reading 2 lines at a time using perl

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

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Re: reading 2 lines at a time using perl by toolic (Bishop) on Jun 26, 2012 at 16:36 UTC
Here is one way: `use warnings; use strict; while (<>) { my $line1 = $_; my $line2 = <>; # compare 1 and 2 }` [download]	[reply] [d/l]
Re: reading 2 lines at a time using perl by cavac (Prior) on Jun 26, 2012 at 16:42 UTC
Something like this, perhaps? `#!/usr/bin/env perl use strict; use warnings; my ($first, $second); while(($first = <DATA>) && ($second = <DATA>)) { print "1: $first", "2: $second\n"; if($first eq $second) { print STDERR "Duplicate line $first"; } } __DATA__ Hello World Hallo Welt Servas Woit foo foo` [download] "You have reached the Monastery. All our helpdesk monks are busy at the moment. Please press "1" to instantly donate 10 currency units for a good cause or press "2" to hang up. Or you can dial "12" to get connected directly to second level support."	[reply] [d/l]
Re: reading 2 lines at a time using perl by tobyink (Canon) on Jun 26, 2012 at 20:01 UTC
Assuming your filehandle is called `$fh`, then this is quite nice: `use strict; use Data::Dumper; my $count = 0; while (my @both = grep length, ~~<$fh>, ~~<$fh>) { chomp @both; print Dumper \@both; }` [download] It might be even nicer if the `grep length` weren't necessary, but unfortunately it is. `perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'`	[reply] [d/l] [select]
Re: reading 2 lines at a time using perl by johngg (Canon) on Jun 26, 2012 at 23:29 UTC
Another way using eof, a scalar readline and a ternary in a map. `knoppix@Microknoppix:~$ perl -Mstrict -Mwarnings -E ' > open my $fh, q{<}, \ <<EOD or die $!; > Line 1 > Line 2 > Line 3 > Line 4 > Line 5 > EOD > > while ( not eof $fh ) > { > my @two = map { eof $fh ? () : scalar <$fh> } 1 .. 2; > chomp @two; > say qq{@two}; > }' Line 1 Line 2 Line 3 Line 4 Line 5 knoppix@Microknoppix:~$` [download] Cheers, JohnGG	[reply] [d/l]