But detecting the first occurrence of a chain is quite another problem that can be solved by memorizing the number of occurences as value associated to the string:

perl -ne 'chomp; print "new $_\n" unless $a{$_}++'  nm_of_processed_fi
+le
[download]

-- stefp -- check out TeXmacs wiki

    open my $fh => "file" or die $!;
[download]

    open my $fh => "sort -mu file |" or die $!;
[download]

No counter needed, no check, no keeping track of the previous. Ultimate code reuse.

Abigail

For me, the whole point of perl is to be able to forget this Unix stuff by getting inside one hood. Perl is the (almost) the same on every platform. And the effort to learn perl is offset by being able to forget this myrad of Unix commands with myriad of options that are supported or not on a given platform. Also there is often overhead avoided by perl. In the case at hand, we have to fork and pipe (no big deal) and sort (this last can cost if the processed file is very big)

But again, TMTOWTDI.

-- stefp -- check out TeXmacs wiki

Is having to learn a myriad of Unix command worse than having to learn a myriad of APIs of a myriad of Perl modules? Or do you plan to do everything yourself? I rather reuse what others have done....

Note also that IEEE Std 1003.1 - 2001 (aka POSIX) "Shell and Utilities" require the -m and -u options.

As for the overhead of sort, in the given example, no sort is actually done. The -m option, for merge, merges files which are already presumed to be sorted - but when given one file, this passes things unsorted.

Abigail

Why not just use the program uniq? It would appear to perform the same function as you desire, and is perhaps more recognizable when reading.

uniq works as well; my point was more about using the toolkit available then sort vs uniq.

Abigail

Assuming you don't want to write the three lines which compare the present value to some old value, you could use:

while(<DATA>) {

  chomp;
  print "pleasure - $_\n" if ($_ ne $old) && ($old = $_);
}

__DATA__
apples
apples
apples
oranges
pears
bread
bread
[download]

--
Steve Marvell

do i need to use a counter, or say "if $foo ne $previousfoo", or is there any easier way?

open(my $fh, "somefile.txt") or die("ack - $!");
my @lines = <$fh>; # let's hope this isn't a large file ...
for (0 .. $#lines) {
    print "a change - $lines[$_]"
        if $lines[$_] ne $lines[$_ - 1];
}
[download]

_________
broquaint