What would be the regular expression that can search for a Pattern, having 8 characters out of which atleast 1 digit, 1 lower case, 1 upper case letter and 1 special character must be there. But these can occur at any place randomly. Please help me out.
I'm using find $dir -name "*.txt" -exec egrep -ni "[a-z]+[A-Z]+[0-9]+['\~', '\!', '\$', '\%', '\^', '\&', '\-', '\=',' \.', '\:', '\;']" {} \; -print
But this is working only for pattern that begins with lower then upper then digit and then special characters. What if they can happen at any random place... 
Thanks in advance...