Check if a user is in a group

Question

I have a server running where I use php to run a bash script to verify certain information of a user. For example, I have a webhosting server set up, and in order to be able to

Answer 1

username='myuser'
if groups "$username" | grep -q -E ' customers(\s|$)'; then
    echo 'yes'
else
    echo 'no'
fi

I have to clear one thing: groups will probably return something like this:

myuser : cdrom floppy sudo audio dip video plugdev fuse

But there is one cornercase when your user is named customers:

customers : cdrom floppy sudo audio dip video plugdev fuse

For example, \bcustomers\b pattern is going to find the username, not the group. So you have to make sure that it is not the first word in the output.

Also, another good regexp is:

grep -q ' customers\b'