Con de MIME
This is a french joke 😃
This Japh is from Reynold Scem
use MIME::Base64;(eval decode_base64('am9pbignJywobWFwe2NocigpfShncmVwL1xTLyxzcGxpdCgvKC4uLikvLCcwNzQxMTcxMTUxMTYwMzIwOTcxMTAxMTExMTYxMDQxMDExMTQwMzIwODAxMDExMTQxMDgwMzIxMDQwOTcwOTkxMDcxMDExMTQwNDQnKSkpKQ=='))=~/.*/;print$&
This one... We can't guess what will happen when we eval this encoded string...
It uses actually 2 steps to produce the Japh, first base64 encoding, that we can check with base64 -d
:
echo "am9pbignJywobWFwe2NocigpfShncmVwL1xTLyxzcGxpdCgvKC4uLikvLCcwNzQxMTcxMTUxMTYwMzIwOTcxMTAxMTExMTYxMDQxMDExMTQwMzIwODAxMDExMTQxMDgwMzIxMDQwOTcwOTkxMDcxMDExMTQwNDQnKSkpKQ==" | base64 -d
join('',(map{chr()}(grep/\S/,split(/(...)/,'074117115116032097110111116104101114032080101114108032104097099107101114044'))))
From decoding I got the actual Perl code to evaluate and I feel a bit better now 😁
The code Japh string creation code looks like this :
my $str = eval { join('', ( map {chr()} ( grep/\S/, split(/(...)/, '074117115116032097110111116104101114032080101114108032104097099107101114044')))) };
Then in the perl code there is map
, chr
(convert value to char), grep \S
(match all non whitespace), split(/(...)/,
(split per 3 chars).
It's a nice showcase 😃 even if a lot of things are actually useless and only there to obfuscate the Perl code.
The Japh creation could be simply reduced to :
my $str = join('', map {chr()} ( split(/(...)/, '074117115116032097110111116104101114032080101114108032104097099107101114044')));
The join
seems useless but forces the string context.
So here is the complete Japh unfolded :
use MIME::Base64;
# Base 64 encoding
# am9pbignJywobWFwe2NocigpfShncmVwL1xTLyxzcGxpdCgvKC4uLikvLCcwNzQxMTcxMTUxMTYwMzIwOTcxMTAxMTExMTYxMDQxMDExMTQwMzIwODAxMDExMTQxMDgwMzIxMDQwOTcwOTkxMDcxMDExMTQwNDQnKSkpKQ==
# join('',(map{chr()}(grep/\S/,split(/(...)/,'074117115116032097110111116104101114032080101114108032104097099107101114044'))))
my $str = eval { join('', ( map {chr()} ( grep/\S/, split(/(...)/, '074117115116032097110111116104101114032080101114108032104097099107101114044')))) };
# Take 3 chars (...), do not keep space (\S), tranform to corresponding string representation, concat without space, eval (useless)
$str =~ /.*/; # Match everything
print $&; # The string matched by the last successful pattern match
Maybe you noticed that there is also some fun with regex match and captured match print. It is just for fun ! 😃
Open Format Write
open(P,"|perl");print P"format=\nJust another Perl hacker,\n.\nwrite"
After some ordering, it looks like this :
open(P,"|perl");
print P "
format=
Just another Perl hacker,
.
write"
There are 2 tricks here :
- The open filehandle to another perl process
- The "format", an old Perl function that is less and less used nowadays
It is actually the same than :
format=
Just another Perl hacker,
.
write
Kisses
Here is a simple but interesting japh with some kisses inside ! 😘 😘 😘 😘
@_=("Just another Perl hacker," =~ /(.*) (.*) (.*) (.*)/);print"@_";
This japh demonstrates default variable @_
and matching.
I think it can be rewritten like this :
my $str = "Just another Perl hacker,";
my @a = $str =~ /(.*) (.*) (.*) (.*)/;
print join(" ", @a) . "\n";
Perl developers should be comfortable with this form 😄
It's probably time to address regex greediness.
This kind of greedy .*
matches is "dangerous" (depends what you want), because it will try to match as much as possible.
For instance "Just another Perl 7 hacker,"
with the greedy version will produce a string split like the following :
Just another
Perl
7
hacker,
(because the .*
happily eats also the space)
x25
Let's have a look at a simple japh using printf
, x
and ASCII conversion.
printf "%c"x 25,74,117,115,116,32,97,110,111,116,104,101,114,32,80,101,114,108,32,104,97,99,107,101,114,44;
The operator x
is magic :
printf "perl " x 10
Will produce :
perl perl perl perl perl perl perl perl perl perl
In the japh, the x 25
is applied to "%c"
, therefore it can be translated like this :
printf("%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c%c",74,117,115,116,32,97,110,111,116,104,101,114,32,80,101,114,108,32,104,97,99,107,101,114,44);
Arrow here
Again a printf "%c"
but this time the input being in hexadecimal and the whole thing being stored in a string assignment :
$_ = <<'-- '; s/../printf "%c",hex($&)/ge;
4a75737420616e6f74686572205065726c206861636b65722c
--
It starts with a "here-doc" delimited by --
(dash + dash + space not represented by DevTo).
What is weird, is that the whole thing looks only like a string assignation...
Actually, the printf
inside the regex will print to stdout. At the end $_
does not even contains the string, but sprintf
would have done the job.
And what is exactly s/../printf "%c",hex($&)/ge
?
-
s///
is for substitution. -
$&
is what have been matched. - The
/e
modifier allows the right part of the substitution to be actually executed as normal Perl code. - The
/g
modifier is the "looping modifier" or "global modifier" and just repeats the match along the string !
Finally, I propose this rewrite of the japh :
my $str = "4a75737420616e6f74686572205065726c206861636b65722c";
while($str =~ /../g) { # Or $str =~ s/..//
printf("%c", hex($&));
}
Cristal clear like this isn't it ?
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