maybe there isn't a tab character in the string you are trying to split?

Have you tried debugging the code yourself at all? Something simple as a sanity check would be to:

foreach my $filename (@files) {
    ...
    
   while (<FILE>) {
      chomp;
      next unless length; #Skip blank lines

      my @params = split /\t/, $_, 2;
      
      unless (2 == @params) {
        warn "Line $. in $filename badly formed\n";
        next;
      }
      
      $insert->execute() or print $db->errstr;
   }
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It is worth thinking about how stuff could go wrong rather than how it might go right. It is also worth checking documentation for any construct you are not absolutely sure about. Getting to know your way around the documentation for whatever you are doing is generally much better in the long run than crawling cap in hand to PerlMonks every time you hit a problem. We much prefer to solve interesting problems rather then dumb ones that are more due to laziness than inexperience.

There you go making assumptions again. You are passing whatever the "split" function happens to be returning -- which would be one arg if there were no tab characters in the string being split.

After some testing i noticed that while(<FILE>) returns a line-by-line data of the file and it is storing it in $_
That's good by what i need is to get to whole data content in one var so the above solution aint gonna help me, of course i could concatenate every line after another to construct the whole data of the file but that would be dumb.
I noticed after trying every weird idea that came into my mind that $data=<FILE> would save the whole file's contents in a split of a sec without the need for looping, so what i did to make the job done was the following:

#=========== INSERTING MULTIPLE FILENAMES & CONTENTS INTO DATABASE ===
+==========

my $data;
my $insert = $db->prepare( 'INSERT INTO articles (title, body) VALUES 
+(?, ?)' );

my @files = glob "$ENV{'DOCUMENT_ROOT'}/data/text/*.txt";

foreach (@files)
{
   open FILE, "$_" or die $!;
      $_ = map m{([^/]+)\.txt}, $_;  #Strip out of the string th path 
+and extension leaving only the filename intact
      $data = <FILE>;                #Grab the whole file contents at 
+once
      $insert->execute($_, $data) or print $db->errstr;
   close FILE;
}
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All that in order to achieve opening of all files one-by-one and inserting each of the filename and its corresponding content as an entry in mysql table 'articles'

update:

After running this test script:

foreach (@files)
{
   open FILE, "$_" or die $!;
      print "$_", br() x3;

      $_ = map m{([^/]+)\.txt}, $_;  #Strip out of the string the path
+ and extension leaving only the filename intact
      print "$_", br() x3;

      $data = <FILE>;                #Grab the whole file contents at 
+once
      print "$data";
      exit;

   close FILE;
}
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i noticed 2 errors i cannot solve:

a) The '$_' doesn't hold the value of the current filename opened without paths and extension but instead it has the number of '1' in it. Its a syntax error obviously that i have made and don't know how to properly write it.

b) @data though it is correct because it contains the contents of each file when looping and contents are stored by me in utf8 when i write the text files
But although i'm not striping out the filename correctly, even if i was, i will still need to re-encode the filename to utf8 before inserting into the database because filenames are greek-iso.
i can do that as Encode::from_to($_, 'ISO-8859-7', 'utf-8') but the question is will i have to or the $insert->execute($_, $data); will do that automatic for me before inserting the values in the db?

foreach (@files)
{
   open FILE, "$_" or die $!;
      print "$_", br() x3;

      $_ = map m{([^/]+)\.txt}, $_;  #Strip out of the string the path
+ and extension leaving only the filename intact
      ...
}
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(Perverted enough to poke my eye with the Red Ryder BB gun.)

Why do you need to invoke map when m// would have been just fine? Instead of abusing $_ (and thus modifying @files), why not just assign the matched captured text to a normal variable?

As for getting 1s, from perldoc -f map ...

map BLOCK LIST

map EXPR,LIST

Evaluates the BLOCK or EXPR for each element of LIST (locally setting $_ to each element) and returns the list value composed of the results of each such evaluation. In scalar context, returns the total number of elements so generated.

Added the next day ... Or, instead of "$_ = map ..., $_", try similar to one of these ...

( my $name ) = m{ ([^/]+) \.suffix }x;

#  or,

my $name = ( m{ ([^/]+) \.suffix }x )[0];

#  or,

use File::Basename;
my $name = fileparse( $_ , qr{ \.suffix }x );
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