<?php
$date = "20210321";
validateDateFormat($date);
$date = "202103213333";
validateDateFormat($date);
$date = "20210";
validateDateFormat($date);
$date = "2010aass";
validateDateFormat($date);
$date = "20101333";
validateDateFormat($date); 
function validateDateFormat($date)
{
    // 右0埋め
    $_date = str_pad($date, 8, 0, STR_PAD_RIGHT);
    // 8桁以上の場合は切り詰め
    $_date =substr($_date, 0,8);
    print($_date)."\n";
    // checkdate の引数は int
    $year = intval(substr($_date, 0,4)); 
    var_dump($year);
    $month = intval(substr($_date,4,2));
    var_dump($month);
    $day = intval(substr($_date, 6,2)); 
    var_dump($day);
    if(checkdate($month, $day, $year) === false)
    {
        echo 'NG : 日付が正しくありません。'."\n";
    }
    else
    {
        echo 'OK！'."\n";
    }
}

https://metacpan.org/release/TURNSTEP/DBD-Pg-3.15.0/source/README

https://base64.work/so/perl/3606027

# DBI_DSN                     dbi:Pg:db="postgres";port=5440;host=localhost/dbdpg_test_database/data/socket
# DBI_USER                    jgp
#DBI_USER=<username>
#DBI_PASS=<password>

cpan YAML
cpan Test::Simple
cpan DBD::Pg

export POSTGRES_HOME=/var/lib/pgsql/13
export PATH=$PATH:/usr/pgsql-13/bin
export DBI_DSN='dbi:Pg:db="postgres";port=5432;host=localhost'
export DBI_DSN='dbi:Pg:dbname=testdb;;port=5432;'
export DBI_USER='postgres'
export DBI_PASS='postgres'