Here's another option:

use strict;
use warnings;

local $/ = "//\n";

while (<>) {
    chomp;
    my ( $len, $id, $parts ) = /(\d+)\s+(.+?)\n(.+)/s;
    $parts =~ s/\n//g;
    $parts =~ /.{$len}/p;
    print ">$id\n${^MATCH}\n${^POSTMATCH}\n"
}

[download]

If you're using Perl v5.14+, you can combine the substitution and matching into a single line as follows:

$parts =~ s/\n//gr =~ /.{$len}/p;

Hope this helps!

In reply to Re: create an one-line format for this by Kenosis
in thread create an one-line format for this by Anonymous Monk

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