unpack()访问子串

The unpack function gives only read access, but is faster when you have many substrings to extract.

# get a 5-byte string, skip 3 bytes,

# then grab two 8-byte strings, then the rest;

 # (NB: only works on ASCII data, not Unicode)

($leading, $s1, $s2, $trailing) = unpack("A5 x3 A8 A8 A*", $data);

 # split at 5-byte boundaries

@fivers = unpack("A5" x (length($string)/5), $string);

# chop string into individual single-byte characters

@chars = unpack("A1" x length($string), $string);

$string = "good good start, day day up!";
($word1, $word2,$word3)=unpack("A5 x5 A5 A*",$string);
print $word1."+".$word2."+".$word3;
print "\n";

@fivers = unpack("A5" x (length($string)/5), $string);
print "@fivers";
print "\n";

@chars = unpack("A1" x (length($string)),$string);
print "@chars";
print "\n";

#result:
good+start+, day day up!
good good start , day day
g o o d g o o d s t a r t , d a y d a y u p !