map { $val .= sprintf("%02x",$_) } unpack "CCCCCC", $octetstr;
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Nice example for map in void context. I wouldn't transform that into a full foreach loop, but use a statement modifier instead

$val .= sprintf("%02x",$_) for unpack "CCCCCC", $octetstr;
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for the same reasons I wrote down elsewhere.

But then - regarding map in void context - all perl statements are executed for their side effect, and the computed value is discarded:

# result from map is discarded
# side effect: $val is populated
map { $val .= sprintf("%02x",$_) } unpack "CCCCCC", $octetstr;

# result from print is discarded (1 if successful)
# side effect: text appears on STDOUT or selected filehandle
print "hello, world!\n";

# result from assignment is 42, again discarded
# side effect: $value is populated
$value = 42;

# result from die is discarded (if any), print not done
# side effect: well...
print die;
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