Comments on: Bash User Input Validation

By: buddyh

buddyh — Tue, 21 Oct 2008 11:27:33 +0000

As a learning admin this is great info. I thought there was a way to limit the input to a specific set of characters. I just need to have the user input a Y or N in either upper or lower case and reject any other entry. Thinking of using a while loop till a correct char is entered as an alternative.
Tx in advance

By: al

al — Thu, 16 Oct 2008 22:08:27 +0000

Thanks a bunch - I’ll remember this one.

By: gmendoza

gmendoza — Thu, 16 Oct 2008 18:17:41 +0000

Easy… use sed to strip beginning and trailing spaces:

tr -cd ‘[:alnum:] [:space:]‘ | sed -e ’s/^[ ]*//’ -e ’s/[ ]*$//’

By: al

al — Thu, 16 Oct 2008 14:18:49 +0000

I actually did that. But please consider following - someone puts in the username “al_the_on___the_sea”. I wouldn’t want to shrink it to “altheon” after cutting 10 spaces, but would rather have “al_the_on” . This would make it 9 char, but if the last space was left “al_the_on_” it would be user difficult to use such a name. I tried different ways, but nothing easy came about. If you have some sort of solution, I would be all ears. Also from programming perspective, one would have to check from the back of the string moving forward until first alphanumeric character was found.

By: gmendoza

gmendoza — Wed, 15 Oct 2008 19:55:36 +0000

Hi there. The example in the post explains that alphanumeric and spaces are allowed. Simply omit the [space] value, and you’ll be left strictly with alphanumeric. For example:

tr -cd ‘[:alnum:]‘

By: al

al — Wed, 15 Oct 2008 19:49:38 +0000

I had something similar to complete not too long ago. I found it very hard to manipulate last characters going backwards in order to edit spaces. Example 10 character password al——–, where “-” is equal to space. In order to check for that and concatenate to just “al” instead of “al ” - what approach would you use?

By: Amarendra

Amarendra — Fri, 05 Sep 2008 10:53:54 +0000

Interesting, and neat, especially the white-listing part.