CODEWITHSUNDEEP
perl
mkHun
mkHun

Reputation: 5927

What does ~ mean in perl?

Array

my @ar = qw(one two);
print ~@ar,"\n";
#output 18446744073709551613

Scalar (Result is very interesting )

my $ar = "qw(onetwo)"; 
print ~$ar
#Output Please refer the screen shot.

My question is what ~ does?

For array it is giving the some numbers.

For scalar it is giving the some other characters, we I copied the character from terminal and pasted in gedit, the result is after the long spaces characters printed with revers order. I can't delete the characters from last. If I'm trying to delete the spaces,characters are delete one by one(left to right). I can't understand what is going here.?

Upvotes: 1

Views: 143

Answers (3)

nwellnhof
nwellnhof

Reputation: 33618

Unary ~ performs bitwise negation. Numbers are first converted to integers by discarding the fractional part, then each bit in the binary representation is flipped. So on a 64-bit system, you'll get:

$ perl -e 'printf "%x\n", ~0'
ffffffffffffffff

Double negation can be used to convert non-negative numbers to integers in a terse but unreadable way:

$ perl -le 'print ~~1.8'
1

Evaluated in scalar context, an array yields the number of elements, so for a two-element array, ~@a is equivalent to ~2.

When operating on strings, each bit in the binary representation of the string is flipped:

$ perl -le 'print unpack("B*", "A"), "\n", unpack("B*", ~"A")'
01000001
10111110

$ perl -le 'print unpack("H*", "onetwo"), "\n", unpack("H*", ~"onetwo")'
6f6e6574776f
90919a8b8890

6f is the hex ASCII code for o and 90 is the negated hex value. Since the MSB of each byte is flipped, you typically get garbage when printing the bitwise negation of a string.

Upvotes: 6

PerlDuck
PerlDuck

Reputation: 5720

From the docs:

Symbolic Unary Operators

[...]
Unary "~" performs bitwise negation, that is, 1's complement. For example, 0666 & ~027 is 0640.
[...]

Albeit it looks different, I assume ~@ar does a bitwise negation of the number of elements in @ar:

print ~2, "\n";
18446744073709551613

Upvotes: 4

Wep0n
Wep0n

Reputation: 402

Taken from perldoc manpage

Unary "~" performs bitwise negation, that is, 1's complement. For example, 0666 & ~027 is 0640.

However, the ~ operator has a bunch of other functions as well, for example the =~ operator is for applying a regular expression to a scalar.

In general, working with operators is a pretty messy ordeal, I suggest you consult the linked manpage if you have a question about them.

Upvotes: 1

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