$ perl -wle '"a" =~ /a/; // and print for qw( a b a b a b )'
a
a
a

##</code><code>##

$ perl -le 'print for a .. z' | perl  -nle 'if (/d/ .. /h/) { print unless // }'
e
f
g

##</code><code>##

$ perl -le 'print for a .. z' | perl  -nle 'if (/d/ .. /h/) { next unless //; print }'
d
f
g
h

##</code><code>##

...
Matching REx "d" against "d"
Intuit: trying to determine minimum start position...
  doing 'check' fbm scan, [0..1] gave 0
  Found anchored substr "d" at offset 0 (rx_origin now 0)...
  (multiline anchor test skipped)
Intuit: Successfully guessed: match at offset 0
Matching REx "h" against "d"
Intuit: trying to determine minimum start position...
  doing 'check' fbm scan, [0..1] gave -1
  Did not find anchored substr "h"...
Match rejected by optimizer
Matching REx "d" against "d"
Intuit: trying to determine minimum start position...
  doing 'check' fbm scan, [0..1] gave 0
  Found anchored substr "d" at offset 0 (rx_origin now 0)...
  (multiline anchor test skipped)
Intuit: Successfully guessed: match at offset 0
Matching REx "h" against "e"
Intuit: trying to determine minimum start position...
  doing 'check' fbm scan, [0..1] gave -1
  Did not find anchored substr "h"...
Match rejected by optimizer
Matching REx "d" against "e"
Intuit: trying to determine minimum start position...
  doing 'check' fbm scan, [0..1] gave -1
  Did not find anchored substr "d"...
Match rejected by optimizer
Matching REx "h" against "f"
Intuit: trying to determine minimum start position...
  doing 'check' fbm scan, [0..1] gave -1
  Did not find anchored substr "h"...
Match rejected by optimizer
Matching REx "" against "f"                      (*)
   0 <> <f>                  |   0| 1:NOTHING(2)
   0 <> <f>                  |   0| 2:END(0)
Match successful!
...

##</code><code>##

$ perl -le 'print for a .. z' | perl  -ne 'if (/d/ .. /h/) { next unless //; print }} continue {'
d
e
f
g
h