Sums the numbers in the first column of a file. The utility value of this is *low* but the code is pretty and sort of symmetrical. 
    # Sum the numbers in the first column of a file

    perl -lpe '$,+=$_}{$_=+$,' file


    # Count (badly) the number of blocks allocated in a directory

    ls -ls | perl -lpe '$,+=$_}{$_=+$,'

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