Find out if a Regex could match - regex

Question

Lets say P is a regex pattern defined as "AB" where A,B are subpatterns. There is a string T which is tested against pattern P. I want to find out if T is a partial match of P, this means T machtes against A but not B since it is not long enough to match B. T could be a match if it was combined with a string U which is matched by B.
var A = "[a-z]{3}";
var B = "[0-9]{2}"
var P = A + B;
var T = "abc";
var U = "20";
var macthes_T = regex(P, T); // false
var matches_U = regex(P, U); // false
var matches_TU = regex(P, T + U); // true
var couldMatch_T = magic(P, T); // true
var couldMatch_U = magic(P, U); // false
var couldMatch_TU = magic(P, T + U); // true
Now I want to doe this recursive on A since its the "start" of P and "implement" the magic function for input T, which would look like this:
var A_1 = "[a-z]";
var A_2 = "[a-z]";
var A_3 = "[a-z]";
var A = A_1 + A_2 + A_3;
// T="" would return false
// T="a" would return true
var hasChar(T) {
return length(T) > 0;
}
// T="ab" would return a and T is "b"
var getChar(T) {
var c = T[0];
T = substring(T, 1);
return c;
}
// Let x element of [a-z]
// would return true for "", "x", "xx", "xxx"
// would return false for any other input T
var magic_A(T) {
if(!hasChar(T)) {
return true;
}
if(!regex(A_1, getChar(T))) {
return false;
}
if(!hasChar(T)) {
return true;
}
if(!regex(A_2, getChar(T))) {
return false;
}
if(!hasChar(T)) {
return true;
}
if(!regex(A_3, getChar(T))) {
return false;
}
return true;
}

Answer 1

umm something like this?
\b(a|ab)[a-z]*
this one check if there's a or ab, then any char between a-z following behind and wrap the whole word as matching
http://regexr.com/3aa5n
just noticed that your code won't work with regex
here's some reference http://www.dotnetperls.com/regex-match