Even and uneven numbers as RegEx

New Novice has asked for the wisdom of the Perl Monks concerning the following question:

Dear Perlmonks,

I have a file (using new line as a delimiter) that is at the moment storing each kind of information twice. Naturally, I would like to get rid of all duplicates. They come in bundles, so I was thinking of just reading out every second line using a loop and storing this in a new file.

My questions:

1. Is there a regular expression for "even number"/"uneven number"?

2. What is the code for "end of file"?

3. Is there a module that could do it (although I prefer to keep things simple)?

Thanks!

Comment on Even and uneven numbers as RegEx

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Re: Even and uneven numbers as RegEx by broquaint (Abbot) on Sep 27, 2004 at 11:30 UTC
A one-line solution would be `perl -i.bak -ne 'print if $. & 1' filename` [download] That will remove all even numbered lines in the file. HTH `_________ broquaint`	[reply] [d/l]
Re: Even and uneven numbers as RegEx by grinder (Bishop) on Sep 27, 2004 at 12:26 UTC
Yes, `$num =~ /[02468]$/` (...with the proviso that some may consider that 0 (zero) is neither odd nor even). Yes, the function eof tells you if you are at the end of a file. In practise, you never need to use it, you simply keep on reading until you fall off the end. No, but if you are running on a Unix variant you should have the `uniq` command at your disposal, and it will probably run much faster than the Perl one-liners mentioned elsewhere in this thread. Using uniq has another advantage: if on occasion a line is not followed by a duplicate, it will emit both lines. The modulo-2 approach, on the other hand, will get out of sync and begin throwing away good data. - another intruder with the mooring of the heat of the Perl	[reply] [d/l]
Re: Even and uneven numbers as RegEx by zejames (Hermit) on Sep 27, 2004 at 11:31 UTC
I would do this : `my $i; while (<DATA) { print if ($i++ % 2); } __DATA__ 435 435 f,sdlf,dsl f,sdlf,dsl 64{# 64{# Blah Blah` [download] or, for a one liner : `perl -i -ne 'print if ($i++ % 2)' filename` [download] Here `$i % 2` is a mean to know if `$i` is even or not. HTH -- zejames	[reply] [d/l] [select]
Re^2: Even and uneven numbers as RegEx by davorg (Chancellor) on Sep 27, 2004 at 11:43 UTC
Why bother with your own $i variable when Perl gives you $. for free? `perl -i -ne 'print if $. % 2' filename` [download] (which is, of course, pretty much what broquaint had above) -- <http://www.dave.org.uk> "The first rule of Perl club is you do not talk about Perl club." -- Chip Salzenberg	[reply] [d/l]