#! perl 
use strict;

my( $key, @array ) = split "\t", <>;
while( <> ) {
    chomp;
    my( $newKey, $value ) = split "\t";
    if( $newKey eq $key ) {
        push @array, $value;
        next;
    }
    else {
        # Process @array for $key      
        
        #...
        
        ## Remember the newKey
        $key = $nextKey;
        ## And the reset the array
        @array = $value;
    }
}


##</code><code>##

sort < unsortedFile | perl theScriptAbove

##</code><code>##

sort < unsortedFile > sortedFile
perl theScriptAbove sortedFile