Your code, changed to print all the say text so far every time a val1 attribute with the value FOO is encountered:

#!perlenv -w

use strict;
use XML::Parser;

my $in_say = 0;
my $say = '';

my $xp = new XML::Parser(
    Handlers => {
        Start => \&start_handler,
        End   => \&end_handler,
        Char  => \&char_handler
    }
);

if ( $#ARGV < 0 ) {
    print "usage: blah <xml file>";
    exit;
}

$xp->parsefile( $ARGV[0] );

sub start_handler {
    my ( undef, $elem, %attrs ) = @_;
    if ( $elem eq 'say' ) {
        $in_say = 1;
    }
    my $val1 = $attrs{val1};
    if (defined $val1 && $val1 eq 'FOO') {
        print $say;
    }
}

sub end_handler {
    my ( undef, $elem ) = @_;
    if ( $elem eq 'say' ) {
        $in_say = 0;
    }
}

sub char_handler {
    my ( undef, $str ) = @_;
    if ($in_say) {
        $say .= $str;
    }
}
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Also changed: The global $xp is not hidden by a local (my) $xp in every handler.