my $str = join ' ', map {"$_-PAT"} 1 .. 10;
warn $str;
1 while $str =~ s/PAT/REPL/;
die $str;
__END__
1-PAT 2-PAT 3-PAT 4-PAT 5-PAT 6-PAT 7-PAT 8-PAT 9-PAT 10-PAT at - line 2.
1-REPL 2-REPL 3-REPL 4-REPL 5-REPL 6-REPL 7-REPL 8-REPL 9-REPL 10-REPL at - line 4.

##</code><code>##

my $str = 'A b and A and c and A';
warn $str;
$str =~ s/A/a/i for  1,2,3; 
die $str;
__END__
A b and A and c and A at - line 3.
a b and A and c and A at - line 5.