Question

Can someone please tell me how the following regex resolves? I am trying to upload an app to Appspot, and am getting an error that my name does not meet the following criteria:

^(?:[a-z\d\-]{1,100}\~)?(?:(?!\-)[a-z\d\-\.]{1,100}:)?(?!-)[a-z\d\-]{1,100}$

Answer 1

Pretty complex, but I’ll try and boil the rules down to English.

1. There is only one tilde (~) allowed in the name, but it is optional. If there is a tilde, it must not be the first character in the name, it must have at least 1 and at most 100 letters, numbers or dashes in front of it.

2. There is only one colon (:) allowed in the name, and it is optional. If there is a colon, it must:

   a. come after the tilde, if present.

   b. come after 1 or more letters, numbers, dashes or full stops.

   c. the group of letters, numbers, dashes and full stops cannot start with a dash.

3. The rest of the name can contain any letter, number or dashes, up to a hundred characters. The optional tilde and colon sections must come before it, and it cannot start with a dash. You must use at least one character, and at most 100.

Some examples that are allowed:

• foo~bar.baz:spam-eggs

• something:other-

• whomever~thought-this-was-a-good-idea

• together.we.stand:strong

• simply-should-work

• -starting-dash~as.long.as.there.is.a:tilde-after-it

Some examples that won’t be allowed:

• -no-starting-dash

• -no-starting-dash:with-a-colon-but-no-tilde

• no.full.stops.without.a.colon.after.it

• ~no-tilde-at-the-start

• :no-colon-at-the-start

• more~than~one:tilde:or:colon