=\S)/, $data )
{
  if( /^device for (.*?):.*?\1$/  )
  {
  
      $device{$1} = $1;
  }
  elsif ( /^system for (.*?): (\S+)/ )
  {
    $system{$1} = $2;
  }
[download]

------
--

But now I want to avoid opening and reading from a file so I use an array instead:

my @output =`lpstat -o -v -d -p -l -D`;.
my( %device, %system );
foreach my $line (@output) {
    chomp $line;

for ( split /\n(?=\S)/, $line )
{
  if  (/^system default/)
   {
     @test = split(/ /);
     chomp($test[3]);
     print "$test[3]|\n";
   } 
  if( /^device for (.*?):.*?\1$/  )
  {
  
      $device{$1} = $1;
  }
  elsif ( /^system for (.*?): (\S+)/ )
  {
    $system{$1} = $2;
  }
[download]

----
--
But by using an array I am getting a different answer than what I am getting by using a file.

How can I change my "array" code so that it works just like reading a file.

--thanks kirk123

20030218 Edit by Corion : Added formatting

Comment on How is outputting to an array different from outputting to a file Select or Download Code

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Re: How is outputting to an array different from outputting to a file by mojotoad (Monsignor) on Feb 17, 2003 at 01:02 UTC
You aren't really treating them the same by localizing the input record separator: `my $data = do { local $/; <RI> }; # or however you load it.` Instead try this: `@data = <RI>; chomp(@data);` [download] or `while ($line = <RI>) { chomp $line; ... }` [download] Then cycle through the data list. This is what you do in your array example. I suppose that answer is a bit backwards, however. Once you get the data in list format, you no longer need the split that you were using due to having overridden the input record separator: `for ( split /\n(?=\S)/, $line )` [download] Instead just use: `for my $line (@lines) {` [download] Matt	[reply] [d/l] [select]
Re: How is outputting to an array different from outputting to a file by blokhead (Monsignor) on Feb 17, 2003 at 01:04 UTC
Your code definitely does not compile so it's not clear what you've really tried. Do you intend to have the second `for` loop inside the `foreach` loop? Your indentation suggests otherwise. You don't have a closing brace there (among other syntax errors). The short and long of it: replace this from the first snippet: `system("lpstat -v -d -p -l -D >junk.txt"); open RI,"<junk.txt" \|\| die "Can't open junk.txt for reading:$!\n"; my $data = do { local $/; <RI> }; # or however you load it.` [download] With this: my $data = `lpstat -v -d -p -l -D`; An array isn't really necessary. In fact, in your example you were putting the entire results of the command into only the first element of your array. blokhead	[reply] [d/l] [select]
Re: How is outputting to an array different from outputting to a file by graff (Chancellor) on Feb 17, 2003 at 02:10 UTC
In order to make the second case work like the first one, you need to have the back-tick command assign its value to a scalar, rather than to an array: my $data =`lpstat -o -v -d -p -l -D`;. [download] In other words, if your first example (reading from the file) actually works, then all you need to do is replace these lines: `system("lpstat -v -d -p -l -D >junk.txt"); open RI,"<junk.txt" \|\| die "Can't open junk.txt for reading:$!\n"; my $data = do { local $/; <RI> };` [download] with the one back-tick line I showed above, and everything else should stay the same and still work.	[reply] [d/l] [select]
Re: How is outputting to an array different from outputting to a file by dws (Chancellor) on Feb 17, 2003 at 01:32 UTC
I am getting different result from accessing an array as oppose to reading from a file. Observation: You're not chomp'ing in the first case, and over-chomp'ing in the second.	[reply]
Re: How is outputting to an array different from outputting to a file by manux (Initiate) on Feb 18, 2003 at 14:08 UTC
you can also do: open ( RI,"lpstat -v -d -p -l -D \|") \|\| die "Can't run lpstat:$!\n"; my $data = do { local $/; <RI> }; # or however you load it. (but in this case is better $data=`lpstat -v -d -p -l -D`...unless you modify the script and you work on lpstat output line by line)	[reply]