japhy — Thu, 23 Mar 2000 14:33:00 +0000

Writing to the beginning of a file is extremely inefficient. You end up the following, and you probably forget to flock() the file.

code:

use Fcntl ':flock';  # for LOCK_EX

open FILE, "+<$file" or die "can't open $file for read/write: $!";
flock FILE, LOCK_EX;

if ($slurp_into_nasty_array) {
  @file = <FILE>;
  unshift @file, @new;
  seek FILE, 0, 0;
  print FILE @file;
}
elsif ($slurp_into_scalar) {
  # can also be nasty, for big files
  local $/;
  $file = <FILE>;
  seek FILE, 0, 0;
  print FILE @new, $file;
}
elsif ($while_loop) {
  push @file, $_ while <FILE>;
  seek FILE, 0, 0;
  print FILE @new, @file;
}
truncate FILE, tell FILE;  # for safety...
close FILE;
[/code]

But I seriously don't suggest you do this.  You should answer the question "why do I need to write to the top of a file?"  You can probably get around your problem by appending to the file, and reading the file's contents, but in reverse:

code:use Fcntl ':flock';
open FILE, ">>$file" or die "can't append to $file: $!";
print FILE @new;
close FILE;

open FILE, $file or die "can't read $file: $!";
unshift @lines, $_ while <FILE>;
close FILE;

# @lines is now the lines of $file in the REVERSE order (most recent addition first)
[/code]

Look into this method.  You'll be happier.

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Orpheus — Tue, 21 Mar 2000 21:39:00 +0000

Sorry I didn't get back to you sooner with that, I was at school when I posted.

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Justin S — Tue, 21 Mar 2000 20:15:00 +0000

Darn, the people who help in this forum are excellent. Thanks alot for both or your help. I'll try it out and see if it works.

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Rob Pengelly — Tue, 21 Mar 2000 20:04:00 +0000

Somthing like this will work

code:

$file = "file.txt";

open(IN,"$file.txt") or die "Cannot open $file: $!";
@data=<IN>;
close(IN);

#Now each line is an element in the array @data

$newinput = "rob\n";
unshift @data, $newinput;

#now $newinput is @data[0]

open(IN,">$file")or die "Cannot open $file: $!";
print IN @data;
close(IN);
[/code]

This will open the file, put the current data in it into an array.  Than use the unshift function to add the new input (in this case, $newinput) into the @data array as the first element.  When printed back into the file, the $newinput will be first.

Hope that helps at all.

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Justin S — Tue, 21 Mar 2000 18:22:00 +0000

No, it's not going to be in an array. It will probably use the push() command. I looked up the push() command in Programming Perl, and it gave a really vague example:

code:

for(;  {
push @ARRAY, shift @ARRAY;
...
}[/code]

Does anyone have a snippet of code for what I want to do?

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[This message has been edited by Justin Stayton (edited 21 March 2000).]

Orpheus — Tue, 21 Mar 2000 18:12:00 +0000

$array[0] will print the top line of the file if your reading it from an array.

If you wnt to move the rest of the file down you need to use the push() command.