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

Good Morning Esteemed Monks!

My question has to do with auto increments and I think I am missing something very simple as when I add rows to my file the ID should go up by 1 when each new entry is added correct? Please refer to my code below and point me in the right direction as to what I am missing. Thanks in advance! 



my $id = 1;

my $output="data.txt";
open(DAT,">>$output") || die("Cannot Open File");

print DAT ($id++);
print DAT (":");
print DAT ($name);
print DAT (":");
print DAT ($number);
print DAT (":");
print DAT ($address);
print DAT (":");
print DAT ($phone);
print DAT (":");
print DAT ($email);
print DAT ("\n");

close (DAT);

[download]

Replies are listed 'Best First'.
Re: auto increment
by choroba (Cardinal) on May 05, 2015 at 13:08 UTC
    You only increment $id once. Before incrementing it, you set it to 1. If you want to add an entry to a file, you have first to read the last entry from the file, get its id, increment it, and then write the new entry.
    لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ
[reply]

      Exactly. Like this, for example:

      use feature 'say';

my $output = "data.txt";
open(DAT, '+<', $output) || die("Cannot Open File");
my $id;
while (<DAT>) {
    ($id) = m/\A(\d+):/;
}

say DAT join ':', ++$id, $name, $number, $address, $phone, $email;

close(DAT);

      [download]
[reply]
[d/l]

        Better yet:

        use feature 'say';

my $output = "data.txt";
open(DAT, '+<', $output) || die("Cannot Open File");

my $line;
$line = <DAT> until eof DAT;
my ($id) = $line =~ m/\A(\d+):/;

say DAT join ':', ++$id, $name, $number, $address, $phone, $email;

close(DAT);

        [download]

        This way, the regular expression is only executed once - on the last line.

        Sorry for the double post, I can't edit my comments (not enough powers yet).

[reply]
[d/l]
Re: auto increment
by pme (Monsignor) on May 05, 2015 at 13:30 UTC
    You can read the whole file into the memory (@file) and take the id from the very last line. 
    open(DAT, "<$output") || die("Cannot Open File");
my @file = <DAT>;
close DAT;
my $id = (split(':', $file[-1]))[0];
$id++;
print "$id\n";

    [download]
[reply]
[d/l]
Re: auto increment
by edimusrex (Monk) on May 05, 2015 at 14:39 UTC
    I would set the ID number equal to the line number + 1 by reading the file into an array first. Something like this would do the trick. Each to you executed the script the ID should increment by 1.

    my $file = "data.txt";
open FILE, "<$file";
@lines = <FILE>;
close FILE;

$id = @lines;
$id++;

open DAT, ">>$file";
print DAT ("${id}:${name}:${number}:${address}:${phone}:${email}\n");
close DAT;

    [download]
[reply]
[d/l]
      You don't need to store all the lines to count them. You can just count them when reading them: 
      my $count = 0;
$count++ while <FILE>;

      [download]

      In fact, Perl already does that. 

      1 while <FILE>;
my $count = $.;

      [download]
      لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ
[reply]
[d/l]
[select]
        Ah, that's a nice tip. Thanks
[reply]

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