Dear Monks,
I am looking for a “true once” Boolean value, to test within a loop. I need something that will give me a TRUE value the first time, and FALSE the remaining times or vice-versa. I know that this need is shared by somebody else (Re: Being Popular) and I wonder if somebody has any idioms to offer.
Here is a practical example. I need to create a MySQL INSERT statement, exploiting the special syntax to have multiple values within the same instruction. 
INSERT INTO tablename VALUES 
(value1, value2, value3), 
(value1, value2, value3),
(value1,value2, value3);

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To create such statement, I am parsing the raw data from an input file, and I have the problem of inserting commas after each set of values, except the last one (or we could say before each set, except the first one).
I came up with two solutions. The first one has a TRUE scalar that becomes FALSE upon being called: 
my $should_print = 1;
while (...) {
    print "'\n" if ($should_print? --$should_print : 1);
    # munging ...
}

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A little tricky, but it works. The first call will change the TRUE value to a FALSE one, thus preventing the print from happening. Each successive call will return 1 (TRUE) with the help of the ternary operator, unleashing the print.
The second solution will get over the TRUE-once need by means of grep and map, and although the result is exactly the same, it looks like something that I should send to an Obfuscated Code Contest.
(Thinking again, though, also the first solution, where a Boolean test returns the opposite of a scalar value, would be a good candidate for an OCC.)
The following program illustrates the two solutions. I would be glad to find out if there is anything easier to read or to implement.
Personally, I like the while loop, but I am keeping an open mind on alternatives. Any hints?
Thanks
gmax

#!/usr/bin/perl -w

use strict;

print <<MYSQL;
CREATE DATABASE IF NOT EXISTS chess;
USE chess;
DROP TABLE IF EXISTS eco_class;
# create table statement
CREATE TABLE eco_class (
    eco_id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
    eco CHAR(3) NOT NULL,
    opening VARCHAR(50) NOT NULL,
    variation VARCHAR(50),
    moves VARCHAR(200) NOT NULL,
    KEY eco(eco), KEY opening(opening),
    KEY variation (variation), KEY moves(moves));
# create the header for the insert statement
INSERT INTO eco_class VALUES 
MYSQL

my @line;    # input fields
my $should_print =1;    # flag for first line

with_while(); # comment to test the alternative
#with_map();  # uncomment to test the alternative 
print ";\n";

sub with_while {
    while (<DATA>) {
        chomp;            # removes trailing newline
        next if /^\s*$/;    # skips blank lines
        # skips the first line
        print ",\n" if ($should_print? --$should_print : 1); 
        @line = split /;/;    # gets individual records
        print "(NULL, ", quotrim($line[0]), 
            ", ", quotrim($line[1]), ", "; 
        # the third field may be missing
        print scalar @line < 4 ? 
            "NULL, " . quotrim($line[2]) 
            : quotrim($line[2]) . ", " . quotrim($line[3]), ")";
        }
}

sub with_map {
    print join ",\n" , grep { defined $_ } map { 
        chomp;            # removes trailing newline
        if (/^\s*$/ ) {        # skips blank lines
            $_ = undef;
        }
        else {
            @line = split /;/;    # gets individual records
            $_ =  "(NULL, " 
              . quotrim($line[0]) 
              .  ", " . quotrim($line[1]) 
              . ", ";
            $_ .= scalar @line < 4 ? 
               "NULL, " . quotrim($line[2]) 
               : quotrim($line[2]) . ", " 
                 . quotrim($line[3]), ")";
            $_ .= ")";
        }
    } <DATA>;
}

sub quotrim { # quote and trim :->
    $_[0] =~ s/\"/\\"/g;
       $_[0] =~ s/^\s+//;
       $_[0] =~ s/\s+$//;
    return '"' . $_[0] . '"';
}

#sample data follows
__DATA__

A00;Polish (Sokolsky) opening;1.b4
A00;Polish;Tuebingen Variation ;1.b4 Nh6
A00;Polish;Outflank Variation ;1.b4 c6
A00;Benko's Opening;1.g3
A00;Lasker simul special;1.g3 h5
A00;Benko's Opening;reversed Alekhine;1.g3 e5 2.Nf3
A00;Grob's attack;1.g4
A00;Grob;Spike attack;1.g4 d5 2.Bg2 c6 3.g5
A00;Grob;Fritz gambit;1.g4 d5 2.Bg2 Bxg4 3.c4
A00;Grob;Romford counter-gambit;1.g4 d5 2.Bg2 Bxg4 3.c4 d4
A00;Clemenz (Mead's, Basman's or de Klerk's) Opening;1.h3
A00;Global Opening;1.h3 e5 2.a3
A00;Amar (Paris) Opening;1.Nh3
A00;Amar gambit;1.Nh3 d5 2.g3 e5 3.f4 Bxh3 4.Bxh3 exf4

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In reply to A TRUE-once variable by gmax

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