using perl, how to select last 2 lines in the case of each row has same word?

Question

Bini  --  -21.89753  -20.47853  -20.27835  -18.34952  -16.23454

Bini  --  -16.89753  -14.47853  -13.27835  -12.34952  -11.23454

Bini  --  -10.09014  

Answer 1

••• NOTE •••• The input file here is specific to your more recent, blocked, question (using perl, how to select last 2 lines in the case of each row has same word?(re-questioned..)) and as such will only work with that input.

This is the input you recently provided:

Bini  --  -10.09014  

cidi

Bini  --  -21.89753  -21.47853  -20.27835  -20.34952  -17.23454

Bini  --  -16.89753  -12.47853  -11.27835  -11.34952  -10.23454

Bini  --  -09.09014  

light is 3.4

This will achieve exactly what you want (i.e. extract the last two elements from the second-to-last line starting with 'Bini' and the last element from the last line ending in 'Bini') , but no more ...

#!/usr/bin/perl
use warnings;
use strict;

my $file = 'location/of/your/file.txt';
open my $input, '<', $file or die "Can't write to $file: $!";

my $line = 0;
my (@element1, @element2, @element3);
while (<$input>){ 
    chomp;
    next if ($_ =~ /^\s*$/); # skips a line of input if the line is blank
        if ($_ =~ /^Bini/) { # if the line starts with Bini
            $line++; # Add 1 to count variable
            my @split = split('\s+'); # split by spaces
            if ($line == 3) { # if the line number = 3 (i.e. second to last)
                push @element1, $split[-1]; # add the last element of split (-10.234...) to @element1
                push @element2, $split[-2]; # # add the second-to-last element of split to @element2
            }
            elsif ($line == 4) { # if the line number is 4 (last line starting with Bini
                push @element3, $split[-1]; # # add the last element of split to @element1
            }
        }
}

print "$element3[0]\t$element1[0]\t$element2[0]\n";

Output:

-09.09014   -10.23454   -11.34952

Answer 2

You can take all numbers from every line, push them at the end of @entries, and always keep only last three.

my @entries;
while(my $line = <FILE>) {
     next if $line !~ /Bini/;
     push @entries, grep /\d/, split /\s+/,$line;
     @entries = @entries[-3 .. -1] if @entries > 3;
}
print join "\n", @entries;

output

-12.34952
-11.23454
-10.09014