regex - Combining Regexes -

how can combine regexes?

edit: if exam preparation. question write regex find strings have odd number of a's , number of b's?

i.e. instead of | or, need mechanism emulate and

i have 2 regexes:

1) find odd number of a's:  ^[^a]*a([^a]*a[^a]*a)*[^a]*$  2) find number of b's:  ^([^b]*b[^b]*b)*[^b]*$ 

you can using lookahead expressions (here shown verbose regex since hard read, more on single line):

^                                   # start of string (?=(?:(?:[^a]*a){2})*[^a]*$)        # assert number of (?=[^b]*b(?:(?:[^b]*b){2})*[^b]*$)  # assert odd number of bs .*                                  # match $                                   # end of string 

the last 2 lines can dropped if you're validating - match entire string.