need a clearer understanding

DanielM0412 has asked for the wisdom of the Perl Monks concerning the following question:

my %hash = ();
my $line = "";
[download]

What do those two mean?? why do people do this?

Update

sub readfasta {
  my $ifn = shift;
  my $IFH;
  open($IFH, "<$ifn") or die "cannot open file $ifn\n";
  my $line;
  my %ret;
  my $tot = 0;
  while($line = <$IFH> ){
    chomp $line;
    if(not($line eq "")) { ##### why does $line equal "" ?
      my @tmp = split(//,$line);
      if($tmp[0] eq ">") {
        my $nm = substr($line,1);
        $nm = $nm . $tot;
        $tot++;
        $line = <$IFH>;
        chomp $line;
        $ret{$nm} = $line;
      }
    }
  }
  close($IFH);
  return(\%ret);
}
[download]

what does $line = ""; mean?

Comment on need a clearer understanding Select or Download Code

Replies are listed 'Best First'.
Re: need a clearer understanding by Your Mother (Archbishop) on Aug 09, 2011 at 19:02 UTC
Initializing hashes or arrays that way doesn’t buy anything. The scalar initialization to an empty string can actually matter if you want to avoid a certain kind of warning– `moo@cow[91]~>perl -we 'my $s; $s =~ /./' Use of uninitialized value $s in pattern match (m//) at -e line 1. moo@cow[92]~>perl -we 'my $s = ""; $s =~ /./' moo@cow[93]~>` [download] I prefer `no warnings "uninitialized";` for this general case but sometimes you really do want to know if the scalar has an assignment, even the empty string, or not.	[reply] [d/l] [select]
Re^2: need a clearer understanding by DanielM0412 (Acolyte) on Aug 09, 2011 at 19:06 UTC
ill update the code	[reply]
Re^3: need a clearer understanding by Your Mother (Archbishop) on Aug 10, 2011 at 02:28 UTC
Please don't update your post without leaving the original question and labeling the update. It makes the original answers seem non-sensical.	[reply]
Re: need a clearer understanding by duyet (Friar) on Aug 09, 2011 at 19:49 UTC
`chomp $line; if(not($line eq "")) { ##### why does $line equal "" ?` [download] $line can be empty after chomp. So the code between the if() doesn't get executed if line is empty.	[reply] [d/l]
Re^2: need a clearer understanding by Anonymous Monk on Aug 09, 2011 at 20:27 UTC
> So the code between the if() doesn't get executed if line is empty. I'd probably rewrite it this way to kill one indent level: `next if $line eq "";`	[reply] [d/l]
Re: need a clearer understanding by parv (Parson) on Aug 09, 2011 at 19:20 UTC
`... while($line = <$IFH> ){ chomp $line; if(not($line eq "")) { ##### why does $line equal "" ? my @tmp = split(//,$line); ...` [download] what does $line = ""; mean? If the "`#####`" comment is anything to go by, then a test for "not empty line" is being done in "`not( $line eq "" )`". In that case your question is actually different than the comment, where you assign an empty string to `$line` variable.	[reply] [d/l] [select]
Re^2: need a clearer understanding by duyet (Friar) on Aug 09, 2011 at 19:51 UTC
I think he means `($line eq "")`	[reply] [d/l]
Re: need a clearer understanding by Utilitarian (Vicar) on Aug 10, 2011 at 09:16 UTC
I suspect that your failure to put the code in your question in a code block is the reason people are finding you hard to answer. `if($tmp[0] eq ">") { my $nm = substr($line,1); $nm = $nm . $tot; $tot++; $line = <$IFH>; #IS THIS THE LINE YOU MEANT ? chomp $line; $ret{$nm} = $line; }` [download] If my guess is correct it means exactly the same as the same code in the `while ($line = <$IFH>){` line that surrounds the read. It reads the next line into the `$line` variable (If not end of file) within a block which is only run if the previous line began with a "`>`" character. `print "Good ",qw(night morning afternoon evening)[(localtime)[2]/6]," fellow monks."`	[reply] [d/l] [select]
Re: need a clearer understanding by locked_user sundialsvc4 (Abbot) on Aug 09, 2011 at 23:29 UTC
It is really difficult to know where this question is going. As you can see from `perldoc -f chomp`, this function removes any “newline” characters from the record that has just been read. The next statement looks to see if the resulting string is “entirely empty.” (Notice that it does not consider whether or not the string “consists entirely of spaces,” but that’s another story.) Beyond that, we really need more clarification and guidance from you... Help us to help you.