Is there anything the shell can't do?

UNIX macOS
1

The number 2014 thread got me thinking about obfuscation...

This is a DEMO to use variables only to create a working program.

Yes I know there will be raised eyebrows but this I have found highly interesting.

This is not obfuscated per-se as I have given each alpha-numeric character a similar
alpha-numeric variable...

It certainly is easily crackable but makes for a DEMO of the power of the shell...

I feel as though I am no longer an amateur, but semi-pro at shell scripting... ;o)

Enjoy...

#/bin/bash
# strings.sh
# OSX 10.7.5, default bash terminal.
for n in a b c d e f g h i j k l m n o p q r s t u v w x y z
do
	eval A$n="$n"
done
for n in A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
do
	eval A$n="$n"
done
num=0
for n in a b c d e f g h i j
do
	eval B$n="$num"
	num=$((num+1))
done
Bk=' ';Bl='!';Bm='"';Bn='#';Bo='$';Bp='%';Bq='&';Br="'"
Bs='(';Bt=')';Bu='*';Bv='+';Bw=',';Bx='-';By='.';Bz='/'
Ca=':';Cb=';';Cc='<';Cd='=';Ce='>';Cf='?';Cg='@';Ch='['
Ci='\';Cj=']';Ck='^';Cl='_';Cm='`';Cn='{';Co='|';Cp='}'
Cq='~'
# A program using $string format only...
#
# clear
$Ac$Al$Ae$Aa$Ar
# eval name=""
$Ae$Av$Aa$Al$Bk$An$Aa$Am$Ae$Cd$Bm$Bm
# eval age=""
$Ae$Av$Aa$Al$Bk$Aa$Ag$Ae$Cd$Bm$Bm
# eval printf "Enter your full name:-\n"
$Ae$Av$Aa$Al$Bk$Ap$Ar$Ai$An$At$Af$Bk$Bm$AE$An$At$Ae$Ar$Bk$Ay$Ao$Au$Ar$Bk$Af$Au$Al$Al$Bk$An$Aa$Am$Ae$Ca$Bx$Ci$An$Bm
# read name
$Ar$Ae$Aa$Ad$Bk$An$Aa$Am$Ae
# eval printf "Enter your age:-\n"
$Ae$Av$Aa$Al$Bk$Ap$Ar$Ai$An$At$Af$Bk$Bm$AE$An$At$Ae$Ar$Bk$Ay$Ao$Au$Ar$Bk$Aa$Ag$Ae$Ca$Bx$Ci$An$Bm
# read age
$Ar$Ae$Aa$Ad$Bk$Aa$Ag$Ae
# eval printf "Hi Barry Walker, you are 63 years old.\n"
$Ae$Av$Aa$Al$Bk$Ap$Ar$Ai$An$At$Af$Bk$Bm$AH$Ai$Bk$name$Bw$Bk$Ay$Ao$Au$Bk$Aa$Ar$Ae$Bk$age$Bk$Ay$Ae$Aa$Ar$As$Bk$Ao$Al$Ad$By$Ci$An$Bm

Results:-

Enter your full name:-
Barry Walker
Enter your age:-
63
Hi Barry Walker, you are 63 years old.
AMIGA:barrywalker~> _
1 Like
2

Eval's ability to do anything isn't always a good thing. More often than not its a problem -- using it when not necessary means if `rm -Rf ~/` ends up inside your data somehow eval will execute that.

3

Hi Corona688...

True, but I did say it would raise a few eyebrows.

I proper piece of code would intercept the backticks and other shell specific stuff before it sets about decoding/printing it. I didn't put it in but a loop to filter the inputted values to alpha-numeric plus space(s) only would be possible...

I never even expected this to work however, it was an exercise to find the limits of the shell...

Can Python 3.4.x do it?

Perl?

4

Both of them have eval() functions which probably can but really shouldn't do everything, yes.

5

Shell expansion is quite capable :slight_smile:

./Included_Functions/module.dev.prj:				cmd="$(CAPS $typ)_New $lbl"

That is making the select 'ed $typ to capital chars using the function named CAPS , to this the string _New is added and the variable argument $lbl is passed to this expaned new function.
In this example, the typ would be a file that were sourced and contained the function 'TYP_New', which then would be executed upon the call of $cmd

But you guys already done more crazy things :stuck_out_tongue: :b:

EDIT:
At first thought it'd fit, now i cant delete.

6

Hi Corona688...

Although I am using eval in some commands the clear and read do not...
Remember also eval was generated entirely from variables not as a command per-se...

This is an equivalent in python trace...

Last login: Fri May  2 07:26:12 on ttys000
AMIGA:barrywalker~> python3
Python 3.3.2 (v3.3.2:d047928ae3f6, May 13 2013, 13:52:24) 
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> a="t"
>>> b="y"
>>> c="p"
>>> d="e"
>>> e="("
>>> f=")"
>>> type(a)
<class 'str'>
>>> a
't'
>>> b
'y'
>>> c
'p'
>>> d
'e'
>>> e
'('
>>> f
')'
>>> abcdeaf
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'abcdeaf' is not defined
>>> _

You get my point...

OO languages do not seem to lend themselves to the shell's flexibility...

1 Like
7

To answer your question from the thread title: the shell is not good in math. Try to do a FFT or any other type of signal processing algorithm and you get to its limits quite quickly.

That is not to say i don't like shells. Not at all. There are just problems where other languages are better suited. I'd say: put shell, C and Assembler (maybe replacing C with FORTRAN) into your toolbox and there is absolutely no programming task you aren't well equipped for.

bakunin

8

I was expecting that, but one can place __inline_assembly__ or __inline_C__ source code inside a shell script as part of the script, extract and save them, call the command gcc or derivatives thereof, compile them and then run them in the same shell script if required; so IMO the shell is still all powerful... ;o)

It is my language of choice now that I am getting to grips with it... :slight_smile:

1 Like