Double Quoted Strings

Syntax

"string"

A double-quoted string allows escape sequences and dynamic expansions. As with 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 %{…} dynamic 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 data type, and the text will be interpreted as that data type.

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.

Table 1. Escape sequences and their descriptions
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.

Methods of Creating Strings

There are a few different ways in which double-quoted strings can be created. The simplest is just an in-line string, as in "string". However, strings can also be created via expressions. and dynamic expansions.

In general, creating strings via dynamic expansions will result in the printed version of the expansion being used.

Example of double-quoted string expansion

"User-Name is %{User-Name}"
"IP Address is %{reply.Framed-IP-Address}

Both of the above expansions will return the printed version of the expansion. For User-Name, it will be the string version of the users name, as would be expected. However, for the Framed-IP-Address example, the printed version will be an ASCII string such as 192.0.2.1, even though the actual IP address is a 32-bit number.

When a string is created via an expression using the + operator, the resulting string can be quite different, depending on the inputs.

Example of casting to 'string'

"User-Name is " + &User-Name
"IP Address is " + (string) &reply.Framed-IP-Address

The output strings here (with casting) are the same as for the previous example. Note that we do not have to cast &User-Name, because it is already a string.

Example of casting to 'octets'

"User-Name is " + (octets) &User-Name
"IP Address is " + (octets) &reply.Framed-IP-Address

The output strings here are completely different than for the previous examples. The output data type is octets, and not string.

If the goal is to have the raw octets data inserted into a string, you must cast the octets to a string value. That process will copy the input octets value to a the output, changing the data type to string. The value is left alone.

Example of casting to raw 'octets'

"User-Name is %{Tmp-Octets-0}"
"User-Name is %{(string) &Tmp-Octets-0}"

if the &Tmp-Octets-0 attribute has value 0x666f6f (foo)

In the first expansion, the resulting output is User-Name is 0x666f6f. In the second expansion, the resulting output is User-name is foo.

Note that placing raw octets data into a string may allow for binary data to be inserted into what should be a printable string. Any uses of the string will result in the non-printable data being escaped as \000 or other methods such a \n, depending on how and wheere the string is being used.

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}"