Why does ltrim remove one character when the second argument contains an operator sign? [duplicate]

Question

If I do:

ltrim('53-34567', '53-');
ltrim('53+34567', '53+');
ltrim('53*34567', '53*');

I get 4567 as the result and not 34567. What's the explanation for this behavior?

Answer 1

ltrim('53-34567', '53-');

There is a 5 at the begining of '53-34567' so it is removed.

There is a 3 at the begining of '3-34567' so it is removed.

There is a - at the begining of '-34567' so it is removed.

There is a 3 at the begining of '34567' so it is removed.

There is nothing in '53-' at the begining of '4567' so it stopped.

This is the same behaviour than a trim() by removing unwanted trailing characters. In example, trim(" lots of spaces "); will return "lots of spaces" by removing trailing and leading spaces but will keep the inner ones.

Answer 2

This is because ltrim trims characters from a second param.

How it works:

1. start read a string(first param) from left.
2. check if first-left char is in a list of 'character-to-trim' list.
3. If 2 is YES - trim it and go to step 1.
4. if 2 is NO - exit.