Putting files in an Array

[maheshkumar]

I am trying to put each line of a text file in an array, but encountering some problem with the logic. Can any one tell if the following logic is correct?

use warnings;
@ARGV = 'Google_1';
my @results;

while ( <ARGV> ){
    chomp $_;
      if($_ =~m/head/){
    push (@results, $_);
}
}
print "@results\n";

or can we use hash with these? My text file looks something like this but it has around 40k lines

192.168.178.1
82.135.16.28
212.18.7.101
212.18.6.166
80.81.192.28
92.123.72.112
82.135.16.28
212.18.7.101
212.18.6.77
217.71.108.93
217.71.96.169
194.59.190.3
134.222.231.49
134.222.229.49
134.222.229.205
134.222.229.222
134.222.231.22
62.41.85.112

[toolic]

but encountering some problem with the logic

Can you specify what problem you are having?

Since none of the lines of your text file have the string "head", you are not pushing any of those lines into your array. Try this:

use warnings;
use strict;

@ARGV = 'Google_1';
my @results;

while (<ARGV>) {
    chomp $_;
    push( @results, $_ );
}
print "@results\n";

[blue_cowdawg]

Personally for treating a file like an array I am a fan of using Tie::File

From the CPAN site:

# This file documents Tie::File version 0.98
        use Tie::File;

        tie @array, 'Tie::File', filename or die ...;

        $array[13] = 'blah';     # line 13 of the file is now 'blah'
        print $array[42];        # display line 42 of the file

        $n_recs = @array;        # how many records are in the file?
        $#array -= 2;            # chop two records off the end


        for (@array) {
          s/PERL/Perl/g;         # Replace PERL with Perl everywhere i
+n the file
        }

        # These are just like regular push, pop, unshift, shift, and s
+plice
        # Except that they modify the file in the way you would expect

        push @array, new recs...;
        my $r1 = pop @array;
        unshift @array, new recs...;
        my $r2 = shift @array;
        @old_recs = splice @array, 3, 7, new recs...;

        untie @array;            # all finished

Essentially anything you do with an array you can do with a file.

[kcott]

Your problem here seems to be that you're only pushing lines onto the array if they match /head/ but none of your sample lines match this. Result: empty array. Perhaps you meant !~ instead of =~.

It's difficult offering concrete advice here as your written explanantion "... put each line of a text file in an array ..." contradicts your code which is conditionally adding lines to the array. Furthermore, you'd probably get a better answer if we knew what you were planning to do with this array beyond print "@results\n";.

Maybe take a look at Tie::File. This will read all lines into an array in a single statement. The size of your file is not an issue with this module.

[cheekuperl]

I am trying to put each line of a text file in an array
All you need is this (after opening the file):

@lines=<FILEHANDLE> #slurp it

But I see your code conditionally pushes elements into array. Nothing seems wrong with the code. Two things:
1) Open file statement is missing.
2) Instead of using $_ everywhere, use your own variable.

[monsoon]

It looks like there's no need to open the file here, because the filename is in the @ARGV. It is as if it comes from STDIN. In this case this works @lines=<>;

[jethro]

ARGV in the while condition needs a '@'. Did you ever try to execute the script? UPDATE: Please ignore this line, I must have been in auto-destruct mode ;-). Thanks monsoon for the speedy correction

Naturally you could use a hash as well. Whether it works better with a hash or an array depends on what you need to do with the data. It also depends on the data. Since you only put lines into @results if they have "head" somewhere in the line and your example text file has not one line with "head" in it, an empty hash is as good as an empty array ;-)

PS: Your script seems to be a copy of a script suggested to you in this thread Out of Memory in Perl. I hope Zentara forgives me for saying this, but his advice to use @ARGVs magic just to read a file line by line is misleading. First of all it won't work to save memory by reading a file line by line if you then store it into an array anyway. And secondly you can read a file line by line without using @ARGV magic

Your original script (with the bug corrected) would have done the job as well.

[monsoon]

<@ARGV> won't work. ARGV is a special filehandle. See here

[zentara]

First of all it won't work to save memory by reading a file line by line if you then store it into an array anyway.

Sorry if I was misleading. In the original post, IIRC, he complained about filtering 2 gig files. The ARGV trick pushed matches into a @results array, and unless he had 2 gig's worth of matches, he should not run out of memory. In this node, he seems to want to slurp all lines into the array. I think that caused confusion, because in this node he wanted to use the ARGV trick on small files.

[zentara]

Sorry I mislead you with the line if($_ =~m/head/){}

It was just meant as an example regex. If you want to see how it works, with your test file try

 if($_ =~m/134/){  }

As others have pointed out, just to slurp a small file into an array, there are better ways than using <ARGV>. Your usage is Ok, but for small files you really don't need that type of code, as it was designed for line-by-line processing of huge files.

[Kenosis]

My text file looks something like this... (only IP addresses shown)

Perhaps I'm missing something, but you push a line onto an array if($_ =~m/head/), but there's no such match in the lines you've shown, so none of those IPs would end up in the array. Were you, in fact, only interested in those lines with "head" in them?

Update: Ken was much faster at this observation...