Hello, and welcome to perlmonks.

I want to write a perl script

Great. Then I suggest you get started. If you're not very familiar with perl, you might want to start with perlintro.

If you experience problems along the way, feel free to ask here, and make sure to show the code you have written, along with a description of what your problem is.

Hi tony_ucdavis,

I only recently started with Perl myself. The tutorials section has a lot of really good information on how to start writing scripts and programs. Also, see if you can find a copy of the book 'Learning Perl', I have found it very useful.

You'll want to use the open function to open the file, a while loop to read the data in, and the print function to write everything out. If you want to store the data first, you can use a hash.

Just for the fun of it:

$_=<>;
1 while (s/(\w)\s(\d+)(.*)(\s\1\s)(\d+)/$1." ".($2+$5).$3/e);
print
[download]

Example call:

$ cat test
a 1 b 3 c 5 a 2
$ ./samekey test
a 3 b 3 c 5
$ cat anothertest
a 1 b 3 c 5 a 2 a 3 b 3 c 5
$ ./samekey anothertest
a 6 b 6 c 10
[download]

Hi tony ucdavis,
In case, you think those who commented before now really do not what to help, please think again. What you labour to do will not only be yours but would give you a kind of chip on your shoulder and a well of satisfaction.
However, if you are still in doubt the following solve your problem:

use warnings;
use strict;

my %h;
chomp( my @arr = split /\s+?/, <DATA> );

my $key;

for (@arr) {
    if ( !/[[:digit:]]/ ) {
        $key = $_;
    }
    else {
        if ( $h{$key} ) {
            $h{$key} += $_;
        }
        else { $h{$key} = $_ }
    }
}

print $_, q[ ], $h{$_}, q[ ], for sort keys %h;

__DATA__
a 1 b 3 c 5 a 2
[download]