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=== Scripting

In the console section of the users guide, we introduced the scripting support.

==== Assignation

You already know the first usage of scripting: execution of command.

----
karaf@root()> echo hello world
hello world
----

You can also assign value to session variables:

----
karaf@root()> msg = "hello world"
hello world
----

Once you have assigned a value to a variable, you can display this value using the "resolved" variable name:

----
karaf@root()> echo $msg
hello world
----

The () are execution quotes (like the backquotes when you use bash on Unix).

----
karaf@root()> ($.context bundle 1) location
mvn:org.apache.karaf.jaas/org.apache.karaf.jaas.modules/4.0.0
----

The `$.context` access the context variables in the current session.
We access to the `bundle` variable (an array containing all bundles), and we want to display the bundle location for
the bundle at the index 1 in the bundle array.

==== Expressions

The shell has a built-in expression parser.  Expressions must be enclosed with the `%(...)` syntax.

Examples:

----
karaf@root()> %(1+2)
3
karaf@root()> a = 0
0
karaf@root()> %(a+=1)
1
karaf@root()> %(a+=1)
2
karaf@root()> b=1
1
karaf@root()> %(SQRT(a^2 + b^2))
1.7320508
----

===== Mathematical Operators

|===
|Operator |Description

|+
| Additive operator

|-
| Subtraction operator

|*
| Multiplication operator

|/
| Division operator

|%
| Remainder operator (Modulo)

|^
| Power operator
|===

===== Boolean Operators

|===
|Operator |Description

|=
| Equals

|==
| Equals

|!=
|Not equals

|<>
| Not equals

|<
| Less than

|<=
| Less than or equal to

|>
| Greater than

|>=
| Greater than or equal to

|&&
| Boolean and

|\|\|
|Boolean or
|===

===== Supported Functions

|===
|Function |Description

|NOT(_expression_)
|Boolean negation, 1 (means true) if the expression is not zero

|IF(_condition_,_value_if_true_,_value_if_false_)
|Returns one value if the condition evaluates to true or the other if it evaluates to false

|RANDOM()
|Produces a random number between 0 and 1

|MIN(_e1_,_e2_)
|Returns the smaller of both expressions

|MAX(_e1_,_e2_)
|Returns the bigger of both expressions

|ABS(_expression_)
|Returns the absolute (non-negative) value of the expression

|ROUND(_expression_,precision)
|Rounds a value to a certain number of digits, uses the current rounding mode

|FLOOR(_expression_)
|Rounds the value down to the nearest integer

|CEILING(_expression_)
|Rounds the value up to the nearest integer

|LOG(_expression_)
|Returns the natural logarithm (base e) of an expression

|SQRT(_expression_)
|Returns the square root of an expression

|SIN(_expression_)
|Returns the trigonometric sine of an angle (in degrees)

|COS(_expression_)
|Returns the trigonometric cosine of an angle (in degrees)

|TAN(_expression_)
|Returns the trigonometric tangens of an angle (in degrees)

|SINH(_expression_)
|Returns the hyperbolic sine of a value

|COSH(_expression_)
|Returns the hyperbolic cosine of a value

|TANH(_expression_)
|Returns the hyperbolic tangens of a value

|RAD(_expression_)
|Converts an angle measured in degrees to an approximately equivalent angle measured in radians

|DEG(_expression_)
|Converts an angle measured in radians to an approximately equivalent angle measured in degrees
|===

Functions names are case insensitive.

===== Supported Constants

|===
|Constant |Description

|PI
|The value of _PI_, exact to 100 digits

|TRUE
|The value one

|FALSE
|The value zero
|===

==== List, maps, pipes and closures

Using [], you can define array variable:

----
karaf@root()> list = [1 2 a b]
1
2
a
b

----

You can also create a map if you put variables assignation in the array:

----
karaf@root()> map = [Jan=1 Feb=2 Mar=3]
Jan                 1
Feb                 2
Mar                 3
----

Using the | character, you can pipe output from a command as an input to another one.

For instance, you can access to the bundles context variables and send it as input to the grep command:

----
karaf@root()> ($.context bundles) | grep -i felix
    0|Active     |    0|org.apache.felix.framework (4.2.1)
   21|Active     |   11|org.apache.felix.fileinstall (3.2.6)
   43|Active     |   10|org.apache.felix.configadmin (1.6.0)
   51|Active     |   30|org.apache.felix.gogo.runtime (0.10.0)
----

You can assign name to script execution. It's what we use for alias:

----
karaf@root()> echo2 = { echo xxx $args yyy }
echo xxx $args yyy
karaf@root()> echo2 hello world
xxx hello world yyy
----

==== Startup

The `etc/shell.init.script` file is executed at startup in each shell session, allowing the definition of additional
variables or aliases or even complex functions. It's like the bashrc or profile on Unix.

