mjhjmtu

I am creating a script for automated tasks regarding LVM. In the script, I want user to input the VG name and it has to be unique. How to create a loop so that if user enters a VG name that already exists in the system it doesn't move ahead and keeps asking for the VGname until its unique.

The function I am using for VG creation is mentioned below:

vg_create() grep -cw $vgname`

 if [ $vg_match -eq 1 ]; then
 echo -e "$vgname already exists. Kindly enter new name.n"
 else
 echo -e "$vgname doesn't exist in system and will be created.n"
 fi
 read -p "Enter the name of the physical volume on which volume group to be created: " pv2_name
 printf "n"
 vgcreate $vgname $pv2_name

 printf "n"
 printf "The new list of volume groups in the system are: n"
 vgs 

In general:

# loop until we get correct input from user
while true; do
 # get input from user

 # check input

 # break if ok
done

Or, a bit more fleshed out:

# loop until we get correct input from user
while true; do
 read -r -p "Give your input: " answer

 # check $answer, break out of loop if ok, otherwise try again

 if pvs | awk 'NR > 2 print $2' | grep -qw -e "$answer"; then
 printf '%s already existsn' "$answer" >&2
 else
 break
 fi
done

Note: I have no idea what pvs does.

Here's two different ways to check for the existence of a VG:

1. attempt to read the VG directly vgs --readonly "$vgname"; if that command succeeds, the VG already exists.


2. If the vgname is listed in the output from vgs, the VG already exists.

Note that the second method specifically asks vgs to not print the heading and to only print the VG name field. The name is (on my system) often printed with leading and trailing spaces, which is why the grep expression looks the way it does.

read -p "Enter the name of the volume group to be created: " vgname
while vgs --readonly "$vgname" > /dev/null 2>&1
do
 read -p "Enter the name of the volume group to be created: " vgname
 if vgs --noheadings -o vg_name | grep -q "^ *$vgname *$"
 then
 printf "That VG name is already taken; try something elsen" >&2
 fi
done