Manual Chapter : Tcl Usage

Applies To:

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BIG-IP APM

  • 14.1.2, 14.1.0
Manual Chapter

Tcl Usage

About Tcl usage in APM

The Tcl programming language can be used for writing advanced branch rules in the visual policy editor, and for assigning variables to custom expressions in the Variable Assign action.
Use of Tcl is optional; it provides an alternative to using the expression builder (in the visual policy editor), and to using other options provided by the Variable Assign action.

Tcl syntax notes

Access Policy Manager (APM) supports standard Tcl syntax and additional commands and operators listed in the table.

Standard Tcl Syntax

APM supports the various facilities provided by the Tcl language; for example, loops (
while
,
foreach
, and so on), conditions (
ifelse
,
switch
, and so on), functions (
proc
), and built-in Tcl commands (
strings
,
split
, and so on), as well as various Tcl operators.

Additional commands and operators

In addition to standard Tcl syntax, APM supports these commands and operators:
  • mcget
    command
  • Rule operators: A rule operator compares two operands in an expression.
  • Logical operators: A logical operator compares two values in an expression.
iRules on the BIG-IP system can provide functionality to the BIG-IP system components. However, Tcl commands that are specific to iRules are not available in access policy rules.
Command or Operator
Type
Description
mcget
Command
mcget
is an abbreviation for: get the session variable from the memory cache. Access Policy Manager (APM) stores all session variables generated in a session in its memory cache. When evaluating a branch rule, APM accesses session variables from system memory using the Tcl command
mcget
.
contains
Rule operator
Tests whether one string contains another string.
ends
_with
Rule operator
Tests whether one string ends with another string.
equals
Rule operator
Tests whether one string equals another string.
matches
Rule operator
Tests whether one string matches another string.
matches_regex
Rule operator
Tests whether one string matches a regular expression.
starts_with
Rule operator
Tests whether one string starts_with another string.
switch
Rule operator
Evaluates one of several scripts, depending on a given value.
and
Logical operator
Performs a logical and comparison between two values.
not
Logical operator
Performs a logical not action on a value.
or
Logical operator
Performs a logical or comparison between two values.

Tcl examples

These tables describe the syntax elements for the Tcl examples.

Using mcget

[
mcget
{
session.ssl.cert.cn
} ]
Syntax element
Value
Description
Brackets
[ ]
The brackets [ ] that enclose the entire command are the Tcl notation for command evaluation.
Command name
mcget
This command gets the session variable from the memory cache.
Braces
{ }
Braces enclose the session variable.
Session variable name
session.ssl.cert.cn
Session variables that are generated during a session are stored in memory cache.

Checking a certificate field

expr
{ [
mcget
{
session.ssl.cert.OU
} ]contains "PD" }
This expression checks whether the Organizational Unit (OU) field of a user certificate contains the text PD.
Syntax element
Value
Description
Command name
expr
The Tcl language specifies that an expression begin with the syntax
expr
.
Rule operator
contains
This operator checks for the string PD.
Return values
0 or 1
0 usually indicates failure, while 1 usually indicates success.