Learn Regex in 4 tweets :)
cat matches cat
ca+t matches caaaaaaaaaaaat but not ct
ca*t matches caaaaaaaaaaaat and also ct
ca{2,4} matches caat, caaat and caaaat
c(at)+ matches catatatatatat
c(at|orn) matches cat and corn
c[ea] matches cat and cet
c[ea]+ matches caaaat and ceeet