Is there anything the shell can't do?

 
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Operating Systems OS X (Apple) Is there anything the shell can't do?
# 1  
Old 05-01-2014
Is there anything the shell can't do?

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...
Code:
#/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:-
Code:
Enter your full name:-
Barry Walker
Enter your age:-
63
Hi Barry Walker, you are 63 years old.
AMIGA:barrywalker~> _

This User Gave Thanks to wisecracker For This Post:
# 2  
Old 05-01-2014
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  
Old 05-01-2014
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  
Old 05-01-2014
Both of them have eval() functions which probably can but really shouldn't do everything, yes.
# 5  
Old 05-01-2014
Shell expansion is quite capable Smilie
Code:
./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 Smilie Smilie

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

Last edited by sea; 05-01-2014 at 09:55 PM..
# 6  
Old 05-02-2014
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...
Code:
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...
This User Gave Thanks to wisecracker For This Post:
# 7  
Old 05-03-2014
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
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