#!env perl
#
#   ex_sql_placeholders_via_tied_variables.pl
#
use strict;
use warnings;
use PH:  # my fake placeholders package

# Tell PH which variables are to be converted into placeholders.
tie my $c1, 'PH';
tie my $c2, 'PH';
tie my $c3, 'PH';
tie my $c4, 'PH';

my $table='a_table';

sub the_sql { "select foo from $table where x=$c2 or y in ($c3, $c4, $c1)" };

# Prepare the statement
my $X = PH::prep(\&the_sql);

# Set up some values and execute:
($c2, $c3, $c4, $c1) = ('b','3','e','f');
PH::exec($X);

# Again...
($c1, $c2, $c3, $c4) = ('m','n','o','p','q');
PH::exec($X);