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Re: printing every 2nd entry in a list backwards

by Discipulus (Monsignor)
on May 19, 2017 at 12:31 UTC ( #1190604=note: print w/replies, xml ) Need Help??


in reply to printing every 2nd entry in a list backwards

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If i have understood the question you can:

UPDATE: ok i have misunderstood.. what i'm doing there is: given a file and a sequence of numbers, for this file print the reverse line order skipping even entries.

use strict; use warnings; # shift the file from args my $file_path = shift @ARGV; # a simple switch my $sw = 1; # take indices in reverse order and skipping 2th 4th.. my @wanted_lines = grep {$sw++ and $sw % 2 == 0} reverse @ARGV; open my $fh, '<', $file_path or die "unable to open $file_path! $!"; # in list context eat all the file at once my @all_lines = <$fh>; # of those all lines print a slice: the slice is @wanted_lines # with all valuse lowered by one because indices of array start at 0 # lines starts a 1 print for @all_lines[map{$_-1}@wanted_lines]; # invoke like: # inverted_alternated.pl file_to_read.txt 1 2 3 4

L*

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