Ask HN: Any ideas what code this is? |
Ask HN: Any ideas what code this is? |
$_='^#(/||/@!@[{@:^[-['^";@@@\\>])@.".
"{)/];)^{";$,+=(++$,);$_.=">&$,";`$_`;
= Assignment Operator.
. Concatenation Operator.
.= Concatenate and Assign.
^ Binary XOR. The binary "^" and "|" operators have lower precedence than relational operators like concatenate.
' Text between single quotes is an uninterpreted string.
" Text between double quotes is an interpreted string.
; Statement terminator, just like C, java, javascript, ...
$ man perlvar
$_ The default input and pattern-searching space. A lot of perl code operates on this variable by default.
$, The output field separator for the print operator. If defined, this value is printed between each of print's arguments. The default is "undef".
The first statement is:
$_='^#(/||/@!@[{@:^[-['^";@@@\\>])@."."{)/];)^{";
String1: '^#(/||/@!@[{@:^[-['
String2: ";@@@\\>])@."
String3: "{)/];)^{"
So we get:
Result = String1 XOR String2 CONCAT String3
Since XOR has a lower precedence than Concatenate, we Concatenate first and then do the XOR.
# First String:
$_='^#(/||/@!@[{@:^[-[';
printf "HEX1: %*v2.2X\n", ' ', $_;
print "STR1: " . $_ . "\n";
$str1 = $_;
# OUTPUT:
# HEX1: 5E 23 28 2F 7C 7C 2F 40 21 40 5B 7B 40 3A 5E 5B 2D 5B
# STR1: ^#(/||/@!@[{@:^[-[
# Second String:
$_=";@@@\\>])@.";
printf "HEX2: %*v2.2X\n", ' ', $_;
print "STR2: " . $_ . "\n";
$str2 = $_;
# OUTPUT:
# HEX2: 3B 40 40 40 5C 3E 5D 29 40 2E
# STR2: ;@@@\>])@.
# Third String:
$_="{)/];)^{";
printf "HEX3: %*v2.2X\n", ' ', $_;
print "STR3: " . $_ . "\n";
$str3 = $_;
# OUTPUT:
# HEX3: 7B 29 2F 5D 3B 29 5E 7B
# STR3: {)/];)^{
# Since the "^" binary XOR operator has lower precedence
# than the "." concatenation operator, XOR str2 and str3 to
# get the Fourth String:
$_ = $str2 . $str3;
printf "HEX4: %*v2.2X\n", ' ', $_;
print "STR4: " . $_ . "\n";
$str4 = $_;
# OUTPUT:
# HEX4: 3B 40 40 40 5C 3E 5D 29 40 2E 7B 29 2F 5D 3B 29 5E 7B
# STR4: ;@@@\>])@.{)/];)^{
# Now we can do a binary XOR on Sring #1 and String #4 to
# get Fifth String:
$_ = $str1 ^ $str4;
printf "HEX5: %*v2.2X\n", ' ', $_;
print "STR5: " . $_ . "\n";
$str5 = $_;
# OUTPUT:
# HEX5: 65 63 68 6F 20 42 72 69 61 6E 20 52 6F 67 65 72 73 20
# STR5: echo Brian Rogers
# This is wickedly bad juju. The "(++$,)" portion increments an
# undefined variable and would normally be an error, but with errors and
# warnings shut off, it increments an undefined variable to 1, then adds
# it to itself with "+=" to get 2.
$,+=(++$,);
# Here we concatenate shell redirection to stderr, which is file
# descriptor 2, with the usual ">&2" since "$," now equals 2.
$_.=">&$,";
print "\n";
printf "HEX-: %*v2.2X\n", ' ', $_;
print "STR-: " . $_ . "\n";
# OUTPUT:
# HEX-: 65 63 68 6F 20 42 72 69 61 6E 20 52 6F 67 65 72 73 20 3E 26 32
# STR-: echo Brian Rogers >&2
# Finally, the statement is evaluated in the shell:
`$_`;
$_ = 'somestring';
`$_`; // backticks are shell or exec(), $_ is the previous string.
;$,+=(++$,); looks like a for loop
looks like php to me - backticks work in perl, bash and php
$_ is a special var in Bash and Perl.
The '.' char is for string concat in Perl and PHP
So, I think this is perl.
The first statement evaluates to: "echo Brian Rogers >&2" The second statement `$_` runs that command.
The end result is that this line of code prints:
Brian Rogers
$_='^#(/||/@!@[{@:^[-['^";@@@\\>])@.".
"{)/];)^{";$,+=(++$,);$_.=">&$,";
print "$_";
echo Brian Rogers >&2