= Double Quoted Strings

.Syntax
`"string"`

A double-quoted string allows escape sequences and xref:xlat/index.adoc[dynamic
expansions]. As with xref:type/string/single.adoc[single-quoted strings], text
within double quotes can include spaces.

The main difference between the single and double quoted strings is
that the double quoted strings can be dynamically expanded. The syntax
`${...}` is used for parse-time expansion and `%{...}` is used for
run-time expansion. The difference between the two methods is that the
`${...}` form is expanded when the server loads the configuration
files and is valid anywhere in the configuration files. The `%{...}`
xref:xlat/index.adoc[string expansion] form is valid only in conditional
expressions and attribute assignments.

The output of the dynamic expansion can be interpreted as a string,
a number, or an IP address, depending on its context.

Note that the interpretation of text _strongly_ depends on the
context.  The text `"0000"` can be interpreted as a data type
"integer", having value zero, or a data type "string", having value
`"0000"`.  In general when a particular piece of text is used, it is
used with the context of a known attribute.  That attribute has a
xref:type/index.adoc[data type], and the text will be interpreted as that
data type.

NOTE: Most values retrieved from external datastores will be treated implicitly
as double-quoted strings.

== Escape sequences

Escape sequences allow the inclusion of characters that may be difficult to
represent in datastores, or the FreeRADIUS configuration files.

.Escape sequences and their descriptions
[options="header", cols="15%,85%"]
|=====
| Escape sequence     | Character represented
| `\\`                | Literal backslash (0x5c)
| `\r`                | Carriage return (0x0d)
| `\n`                | Line feed (0x0a)
| `\t`                | Horizontal tab (0x09)
| `\"`                | Double quote (0x22)
| `\x<hex><hex>`      | A byte whose numerical value is given by `<hex><hex>` interpreted as a hexadecimal number.
| `\x<oct><oct><oct>` | A byte whose numerical value is given by `<oct><oct><oct>` interpreted as an octal number.
|=====

.Examples

`"word"` +
`"a string"' +
`"foo\"bar\""` +
`"this is a long string"` +
`"this has embedded\ncharacters"` +
`"attribute\tvalue\nusername\t%{User-Name}\nreply-message\t%{reply.Reply-Message}"`
`"The result of 'SELECT * FROM foo WHERE 1' is: %{sql:SELECT * FROM foo WHERE 1}"`

// Licenced under CC-by-NC 4.0.
// Copyright (C) 2019 Arran Cudbard-Bell <a.cudbardb@freeradius.org>
// Copyright (C) 2019 The FreeRADIUS project.
// Copyright (C) 2020 Network RADIUS SAS.