Re: popping or shifting a line off a file

If you don't have to select the lines randomly then you could do something like this:

    #!/usr/bin/perl -w

    use strict;

    my $passwords = 'passwords';
    my $rec_size  = 9;
    my $password;

    open PASS, "+<$passwords" or die "Error message here $!";

    # Seek from end of file
    seek PASS, -$rec_size, 2;

    # Store the position of the last seek
    my $last = tell PASS;

    # Read the password but not the newline
    read PASS, $password, $rec_size -1;

    # Remove the record just read
    truncate PASS, $last;

    close PASS;

    print $password, "\n";

    __END__
[download]

This method will be significantly faster than the method shown above.

--
John.

Comment on Re: popping or shifting a line off a file Download Code

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Re: Re: popping or shifting a line off a file by nmerriweather (Friar) on Jul 29, 2002 at 20:36 UTC
i finally ended up with something similar... print &popline("passcodes.txt",10,7); sub popline { my ($file, $lineswanted, $linelength) = @_; open DATA, "+< $file"; my @fileinfo = stat DATA; my %records = (); $records{filesize} = $fileinfo[7]; $records{wanted_bytes} = $lineswanted * $linelength; $records{readpoint} = $records{filesize} - $records{wanted_byt +es}; # seek (DATA, -$records{wanted_bytes},2); # reads from the end + of file, readpoint computation not necessary seek (DATA, $records{readpoint},0); # reads from beginn +ing, used b/c readpoint computation needed for truncate my @lines = <DATA>; truncate(DATA,$records{readpoint}); return @lines; } [download] i'll add in flocking etc tonight. short of filling up a database w/20k possible keys + status tags, what i did was create a flat.txt of possible keys. this function is for 'activating' a key -- 50-100 will be pulled off the file, inserted into a db with a status flag (active/used), and merged w/documentation is this the most secure method? probably not. but if someone is going to hack my machine and grab the file -- well, i'm just going to assume that they're talented enough to hack into mysql and alter the db as they see fit.	[reply] [d/l]

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Re: Re: popping or shifting a line off a file
by nmerriweather (Friar) on Jul 29, 2002 at 20:36 UTC

print &popline("passcodes.txt",10,7);
sub popline {
    my ($file, $lineswanted, $linelength) = @_;

    open     DATA, "+< $file";
    my @fileinfo = stat DATA;
    my %records = ();
        $records{filesize} = $fileinfo[7];
        $records{wanted_bytes} = $lineswanted * $linelength;
        $records{readpoint} = $records{filesize} - $records{wanted_byt
+es};

    # seek (DATA, -$records{wanted_bytes},2);     # reads from the end
+ of file, readpoint computation not necessary
    seek (DATA, $records{readpoint},0);            # reads from beginn
+ing, used b/c readpoint computation needed for truncate

    my @lines = <DATA>;
    truncate(DATA,$records{readpoint});
    
    return @lines;
}
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