Actually Tanktalus, that won't work. You said, If they don't match, print out the last match, and then reset. But when you print $line instead of $oldline, you're printing the next unique line you've found, not the line you've been counting for. Here's the altered code, also fixed so that it now runs under use strict: 
#!/usr/bin/perl
# uniq.pl: remove repeated lines.

use strict;
use diagnostics;

my $oldline = <>; # Priming read
my $n = 1;

while (my $line = <>) {
  if ($line eq $oldline) {
    $n++; #$n = $n + 1;    
  } else {
    print " $n $oldline";
    $n = 1;
    $oldline = $line;
  }
}
if ($oldline)
{
  print " $n $oldline";
}

[download]
Note: The program will hang if there isn't at least one line of data to read.

In reply to Re^4: counting lines in perl by crashtest
in thread counting lines in perl by imhotep

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