Regex \\s understanding

Question

I m trying to understand Json schema definition of below snippet,

  "translated_string": {
    "description": "A translated string",
    "type": "string",
    "minLength": 1,
    "not": {
      "type": "string",
      "pattern": "^\\s+$"
    }
  },

Questions:

what does \\s represents.
some explanation of snippet by giving some examples valid schema.

`\\s` represents an [escaped](https://stackoverflow.com/a/17597400/4607733) space metacharacter (see [Shorthand Character Classes](http://www.regular-expressions.info/shorthand.html)). What can't you understand about the snippet? — logi-kal, Jun 22 '17 at 12:42
@horcrux some explanation of snippet by giving some examples for valid schemas and not valid schemas — Arun G, Jun 22 '17 at 12:54
"^\\s+$" is "Any non empty string that is only whitespace", but the validator is taking the NOT of that (so anything BUT that) — Tezra, Jun 22 '17 at 12:58

score 3 · Answer 1 · answered Jun 22 '17 at 13:15

In regex syntax, \s is a metacharacter representing a whitespace (see Shorthand Character Classes). In some languages you need to double escape it because of the slash (so \\s).

Lets analyze the regex:

^ is the begin of the string
\\s is the space
+ is an operator meaning "one or more"
$ is the end of the string

So the pattern matches the strings composed only of at least one space and nothing more.

Let's now analyze the snippet:

"description" is just the description associated to the translated_string property
"type": "string" means that in the JSON you can only use a string value for the translated_string property
"not" means that the following is not permitted:
- "pattern": "^\\s+$" is the regex above (so it must not be matched)

Note that the snippet is equivalent to:

"translated_string": {
  "description": "A translated string",
  "type": "string",
  "not": {
    "type": "string",
    "pattern": "^\\s*$"
  }
},

(where the * operator means "zero or more")
or even simplier:

"translated_string": {
  "description": "A translated string",
  "type": "string",
  "pattern": "^\\S+$"
},

(where \\S is anything but a space)

So, the following JSON are correct:

"translated_string": "l"
"translated_string": " l"
"translated_string": " l "
"translated_string": "  l "

While the following JSON are not correct:

"translated_string": ""
"translated_string": " "
"translated_string": "  "
"translated_string": 1
"translated_string": [ SOMETHING ]
"translated_string": { SOMETHING }

Regex \\s understanding

1 Answers1