I am trying to learn source filter basics, after reading some documentation and trying out small examples. I wanted to work with some bigger ones. I find the given statement a lot more useful than the if-else structure. But the substitution isn't working inside the given structure.

The filter.

package filtertest;

use Filter::Util::Call;

use strict;
use warnings;
use feature "switch";


sub import {
    my $self = @_;
    my $ref = [];
    filter_add( bless $ref );
}

sub filter {
    my $self = @_;
    my $status;
    $status = filter_read();

    die "some thing messed up" if $status < 0 ;
    die "EOF reached" if $status == 0;
 

    given( $_ ){

        when (/^say*/) { 
            print "\n%%reaching here as $_ was matched%%";
            s/say/print/;
            print "\n%%It was changed to $_%%";
        }
  
        when ( /^use/ ) {
            print "\n&&reaching here as $_ was matched&&";
        }

        default { 
            print "\n**default condition**"
        }
 
    }

    $status;
}

1;
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The code I'm trying to run.

use strict;
use warnings;

use filtertest;


say 'hello.world';


say 'hello';
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The output is.

**default condition**
**default condition**
%%reaching here as say 'hello.world';
 was matched%%
%%It was changed to print 'hello.world';
String found where operator expected at filter_test.pl line 9, near "s
+ay 'hello.world'"
    (Do you need to predeclare say?)
%%
**default condition**
**default condition**
%%reaching here as say 'hello';
 was matched%%
%%It was changed to print 'hello';
String found where operator expected at filter_test.pl line 12, near "
+say 'hello'"
    (Do you need to predeclare say?)
syntax error at filter_test.pl line 9, near "say 'hello.world'"
EOF reached at filtertest.pm line 24.
%%
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What could be possibly going wrong?