1 while $str =~ s/PAT/REPL/;

Is the idiom supposed to contain the /g modifier? You didn't include it and I can't say I've ever seen 1 while s/foo/bar/, only 1 while s/foo/bar/g;. So tell me, should there be a /g there or am I in for a new lesson in the regex classroom?

There doesn't have to be a /g modifier. For some regex/string pairs, it doesn't matter whether there's a /g modifier. For others, it does.

Abigail

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.
[download]

An infinite loop with 1 while

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.
[download]

1 while $str =~ s/PAT/REPL/;

Why not just $str =~ s/PAT/REPL/g;? Gives same result...

$str =~ s/A/a/i for 1,2,3;

All this really shows is that without 1 while or the /g modifier that it always matches at the beginning again during reiteration...

I don't mean to be rude, but you didn't really demonstrate anything too revealing :) I'm looking for a case where there is a difference between 1 while s/foo/bar/ and 1 while s/foo/bar/g.