List logged users and how many sessions they have opened.

who_is_logged_in.sh

#!/bin/bash

if [[ $# > 1 ]]; then
    echo "Error: wrong number of arguments"
    exit -1
else
    if [[ $1 == "" ]]; then      
        while read -r line
        do
            USER=$(echo $line | awk '{print $2}')
            TIMES=$(echo $line | awk '{print $1}')
            echo "$USER is logged $TIMES times."
        done < <(w | sed '1,2d' | cut -f1 -d' ' | sort | uniq -c)
    else
        FIRST_LETTER=$1
        while read -r line
        do
            USER=$(echo $line | awk '{print $2}')
            TIMES=$(echo $line | awk '{print $1}')
            echo "$USER is logged $TIMES times."
        done < <(w | grep "^$FIRST_LETTER" | cut -f1 -d' ' | sort | uniq -c)
    fi
fi

HOW TO

Download and make it ready for execution

$ cd $HOME && wget http://bit.ly/1Ui4pbP -O sc1.sh && chmod +x sc1.sh

Run it

$ ./sc1.sh

or just print sessions for users starting with a particular letter, e.g. 'f'

$ ./sc1.sh f