SH Write a file with contents without any special chars

Question

So, I've got a challenge and it's as follows.

You can access a normal shell(sh) on clean RHEL 6 installation. Write arbitrary content to file.txt, but without the following characters.

# & \ + - % @ = : ; , . ' " ^ ` ~ _ | ! / ? * $ # < > [ ] { } ( )

I can use like touch file or rm file but touch file.txt or echo content > file.txt is not allowed due to . and >.

Is this even possible?

Answer 1

This is quite simple: check for python, perl or any interpreted language availability, then launch the interpreter and just code it !

Answer 2

First having a look on permited chars:

00 E ''         10 E $'\020'    20 E \     46 - F     56 - V     6C - l      
01 E $'\001'    11 E $'\021'    30 - 0     47 - G     57 - W     6D - m      
02 E $'\002'    12 E $'\022'    31 - 1     48 - H     58 - X     6E - n      
03 E $'\003'    13 E $'\023'    32 - 2     49 - I     59 - Y     6F - o      
04 E $'\004'    14 E $'\024'    33 - 3     4A - J     5A - Z     70 - p      
05 E $'\005'    15 E $'\025'    34 - 4     4B - K     61 - a     71 - q      
06 E $'\006'    16 E $'\026'    35 - 5     4C - L     62 - b     72 - r      
07 E $'\a'      17 E $'\027'    36 - 6     4D - M     63 - c     73 - s      
08 E $'\b'      18 E $'\030'    37 - 7     4E - N     64 - d     74 - t      
09 E $'\t'      19 E $'\031'    38 - 8     4F - O     65 - e     75 - u      
0A E $'\n'      1A E $'\032'    39 - 9     50 - P     66 - f     76 - v      
0B E $'\v'      1B E $'\E'      41 - A     51 - Q     67 - g     77 - w      
0C E $'\f'      1C E $'\034'    42 - B     52 - R     68 - h     78 - x      
0D E $'\r'      1D E $'\035'    43 - C     53 - S     69 - i     79 - y      
0E E $'\016'    1E E $'\036'    44 - D     54 - T     6A - j     7A - z      
0F E $'\017'    1F E $'\037'    45 - E     55 - U     6B - k     7F E $'\177'

... Hmmm this is short!

Then

• So using bash variables are not possible, perl do require a lot of signs, even python, without : and =, we're short...
• using tar and cpio will require - on command line,
• using uudecode will require first data line to contain - and .
• same with munpack with a lot of : and some ="--",
• dd, tee and so on will require dot for extension.... ( Maybe this: tee file܂txt (Note the dot ܂ is UTF-8 ܂, not a real dot .), then Hello world and Ctrl+d, but no comment)
• If possible using an editor who will automatically add .txt extension

No.

From there You have to browse all your FS to find some alternative way or language, like apl, brainfuck, perligata...

Answer 3

This may be a moot point if your challenge rules explicitly say you need a .txt in the file name but..

As this is a Linux distro I don't believe the extension should hold so much significance as the file will still be considered an ASCII text file provided that the first two bytes of the file do not combine to create a shebang or are other magic characters that would otherwise alter the interpretation of the file. See this thread for further explanation.

You should be fine to use tee to create file, write all text to it without issue and then check that it is still a text file by running file file.