extract multiples columns from txt file perl

Question

I have a txt file like this:

#Genera columnA columnB columnC columnD columnN
x1       1       3       7      0.9      2
x2       5       3       13     7            


        

Answer 1

You can simplify like this and using hash slices.

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

my @wanted = ( '#Genera' , qw (  columnA columnC columnN ));

open my $input, '<', "file.txt" or die $!;

chomp ( my @header = split ' ', <$input> ); 

print join "\t", @wanted, "\n";
while ( <$input> ) { 
   my %row;
   @row{@header} = split; 
   print join "\t", @row{@wanted}, "\n";
}

Which outputs:

#Genera columnA columnC columnN 
x1  1   7   2   
x2  5   13  5   
x3  0.1 7   0.4 

If you want to exactly match your indentation then add sprintf to the mix:

E.g.:

print join "\t", map { sprintf "%8s", $_} @wanted, "\n";
while ( <$input> ) { 
   my %row;
   @row{@header} = split; 
   print join "\t", map { sprintf "%8s", $_} @row{@wanted}, "\n";
}

Which then gives:

 #Genera     columnA     columnC     columnN           
      x1           1           7           2           
      x2           5          13           5           
      x3         0.1           7         0.4