How to check the user input to be valid using shell script?

Shell Programming and Scripting
1

How to check the user input to be valid using shell script?

The valid input is in the format like as follows.

  1. It can only have r,w,x or a hyphen and nothing else.
  2. ensure the r, w, x are in the correct order.

for example: rwxr-xr-x is a valid format.

Thanks

2

First, your input (obviously a filemode mask) has more structure: the "r" can only appear in the 1nd, 4th or 7th place, the "w" can only appear in the 2rd, 5th or 8th place, etc.

Construct a regular expression for this and compare the input string against this regexp:

typeset input=""

print - "Enter input string: " ; read input
if print - "$input" | grep -q '^[-r][-w][-x][-r][-w][-x][-r][-w][-x]$' ; then
     print - "input: $input \tstatus: OK"
else
     print - "input: $input \tstatus: Not OK"
fi

I hope this helps.

bakunin

1 Like
3

If we're being picky (and I do love to be picky), you should add the sticky, setuid, and setgid flags too.
Resulting in:
^[-r][-w][-xXs][-r][-w][-xXs][-r][-w][-xXt]$
(The capital letter X is where you've got a forth byte set but no execute).

1 Like
4

Thank you 2.
I got your idea although I can not run your code due to compile error.
Is there any convenient command to convert or substitute "rwxr-xr-x" to be "111101101"?
That means "change "r","w","x" to be "1", "-" to be "0".
After that, I want to change binary to octal format by "bc"? Is it a good method by "bc"?
I am a beginner. thanks for help.

5

What do you mean by "compile error"? What i wrote was Korn-Shell code. Which programming language are you using? (If not a shell, you are probably in the wrong forum. Say so and i transfer the thread to where it belongs.)

I hope this helps.

bakunin

6

Hi bakunin,

I am a beginner and only use bash shell. I got your idea and changed it to bash shell. It works. Thank you very much.