I'll be your huckleberry.
Line by line (well, statement by statement), shall we?

use 5.10.0;
Enables the 'say', 'state', 'switch', and 'indirect' features, but only the 'say' for the Perl 6-style 'say' function is used in this code.

$p=japh;
Stores the string "japh" in $p.

push@a,w();
Pushes the value returned by the sub w() into $a[0]. This is the string 'aeafa7cfdbd58c'.

# @a = ('aeafa7cfdbd58c');

[download]

$s=j4;
Stores the string "j4" in $s.

sub n{"8fbac6c6e252"};
Defines the sub n(), which will return the string '8fbac6c6e252'.

unshift@a,"b4d6c7ea52a7";
The value of index 1 in @a is now "b4d6c7ea52a7". 

# @a = ('bcb3d8dec8dd', 'b4d6c7ea52a7',);

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$k=crypt($s,$p);
Calling the crypt() function on the string "j4" with the salt "japh" returns the value "jaTv2fNDdvcko", which is stored in $k.

$o="aeafa7cfdbd58c";
Store the string "aeafa7cfdbd58c" in $o.

@h=map{sprintf"%x",ord$_}split//, $k;
Split the string in $k into individual characters, and store the ordinal value of each in @h. 

# @h = ('6a', 61, 54, 76, 32, 66, '4e', 44, 64, 76, 63, '6b', '6f',);

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push@a, $o;
Push the value in $o ("aeafa7cfdbd58c") into @a. 

# @a = ('bcb3d8dec8dd', 'b4d6c7ea52a7', 'aeafa7cfdbd58c',);

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$a[3]=pop@a;
This command pops the last value from @a, then pushes it into the array at index 3, resulting in an undefined value at array index 2 (the previous location of that value). 

# @a = ('bcb3d8dec8dd', 'b4d6c7ea52a7', undef, 'aeafa7cfdbd58c',);

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$a[2]=n();
This code pushes the value returned by n(), '8fbac5c5e252', into @a at index 2. 

# @a = ('bcb3d8dec8dd', 'b4d6c7ea52a7', '8fbac5c5e252', 'aeafa7cfdbd58
+c',);

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sub w{"bcb3d7dec8dd"}
Defines the sub w(), which will return the string 'bcb3d7dec8dd'.

$x.=$_ for@a;
Concatenate the values in @a and store in $x. 

# $x = 'b4d6c7ea52a7bcb3d8dec8dd8fbac6c6e252aeafa7cfdbd58c';

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@b=($x=~m/..?/g);
Split $x into 2-character groups, pushing each into @b. 

# @b = ('b4', 'd6', 'c7', 'ea', 52, 'a7', 'bc', 'b3', 'd8', 'de', 'c8'
+, 'dd', '8f', 'ba', 'c6', 'c5', 'e2', 52, 'ae', 'af', 'a7', 'cf', 'db
+', 'd5', '8c',);

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push@z,@h until @z>@b;
Loop through the values of @h, pushing them into @z until @z has more items that @b. 

# @z = ('6a', 61, 54, 76, 32, 66, '4e', 44, 64, 76, 63, '6b', '6f', '6
+a', 61, 54, 76, 32, 66, '4e', 44, 64, 76, 63, '6b', '6f',);

[download]

for(@b){push@japh,hex($_)-hex($z[$n]);$n++;}
This is where the work is done (so to speak). The values in @z are subtracted from the values with corresponding indexes in @b, and the value is pushed into @japh. 

# For each iteration of the loop, here are the values of $n, $_, hex($
+_), $z[$n], hex($z[$n]), and hex($_)-hex($z[$n]):
# undef 'b4'    180     '6a'    106     $japh[ 0] = 74
#  1    'd6'    214     '61'    97      $japh[ 1] = 117
#  2    'c7'    199     54      84      $japh[ 2] = 115
#  3    'ea'    234     76      118     $japh[ 3] = 116
#  4    52      82      32      50      $japh[ 4] = 32
#  5    'a7'    167     66      102     $japh[ 5] = 65
#  6    'bc'    188     '4e'    78      $japh[ 6] = 110
#  7    'b3'    179     44      68      $japh[ 7] = 111
#  8    'd8'    216     64      100     $japh[ 8] = 116
#  9    'de'    222     76      118     $japh[ 9] = 104
# 10    'c8'    200     63      99      $japh[10] = 101
# 11    'dd'    221     '6b'    107     $japh[11] = 114
# 12    '8f'    143     '6f'    111     $japh[12] = 32
# 13    'ba'    186     '6a'    106     $japh[13] = 80
# 14    'c6'    198     61      97      $japh[14] = 101
# 15    'c5'    197     54      84      $japh[15] = 114
# 16    'e2'    226     76      118     $japh[16] = 108
# 17    52      82      32      50      $japh[17] = 32
# 18    'ae'    174     66      102     $japh[18] = 72
# 19    'af'    175     '4e'    78      $japh[19] = 97
# 20    'a7'    167     44      68      $japh[20] = 99
# 21    'cf'    207     64      100     $japh[21] = 107
# 22    'db'    219     76      118     $japh[22] = 101
# 23    'd5'    213     63      99      $japh[23] = 114
# 24    '8c'    140     '6b'    107     $japh[24] = 33

# And the resulting values in @japh:
@japh = ( 74, 117, 115, 116, 32, 65, 110, 111, 116, 104, 101, 114, 32,
+ 
80, 101, 114, 108, 32, 72, 97, 99, 107, 101, 114, 33, );

# For those of you who may have forgotten your handy-dandy ASCII 
# decoder ring, here you go:
# 
# ord   char    ord     char    ord     char
# 32    {space} 33      !       65      A    
# 72    H       74      J       80      P    
# 97    a       99      c       101     e
# 104   h       107     k       108     l
# 110   n       111     o       114     r
# 115   s       116     t       117     u

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say map{chr$_}@japh;
Convert the ordinal values back to ASCII characters and display. 

# Just Another Perl Hacker!

[download]

Nice code, and a fun exercise tracing through to see how it worked. Well done.

In reply to Re: Let's play JAPH by atcroft
in thread Let's play JAPH by stevieb

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