how to write my results to external file in perl - perl

Question

I am trying to read some particular columns from myu data into my output file, i succeed in this reading one cloumn at a time but i want to read some more columns of my interest at a time (i have list of column i want to extract in a separate tex file) because extract individual column and joining them to make one separate file will become hectic to me, here is the code i tried to extract single coulmn,
#!/usr/bin/perl
use strict;
use warnings;
open (DATA, "<file.txt") or die ("Unable to open file");
my $search_string = "IADC512444";
my $header = <DATA>;
my #header_titles = split /\t/, $header;
my $extract_col = 0;
for my $header_line (#header_titles) {
last if $header_line =~ m/$search_string/;
$extract_col++;
}
print "Extracting column $extract_col\n";
while ( my $row = <DATA> ) {
last unless $row =~ /\S/;
chomp $row;
my #cells = split /\t/, $row;
print "$cells[$extract_col] ";
}
is there any possibility to extract all columns at a time instead of only IADC512444 i want from my textfile into outfile on to my harddisc? please help me in solving this problem,
Thanks

Answer 1

If you need to print the contents to a file on disk then you should open a file in write mode and write to it. Also if you want more columns you can do that by accessing corresponding element in the array cells. In this example i am printing the column you are printing plus column 1 and 2
open(OUT_FILE,">path_to_out_file") || die "cant open file...";
while ( my $row = <DATA> ) {
last unless $row =~ /\S/;
chomp $row;
my #cells = split /\t/, $row;
#print "$cells[$extract_col] ";
print OUT_FILE "$cells[$extract_col],$cells[1],$cells[2]\n";
}
close(OUT_FILE)
I have tweaked the code little bit to suit your requirement.
In the variable req_hdr_string you should say the column names which you require separated by ,
So it will be splitted and stored in a hash.
Then from the header i get the position of the column and print only those
#!/usr/bin/perl
use strict;
use warnings;
open (DATA, "<h11.txt") or die ("Unable to open file");
my $req_hdr_string = "abc,ghi,mno,";
my %req_hdrs = ();
my %extract_col = ();
foreach(split /,/, $req_hdr_string)
{
print "req hdr is:$_\n";
$req_hdrs{$_} = $_;
}
my $index = 0;
my $header = <DATA>;
chomp $header;
foreach (split /\t/, $header)
{
print "input is:|$_|\n";
if(exists $req_hdrs{$_})
{
print "\treq index is:$index\n";
$extract_col{$index} = 1;
}
$index++;
}
open(OUT_FILE,">out_file") || die "cant open file...";
while ( my $row = <DATA> )
{
last unless $row =~ /\S/;
chomp $row;
my #cells = split /\t/, $row;
foreach $index (sort keys%extract_col)
{
print OUT_FILE "$cells[$index],";
}
print OUT_FILE "\n";
}
close(OUT_FILE);
close(DATA);