a=(`fold -1`)
op=('+' '-')
for o1 in ${op[@]}
do
    for o2 in ${op[@]}
    do
        for o3 in ${op[@]}
        do
            if((a[0]${o1}a[1]${o2}a[2]${o3}a[3]==7))
            then
                echo ${a[0]}$o1${a[1]}$o2${a[2]}$o3${a[3]}'=7'
                exit
            fi
        done
    done
done