Question

I want to execute a certain bash script when a certain user logs in.
I thought of calling the script in the initialization file of that user e.g. .bashrc, but this is not applicable, as in real life others shouldn’t be allowed to write in users initialization files.
How can I do this?

Answer 1

I could solve it using the comman finger in an infinite loop and when the lines output of the command increase that means that someone logged in and then I can handle that by doing whatever I want with this user, here is the code:

#! /bin/bash
n=0;
while(true)
do
    if [ $n -gt `finger | awk 'END{print NR}'` ]
    then
        mailx -s "hey you" `awk  'END{print $1}'` < mailBody
    fi 
    n=`finger | awk 'END{print NR}'`;   
done

Note: you can initialize n with n=${finger | awk 'END{print NR}'} to avoid considering that someone logged in at the beginning of script execution,or whatever you want.