^[.-a-z0-9A-Z] what is the meaning of the given regular expression.

Answer 1

it's not a valid regular expression...

square braces are use to enclose class character.

inside such classe, the dash (-) has a special meaning until it is placed at very first or last place...

in any other cases, it define a character range ([a-z] match any character in the range of 'a' to 'z' both included)

^ at start of a regex match the string start, while at start inside a character class match any char not in the defined class (negate operator)

Also, some special meaning char such as dot (.) outside a char class (matching any char) loose its special meaning inside a char classe (and match only the dot char itself)

Answer 2

~ swim ~
yes, we could modify it to make it valid (that's why my first post explain how are used char classes and other related things to OP code sample ;)

Without the dot ([-a-z]) is valid and define all chars in a to z range AND the dash (-) wich at first or last place isn't interpreted as an operator defining a range...

But in the case of the unmodified regex provided by OP, that cannot be determinated how to interpret (range between dot char and a plus dash char and z or dot and dash plus range between a and z? many more possibilities with the complete regex, but [.-a-z] seems enough to prove it ^^)

Also negate char class, as I know, could be only done for the whole class (expect by using special char classes inside, such as \W or \S) through the use of the ^ special meaning operator at start of a char class (everywhere else inside a char clasd it would match the ^ char ;))

Answer 3

~ swim ~ :D my bad ^^
I was quickly typing the regex in a js script to confirm my knowledge based theory before my first post, and didn't read the error description given by either js linter and by running the code... but I was forgetting to close my regex literal with an ending slash (/)... so the error was unrelated to the regex itself but to my mistake ;P

You're right, seems to be valid, and to be disambiguated as a char class for (in order) any of dot, dash, a to z, 0 to 9, and A to Z chars :) (probably a not well known and not well documented specification ^^)

Answer 4

Eliya Ben Baruch and Lean Mijares : look carefully... how would you interprete the range [.-a-z] ?
As I said, this regex is invalid ;P

Answer 5

I talk about what I know from Java.
It's like making a list of all the values from a to z (lowercase), 0 to 9, A to Z (uppercase).
And in Java it's being used to replace these values, but in this case you got '^' which means to *not replace* them but all the rest although the '^' supposed to be inside the brackets (at least in Java it is).

Answer 6

^ is used to tell the regular expression engine(regex) that the match must start at the begining of the text.

so instead we type each character of the alphabet, we specify -a-z A-Z so that we'll both have uppercase and lowercase range.

Same with number, we can simply have a range 0-9 instead of writing all 10 digits.