Comments on: Bash User Input Validation

By: wayne

wayne — Wed, 28 Sep 2011 00:13:09 +0000

looks like my regular expression was annihilated by your comment form. email me if you want it.

By: wayne

wayne — Wed, 28 Sep 2011 00:09:55 +0000

if this is input validation, shouldn’t it actually check for an appropriate input and inform the user if it is not correct? that is my understanding of what “input validation” means. here is something i wrote up to check to see if a mac address is valid for a given company whose allocation starts with “00:01:32″:

tmp=$(echo $REPLY | grep -E “\” \
| tr -d :)
if [ "x$tmp" == "x" ] ;then
echo “Please enter a valid Brawndo MAC Address.”
exit 1
fi

the very best thing about this is the smiley face at the end of the third line. just sayin…

By: Angie

Angie — Thu, 28 Apr 2011 01:58:11 +0000

@buddyh

For Y/N use ‘case’. Check out scripts under /etc/init.d/ for proper use of ‘case’

By: gmendoza

gmendoza — Wed, 30 Dec 2009 09:48:20 +0000

@Pawan Jaitly: Thanks for your input. I’ll add the Bash method as it certainly is the simplest method!

By: Pawan Jaitly

Pawan Jaitly — Tue, 03 Nov 2009 16:04:59 +0000

A bash way of doing this:

DIRTY=”a dirty string”
CLEAN=${DIRTY//[^a-zA-Z0-9]/}

In this example the dirty characters are spaces. Modify to taste.

By: gmendoza

gmendoza — Thu, 25 Jun 2009 15:33:16 +0000

Apparently tr does not support multibyte characters (yet). Found this post with comments that suggest support for UTF-8 and UTF-16 is coming. See http://tinyurl.com/mqsb69 for more details.

By: Avery

Avery — Wed, 24 Jun 2009 06:43:01 +0000

any clues for using tr to also allow utf-8 characters – the alnum doesn’t seem to okay things like… ñáéíóúçäüö etc…

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.