==== Constants and variables

Apache Karaf console provides a set of implicit constants and variables that you can use in your script.

* `$.context` to access a bundle context
* `$.variables` to access the list of defined variables
* `$.commands` to access the list of defined commands

The variables starting with a # that are defined as Function (such as closures) will be executed automatically:

----
karaf@root> \#inc = { var = "${var}i" ; $var }
var = "${var}i" ; $var
karaf@root> echo $inc
i
karaf@root> echo $inc
ii
karaf@root>
----

==== Built-in variables and commands

Apache Karaf console provides built-in variable very useful for scripting:

* `$args` retrieves the list of script parameters, given to the closure being executed
* `$1 .. $999` retrieves the nth argument of the closure
* `$it` (same as `$1`) is used in a loop to access the current iterator value

Apache Karaf console provides commands for scripting:

* `shell:if`
* `shell:new`
* `shell:each`
* ...

See the link:commands[full list of `shell` commands] for details.

==== Leveraging existing Java capabilities (via reflection)

Apache Karaf console supports loading and execution of Java classes.

The `$karaf.lastException` implicit variable contains the latest Exception thrown.

----
karaf@root()> ($.context bundle) loadClass foo
Error executing command: foo not found by org.apache.karaf.shell.console [17]
karaf@root()> $karaf.lastException printStackTrace
java.lang.ClassNotFoundException: foo not found by org.apache.karaf.shell.console [17]
	at org.apache.felix.framework.BundleWiringImpl.findClassOrResourceByDelegation(BundleWiringImpl.java:1460)
	at org.apache.felix.framework.BundleWiringImpl.access$400(BundleWiringImpl.java:72)
	at org.apache.felix.framework.BundleWiringImpl$BundleClassLoader.loadClass(BundleWiringImpl.java:1843)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
	at org.apache.felix.framework.Felix.loadBundleClass(Felix.java:1723)
	at org.apache.felix.framework.BundleImpl.loadClass(BundleImpl.java:926)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at org.apache.felix.gogo.runtime.Reflective.invoke(Reflective.java:137)
	at org.apache.felix.gogo.runtime.Closure.executeMethod(Closure.java:527)
	at org.apache.felix.gogo.runtime.Closure.executeStatement(Closure.java:403)
	at org.apache.felix.gogo.runtime.Pipe.run(Pipe.java:108)
	at org.apache.felix.gogo.runtime.Closure.execute(Closure.java:183)
	at org.apache.felix.gogo.runtime.Closure.execute(Closure.java:120)
	at org.apache.felix.gogo.runtime.CommandSessionImpl.execute(CommandSessionImpl.java:89)
	at org.apache.karaf.shell.console.jline.Console.run(Console.java:166)
	at java.lang.Thread.run(Thread.java:680)
----

It's possible to create objects to create commands "on the fly":

----
karaf@root()> addcommand system (($.context bundle) loadClass java.lang.System)
karaf@root()> system:getproperty karaf.name
root
----

It means that you can create object using the `new` directive, and call methods on the objects:

----
karaf@root> map = (new java.util.HashMap)
karaf@root> $map put 0 0
karaf@root> $map
0                   0
----

==== Examples

The following examples show some scripts defined in `etc/shell.init.script`.

The first example show a script to add a value into a configuration list:

----
#
# Add a value at the end of a property in the given OSGi configuration
#
# For example:
# > config-add-to-list org.ops4j.pax.url.mvn org.ops4j.pax.url.mvn.repositories http://scala-tools.org/repo-releases
#
config-add-to-list = {
  config:edit $1 ;
  a = (config:property-list | grep --color never $2 | tac) ;
  b = (echo $a | grep --color never "\b$3\b" | tac) ;
  if { ($b trim) isEmpty } {
    if { $a isEmpty } {
      config:property-set $2 $3
    } {
      config:property-append $2 ", $3"
    } ;
    config:update
  } {
    config:cancel
  }
}
----

This second example shows a script to wait for an OSGi service, up to a given timeout, and combine this script in
other scripts:

----
#
# Wait for the given OSGi service to be available
#
wait-for-service-timeout = {
  _filter = $.context createFilter $1 ;
  _tracker = shell:new org.osgi.util.tracker.ServiceTracker $.context $_filter null ;
  $_tracker open ;
  _service = $_tracker waitForService $2 ;
  $_tracker close
}
#
# Wait for the given OSGi service to be available with a timeout of 10 seconds
#
wait-for-service = {
  wait-for-service-timeout $1 10000
}
#
# Wait for the given command to be available with a timeout of 10 seconds
# For example:
# > wait-for-command dev watch
#
wait-for-command = {
  wait-for-service "(&(objectClass=org.apache.felix.service.command.Function)(osgi.command.scope=$1)(osgi.command.function=$2))"
}
----