---
title: cstr_escape
summary: null
url: >-
  https://www.fastly.com/documentation/reference/vcl/functions/strings/cstr-escape
---

```
STRING cstr_escape(STRING string)
```

**Available in:** all subroutines

Escapes bytes from a string using C-style escape sequences.

The escaping rules in priority order are as follows:

1. if the byte is the double quote (0x22), it is escaped as `\"`
   (backslash double quote)
2. if the byte is the backslash (0x5C), it is escaped as `\\`
   (double backslash)
3. if the byte is one of the following control characters, it is escaped
   as follows:

- `\b` (0x08, backspace)
- `\t` (0x09, horizontal tab)
- `\n` (0x0A, newline)
- `\v` (0x0B, vertical tab)
- `\r` (0x0D, carriage return)

4. if the byte is less than or equal to 0x1F, or it is greater or equal to 0x7F
   (in other words, a control character not explicitly listed above),
   it is escaped as `\xHH` where HH is the hexadecimal value of the byte
5. if none of the above matched, the byte is passed through as-is:
   for example `a` for 0x61

> **HINT:** If you are escaping JSON strings, use `json.escape()` instead.

This function is not prefixed with the `std.` namespace.

## Example

```vcl
# var.escaped is set to: city="london"
declare local var.escaped STRING;
set var.escaped = "city=%22" + cstr_escape(client.geo.city.ascii) + "%22";
```