One possibility would be to split on white space, then manually loop through the array - if the array element starts with a letter, it is the hash key, and if the following array element starts with a digit, that is the value; otherwise the value would be [].

There are many ways to do so, and the solution (of course) depends on your requirements. Based on your example, try the following approach:

1. read the text-file into one string
2. split the string based on your delimiter (which seems to be a blank). This will give you an array
3. Pass through the array.
   • check if the current element is a key (a single letter in your example, use =~ /\w/)
   • if yes: check if the next element is a value
   • if yes: store the value to the hash (using the key identified before)
   • if no: store an empty value to the hash (using the key identified before)
   • continue with the next element

Of course you can optimize. And probably you have to adapt the algorithm - but I hope it gives you an idea!

my %hash; my $key;
while ($_= <$file>) {
    my @line= split;
    while (@line) {
        my $part= shift @line;
        if ($part=~/^\D/) { #does not begin with a number
            $key= $part; $hash{$key}=[];
        }
        else {
            $hash{$key}= split /,/,$part;
        }
    }
}
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Untested.

Your posting would look better if you surrounded code with <code> </code> tags by the way

Updated, forgot a loop

perl -MData::Dumper -e '$_=q[a 2 b 4,5,6 c d e 45,657,-67];@arr=split 
+/\s+/;do { $arr[$_]!~/\d+/ and splice(@arr,$_,0,[]) } for grep {($_%2
+)} 0 .. $#arr;(%hash)=@arr;print Dumper(\%hash)'
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$VAR1 = { 'e' => '45,657,-67', 'c' => [], 'a' => '2', 'b' => '4,5,6', 'd' => [] };

... only that the OP wanted to have a reference to an empty array for missing values, not an empty string; so we would should transfer the array by map { length ? $_ : [] } @arr at the end.

-- 
Ronald Fischer <ynnor@mm.st>

The fact that the OP seems to want anonymous arrays for all the values makes things a bit easier. You can return an AoA of key and (possibly empty) value parts from a global match in an anonymous subroutine. Pass this into a map to deal with the value string using split.

$ perl -MData::Dumper -E '
> $text = q{a 2 b 4,5,6 c d e 45,657,-67};
> %hash =
>    map { $_->[ 0 ] => [ split m{,}, $_->[ 1 ] ] }
>    sub {
>        push @arr, [ $1, $2 ]
>           while $_[ 0 ] =~ m{\s*([a-z])\s+([-,\d]*)}g;
>        return @arr;
>        }->( $text );
> say Data::Dumper->Dumpxs( [ \ %hash ], [ qw{ *hash } ] );'
%hash = (
          'e' => [
                   '45',
                   '657',
                   '-67'
                 ],
          'c' => [],
          'a' => [
                   '2'
                 ],
          'b' => [
                   '4',
                   '5',
                   '6'
                 ],
          'd' => []
        );
$
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I hope this is helpful.

Thanks so much for ur help....but suppos my text data is of hundreds of line...it is not always possible to make a hash array as u had made....them what can i do?

You can use the same code because the \s* and \s+ in the match will also cater for newline (and carriage return if on Windows) so extracting the key and value parts will still work.

$ perl -MData::Dumper -E '
> $text = <<EOT;
> a 2 b 4,5,6 c d e 45,657,-67
> f g 23,54 h 5 i j
> 286,71,90 k 7 l 72
> m 26,8 n
> EOT
> %hash =
>    map { $_->[ 0 ] => [ split m{,}, $_->[ 1 ] ] }
>    sub {
>        push @arr, [ $1, $2 ]
>           while $_[ 0 ] =~ m{\s*([a-z])\s+([-,\d]*)}g;
>        return @arr;
>        }->( $text );
> say Data::Dumper->Dumpxs( [ \ %hash ], [ qw{ *hash } ] );'
%hash = (
          'e' => [
                   '45',
                   '657',
                   '-67'
                 ],
          'n' => [],
          'a' => [
                   '2'
                 ],
          'm' => [
                   '26',
                   '8'
                 ],
          'd' => [],
          'j' => [
                   '286',
                   '71',
                   '90'
                 ],
          'l' => [
                   '72'
                 ],
          'c' => [],
          'k' => [
                   '7'
                 ],
          'h' => [
                   '5'
                 ],
          'b' => [
                   '4',
                   '5',
                   '6'
                 ],
          'g' => [
                   '23',
                   '54'
                 ],
          'f' => [],
          'i' => []
        );
$
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If your data is in a file then slurp the whole of the file into a scalar. Something like (using strictures and warnings):-

my $dataFile = q{/path/to/myDataFile};
my $text = do {
   open my $dataFH, q{<}, $dataFile
      or die qq{open: < $dataFile: $!\n};
   local $/;
   <$dataFH>;
   };
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I hope this answers your question.

Cheers,

JohnGG