Hi there
I have a file that looks something like this 
Z  5   89
Z  92  102
Z  103 123
Z  126 150

[download]
In a nutshell - the length of the 'Z item' corresponds to the numbers following it. For example, the first Z item starts at element 5 and ends at element 89, making it 84 elements in length.
I want to find out 1) how many Z items there are in a given file and 2) the length of each of these Z items. Which would be remarkably easy if it wasn't for the following:
In some cases, a particular Z item has been mistakingly broken up into two. These mistakes are instantly recognisable because the 'stop element' of one incorrectly assigned Z item will be followed instantly by another Z item for which the start element is only one number after the previous stop one.
For example 
Z  92  102
Z  103 123

[download]
Is in reality only one Z item, yet in the file its recognised as two.
In my perl script I want to count such incorrectly assigned Z items as only being one whereever necessary but I am at a bit of a loss as to how to do that.
I guess I'm looking for a way of 'rewinding' the file so I can compare the stop element of one Z item with the start element of the next one. My present code is as follows. 
    open(FILE, "$input") || die "OOPS! Can't find file!\n";
    
    while(<FILE>)
    {
        @file = split(/\s+/, $_);

        $zitem = $file[0];

        if("$zitem" eq "Z")
       {
        $start_element = $file[1];
        $stop_element = $file[2];
           }
     }

[download]
Any pointers in the right direction much appreciated.

In reply to 'rewinding' file to get value from previous line in file? by Angharad

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