coreutils: The uniq command

 
 The ‘uniq’ Command
 ==================
 
 Finally (at least for now), we’ll look at the ‘uniq’ program.  When
 sorting data, you will often end up with duplicate lines, lines that are
 identical.  Usually, all you need is one instance of each line.  This is
 where ‘uniq’ comes in.  The ‘uniq’ program reads its standard input.  It
 prints only one copy of each repeated line.  It does have several
 options.  Later on, we’ll use the ‘-c’ option, which prints each unique
 line, preceded by a count of the number of times that line occurred in
 the input.