rewinding filehandle/line skipping ?

[Anonymous Monk]

hello,
I have written to a file and would like to then read from the top
of that file. How do I rewind a file to the beginning ?
Also I have a problem with a while loop...here is the code

while (<DATA2>)
{
    $line=<DATA2>;
    print $line;
    
    
    @array = split(/ /, $line);        #split the line up into array s
+o [0] is the id and [1] indel 1 etc.
    
    #print $array[0];
    #print "\n";

    foreach $indel (@array)            #look at each indel in turn
    {
    next if $indel=~/>/;            #skip the id
    
    @character = split(//, $indel);        #look a character at a time
        foreach $char (@character)
        {
            if ($char=~/-/)        
            {                #if there is a gap add 1 to $count
            $count++;
            }
            
        }
        if($go==0)                #if id hasnt been printed yet
        {    
        print DATA3 "$array[0]";
        print DATA3 "\n";
        $go++;
        }

    @letter = qw(A B C D E F G H I J K L M N O P Q R S T U V W X Y Z);
+    #converting numbers into letters A=0 etc.
    

    print DATA3 "$letter[$count]";
    $count=0;
    
    
    }
print DATA3 "\n";
    $go=0;
}

I am reading through my DATA2 file and printing to DATA3.
The problem is, for some reason the program is skipping every other line in DATA2. (I have checked DATA2 is what I expected it to be). At the print $line command only every other line is printed. Any ideas why ?

Thanks

[Molt]

To rewind a file to beginning use seek FILE,0,0. Read the seek for more info on how this works.

Update:Also spotted why you're losing data.. the while (<DATA2>) reads in one line itself into $_, and then you read in a second into $line with $line= <DATA2>, with the result that half the lines are entirely ignored. A better way would be while (my $line= <DATA2>) instead of either of both of the other lines.

[Zaxo]

The problem is, for some reason the program is skipping every other line in DATA2.

The problem is that you are reading two lines, but working on only one of them, replace

  while (<DATA2>)
  {
      $line=<DATA2>;

with:

  while ($line = <DATA2>) {

I think your code would benefit from use strict; and some lexical scoping. The pronoun $_ instead of $line might help too.

After Compline,
Zaxo

[jmcnamara]

Here is a short example of writing to a file and rewinding it for reading. Note the +> in the open:

    #!/usr/local/bin/perl -w

    use strict;

    open MYFILE, "+>somefile.txt" or die "Error message here: $!\n";

    # Write to the file
    print MYFILE "These are the days\n";
    print MYFILE "and these are the days\n";

    # Rewind the file for reading
    seek(MYFILE, 0, 0);

    while (<MYFILE>) {
        print $_;
    }

    close MYFILE;

See also perlopentut.

--
John.

[Anonymous Monk]

Thanx - that worked a treat !

[cybear]

Anonymous Monk, you could also close(file) then open(file) again.

and as for the "while loop loosing data" thing... I had that problem initially also. :-)

[cjf]

Could this be a job for Tie::File?