Perl: comparing words in two files - perl

Question

This is my current script to try and compare the words in file_all.txt to the ones in file2.txt. It should print out any of the words in file_all that are not in file2.
I need to format these as one word per line, but that's not the more pressing issue.
I am new to Perl ... I get C and Python more but this is being a bit tricky, I know my variable assignment is off.
use strict;
use warnings;
my $file2 = "file_all.txt"; %I know my assignment here is wrong
my $file1 = "file2.txt";
open my $file2, '<', 'file2' or die "Couldn't open file2: $!";
while ( my $line = <$file2> ) {
++$file2{$line};
}
open my $file1, '<', 'file1' or die "Couldn't open file1: $!";
while ( my $line = <$file1> ) {
print $line unless $file2{$line};
}
EDIT: OH, it should ignore case... like Pie is the same as PIE when comparing. and remove apostrophes
These are the errors I am getting:
"my" variable $file2 masks earlier declaration in same scope at absent.pl line 9.
"my" variable $file1 masks earlier declaration in same scope at absent.pl line 14.
Global symbol "%file2" requires explicit package name at absent.pl line 11.
Global symbol "%file2" requires explicit package name at absent.pl line 16.
Execution of absent.pl aborted due to compilation errors.

Answer 1

Your error messages:
"my" variable $file2 masks earlier declaration in same scope at absent.pl line 9.
"my" variable $file1 masks earlier declaration in same scope at absent.pl line 14.
Global symbol "%file2" requires explicit package name at absent.pl line 11.
Global symbol "%file2" requires explicit package name at absent.pl line 16.
Execution of absent.pl aborted due to compilation errors.
You are assigning a file name to $file2, and then later you are using open my $file2 ... The use of my $file2 in the second case masks the use in the first case. Then, in the body of the while loop, you pretend there is a hash table %file2, but you haven't declared it at all.
You should use more descriptive variable names to avoid conceptual confusion.
For example:
my #filenames = qw(file_all.txt file2.txt);
Using variables with integer suffixes is a code smell.
Then, factor common tasks to subroutines. In this case, what you need are: 1) A function that takes a filename and returns a table of words in that file, and 2) A function that takes a filename, and a lookup table, and prints words that are in the file, but do not appear in the lookup table.
#!/usr/bin/env perl
use strict;
use warnings;
use Carp qw( croak );
my #filenames = qw(file_all.txt file2.txt);
print "$_\n" for #{ words_notseen(
$filenames[0],
words_from_file($filenames[1])
)};
sub words_from_file {
my $filename = shift;
my %words;
open my $fh, '<', $filename
or croak "Cannot open '$filename': $!";
while (my $line = <$fh>) {
$words{ lc $_ } = 1 for split ' ', $line;
}
close $fh
or croak "Failed to close '$filename': $!";
return \%words;
}
sub words_notseen {
my $filename = shift;
my $lookup = shift;
my %words;
open my $fh, '<', $filename
or croak "Cannot open '$filename': $!";
while (my $line = <$fh>) {
for my $word (split ' ', $line) {
unless (exists $lookup->{$word}) {
$words{ $word } = 1;
}
}
}
return [ keys %words ];
}

Answer 2

You are almost there.
The % sigil denotes a hash. You can't store a file name in a hash, you need a scalar for that.
my $file2 = 'file_all.txt';
my $file1 = 'file2.txt';
You need a hash to count the occurrences.
my %count;
To open a file, specify its name - it's stored in the scalar, do you remember?
open my $FH, '<', $file2 or die "Can't open $file2: $!";
Then, process the file line by line:
while (my $line = <$FH> ) {
chomp; # Remove newline if present.
++$count{lc $line}; # Store the lowercased string.
}
Then, open the second file, process it line by line, use lc again to get the lowercased string.
To remove apostophes, use a substitution:
$line =~ s/'//g; # Replace ' by nothing globally (i.e. everywhere).

Answer 3

As you have mention in your question: It should print out any of the words in file_all that are not in file2
This below small code does this:
#!/usr/bin/perl
use strict;
use warnings;
my ($file1, $file2) = qw(file_all.txt file2.txt);
open my $fh1, '<', $file1 or die "Can't open $file1: $!";
open my $fh2, '<', $file2 or die "Can't open $file2: $!";
while (<$fh1>)
{
last if eof($fh2);
my $compline = <$fh2>;
chomp($_, $compline);
if ($_ ne $compline)
{
print "$_\n";
}
}
file_all.txt:
ab
cd
ee
ef
gh
df
file2.txt:
zz
yy
ee
ef
pp
df
Output:
ab
cd
gh

Answer 4

The issue is the following two lines:
my %file2 = "file_all.txt";
my %file1 = "file2.txt";
Here you are assigning a single value, called a SCALAR in Perl, to a Hash (denoted by the % sigil). Hashes consist of key value pairs separated by the arrow operator (=>). e.g.
my %hash = ( key => 'value' );
Hashes expect an even number of arguments because they must be given both a key and a value. You currently only give each Hash a single value, thus this error is thrown.
To assign a value to a SCALAR, you use the $ sigil:
my $file2 = "file_all.txt";
my $file1 = "file2.txt";