Bash: How do I format these conditions in a while loop?

Question

How do I format the 2 conditions below into one while loop which should ensure that data enter contains at least one alphabetical character and doesn't already exist in the directory /dev/null.

1

#name = "test123"
read -p "Enter you name: " name
until [[ "$name" =~ [A-Za-z] ]]; do
    read -p "Please enter a valid name: " name
done

2

while id -u $name 2>/dev/null>1 ; do # Checks if username already exists
read -p "Please enter valid input: "

I know there are different ways toformat the 2 arguments in the while loop as it depends on the 2 arguments however i am not sure.

I've found this source below which i could proceed to trial an error however I want to know why I choosing to format the condition in such a way.

Bash scripting, multiple conditions in while loop

anubhava · Answer 1 · 2016-03-30T17:06:01.500

2

You can use your loop like this:

while read -r -p "Please enter valid input: " name; do
   [[ $name == *[a-zA-Z]* ]] && { id -u "$name" >/dev/null 2>&1 || break; }
done

echo "Got a good name: $name"

read is used in a while loop which will keel looping until a break is executed inside the loop.
$name == *[a-zA-Z]* will check for presence of an alphabet in input name. * is used for globbing on either side.
id -u command will return 0 if entered name is found in user database and break gets executed when id command fails (username is unique).
>/dev/null 2>&1 is used to suppress stdout/stderr from id command since we only care about return status of id.

edited Mar 30 '16 at 17:06

answered Mar 30 '16 at 16:51

anubhava

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Could you please explain the chosen options for read and why you formatted it this way? – pythontamer Mar 30 '16 at 16:52
What do the asterisks do around the parentheses, why are you using double square brackets for one condition and curly ones for the next. Why have you included 'break'? (I know break ends the loop) – pythontamer Mar 30 '16 at 16:54
Why have you used this way: >/dev/null 2>&1 – pythontamer Mar 30 '16 at 16:55
You've made reference to 'id -i' however in your example you've used 'id -u', furthermore doesn't the double pipe mean 'or'? What does the double pipe mean in this instance. – pythontamer Mar 30 '16 at 17:03
No problem :), what does the double pipe you've used do in this instance? – pythontamer Mar 30 '16 at 17:08
`||` is used for `OR` clause. So `break` executes when `id -u` returns non-zero status – anubhava Mar 30 '16 at 17:11
Why is the while statement referenced after do? – pythontamer Mar 30 '16 at 17:11
`while [[ $name == *[a-zA-Z]* ]] && { id -u "$name" >/dev/null 2>&1 || break; }`; do <--- Something like this – pythontamer Mar 30 '16 at 17:13
You must have done some copy/paste error. Same code works fine on my bash shell. Make sure you're executing it using `bash` – anubhava Mar 30 '16 at 18:02
I am executing in http://www.tutorialspoint.com/execute_bash_online.php and it's not working. – pythontamer Mar 30 '16 at 18:09
What version of bash do you have? I got Bash 4+ – pythontamer Mar 30 '16 at 18:14
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/107771/discussion-between-pythontamer-and-anubhava). – pythontamer Mar 30 '16 at 18:14
This script also worked great on http://www.tutorialspoint.com/execute_bash_online.php – anubhava Mar 30 '16 at 19:46

Bash: How do I format these conditions in a while loop?

1 Answers1