while (<fh>) { ... }
while (defined ($_ = <fh>)) { ... }

##</code><code>##

while ($var = <fh>) { ... }

##</code><code>##

if ($line =~ m/$stag/ .. /$etag/)

##</code><code>##

if (($line =~ m/$stag/) .. ($line =~ m/$etag/))

##</code><code>##

if (($line =~ m/$stag/) .. ($_ =~ m/$etag/))