Perl: how to compare array to hash and print out results - perl

Question

I'm quite new to Perl, so I'm sorry if this is somewhat rudimentary.
I'm working with a Perl script that is working as a wrapper for some Python, text formatting, etc. and I'm struggling to get my desired output.
The script takes a folder, for this example, the folder contains 6 text files (test1.txt through test6.txt). The script then extracts some information from the files, runs a series of command line programs and then outputs a tab-delimited result. However, that result contains only those results that made it through the rest of the processing by the script, i.e. the result.
Here are some snippets of what I have so far:
use strict;
use warnings;
## create array to capture all of the file names from the folder
opendir(DIR, $folder) or die "couldn't open $folder: $!\n";
my #filenames = grep { /\.txt$/ } readdir DIR;
closedir DIR;
#here I run some subroutines, the last one looks like this
my $results = `blastn -query $shortname.fasta -db DB/$db -outfmt "6 qseqid sseqid score evalue" -max_target_seqs 1`;
#now I would like to compare what is in the #filenames array with $results
Example of tab delimited result - stored in $results:
test1.txt 200 1:1-20 79 80
test3.txt 800 1:1-200 900 80
test5.txt 900 1:1-700 100 2000
test6.txt 600 1:1-1000 200 70
I would like the final output to include all of the files that were run through the script, so I think I need a way to compare two arrays or perhaps compare an array to a hash?
Example of the desired output:
test1.txt 200 1:1-20 79 80
test2.txt 0 No result
test3.txt 800 1:1-200 900 80
test4.txt 0 No result
test5.txt 900 1:1-700 100 2000
test6.txt 600 1:1-1000 200 70
Update
Ok, so I got this to work with suggestions by #terdon by reading the file into a hash and then comparing. So I was trying to figure out how to do this with out writing to file and the reading the file back in - I still can't seem to get the syntax correct. Here's what I have, however it seems like I'm not able to match the array to the hash - meaning the hash must not be correct:
#!/usr/bin/env perl
use strict;
use warnings;
#create variable to mimic blast results
my $blast_results = "file1.ab1 9 350 0.0 449 418 418 403479 403042 567
file3.ab1 2 833 0.0 895 877 877 3717226 3718105 984";
#create array to mimic filename array
my #filenames = ("file1.ab1", "file2.ab1", "file3.ab1");
#header for file
my $header = "Query\tSeq_length\tTarget found\tScore (Bits)\tExpect(E-value)\tAlign-length\tIdentities\tPositives\tChr\tStart\tEnd\n";
#initialize hash
my %hash;
#split blast results into array
my #row = split(/\s+/, $blast_results);
$hash{$row[0]}=$_;
print $header;
foreach my $file (#filenames){
## If this filename has an associated entry in the hash, print it
if(defined($hash{$file})){
print "$row[0]\t$row[9]\t$row[1]:$row[7]-$row[8]\t$row[2]\t$row[3]\t$row[4]\t$row[5]\t$row[6]\t$row[1]\t$row[7]\t$row[8]\n";
}
## If not, print this.
else{
print "$file\t0\tNo Blast Results: Sequencing Rxn Failed\n";
}
}
print "-----------------------------------\n";
print "$blast_results\n"; #test what results look like
print "-----------------------------------\n";
print "$row[0]\t$row[1]\n"; #test if array is getting split correctly
print "-----------------------------------\n";
print "$filenames[2]\n"; #test if other array present
The result from this script is (the #filenames array is not matching the hash):
Query Seq_length Target found Score (Bits) Expect(E-value) Align-length Identities Positives Chr Start End
file1.ab1 0 No Blast Results: Sequencing Rxn Failed
file2.ab1 0 No Blast Results: Sequencing Rxn Failed
file3.ab1 0 No Blast Results: Sequencing Rxn Failed
-----------------------------------
file1.ab1 9 350 0.0 449 418 418 403479 403042 567
file3.ab1 2 833 0.0 895 877 877 3717226 3718105 984
-----------------------------------
file1.ab1 9
-----------------------------------
file3.ab1

Answer 1

I'm not entirely sure what you need here but the equivalent of awk's A[$1]=$0 is done using hashes in Perl. Something like:
my %hash;
## Open the output file
open(my $fh, "<","text_file");
while(<$fh>){
## remove newlines
chomp;
## split the line
my #A=split(/\s+/);
## Save this in a hash whose keys are the 1st fields and whose
## values are the associated lines.
$hash{$A[0]}=$_;
}
close($fh);
## Now, compare the file to #filenames
foreach my $file (#filenames){
## Print the file name
print "$file\t";
## If this filename has an associated entry in the hash, print it
if(defined($hash{$file})){
print "$hash{$file}\n";
}
## If not, print this.
else{
print "0\tNo result\n";
}
}