syntax question in bash

Aim is that script should exclude user1-3 from executing...

if [ $currentuser != 'user1' -a $currentuser != 'user2'  -a $currentuser != 'user3'  ]; then echo Fine; fi

or

if [ $currentuser == 'user1' -o $currentuser == 'user2'  -a $currentuser == 'user3'  ]; then echo Sorry; fi

Not 100% sure what the intent is on this. If I understood correctly, and you have something that you want to run for the currently logged in user unless it is one of a few users, this ought to work pretty well. You can use a pre-defined array of skippable users and a for loop to compare each to the current user. This scales well since you can just continually add or remove users to the array if/whenever needed. Also, you can wrap it in a function for easy portability across multiple scripts.

#!/bin/bash

#---FUNCTIONS---------------------------------------------------------------------------

# Gets the current console user
getConsoleUsername()
{
/usr/bin/python -c 'from SystemConfiguration import SCDynamicStoreCopyConsoleUser
user = (SCDynamicStoreCopyConsoleUser(None, None, None) or [None])[0]
user = [user,""][user in [u"loginwindow", None, u""]]
print(user)'
}

# Skips users in a predefined array of skippable users
isSkippable()
{
    local _skip_users _console_user _skip

    # Define an array of all users that should be skipped
    _skip_users=("user1" "user2" "user3")

    # Get the current console user
    _console_user="$(getConsoleUsername)"

    # Loop through the array of skippable users
    for _skip in "${_skip_users[@]}"; do

        # Return success (0) (i.e. the user is skippable) if the console
        # user matches any user in the array of skippable users
        [ "$_console_user" = "$_skip" ] && return 0
    done

    # Return failure (1) (i.e. user is not skippable) if
    # the user is not in the array of skippable users
    return 1
}

#---START SCRIPT------------------------------------------------------------------------

# Check if user shold be skipped
if isSkippable; then

    # If the user is skippable, report and exit
    echo "User is being skipped"

else
    ######################################################
    # If the user is not skippable, do the main thing here
    ######################################################
fi

exit 0