How this regex work?

Question

can you explain this regular expression.

$price = "...555.55";
$price  = preg_replace('/^./', '', $price);

output:

 $price = ..555.55;

Answer 1

The regex '/^./' matches any character at the beginning of the string.

• dot(.) matches any character except the newline character, and
• caret(^) is used to match at the beginning.

So, your preg_replace is replacing any character at the beginning with an empty string. So, ...555.55 becomes ..555.55 after replacing the first ..

If you just want to replace all the dots(.) from the beginning, then you have to escape the . in your regex. Since simply using . will match any character. Also, you need to use some quantifier - * or + to replace more dots(.).

So, your regex would be:

preg_replace('/^[.]+/', '', $price);

or:

preg_replace('/^\.+/', '', $price);

Answer 2

/^./ matches the first character after the start of the string.

• / and / delimit the regex.
• ^ matches the position at the start of the string,
• . matches any character unless it's a linebreak).

That match will be replaced by the empty string ('').

If you want to replace the first three characters:

$price = preg_replace('/^.{3}/', '', $price);

If you want to replace all dots at the start of the string, you need to escape them and apply a quantifier (+ meaning "one or more"):

$price = preg_replace('/^\.+/', '', $price);

If you want to replace all non-digits at the start of the string (which might make more sense):

$price = preg_replace('/^\D+/', '', $price);