注意： Opensips的版本为2.4.x
参考文献地址 https://www.opensips.org/Documentation/Script-CoreVar-2-4

变量语法

name

其实是“type”，因为它分为几种，

1. 标量/脚本变量var
2. 键值对avp （Attribute Value Pair）
3. 系统变量/伪变量PV (pseudo variables)
4. 转移字符串

subname

就是对应type的变量name

index

如果是avp和PV，可以储存多个值，这里就可以使用index来索引。注意，它支持负数，表述从后往前

transformation

就是对取出的value做变换，如截取长度，取子字符串等

context

主要是区别request和reply两个方向的，如果不清楚的话，可以参考学习笔记一

标量/脚本变量

下面是官网的例子

$var(a) = 2;  # sets the value of variable 'a' to integer '2'
$var(a) = "2";  # sets the value of variable 'a' to string '2'
$var(a) = 3 + (7&(~2)); # arithmetic and bitwise operation
$var(a) = "sip:" + $au + "@" + $fd; # compose a value from authentication username and From URI domain

# using a script variable for tests
if( [ $var(a) & 4 ] ) {
  xlog("var a has third bit set\n");
}

AVP变量

TM模块有个参数onreply_avp_mode，这个参数如果设置为0（默认为0），则AVP的生命周期只有request route，branch route以及failure route阶段，reply route阶段没有；但是有意思的是，此时，var的生命周期是整个dialog。
如果设置为1，AVP的生命周期会包含request route，branch route以及failure route阶段，reply route阶段。但是只有一个transaction内的所有阶段。新的transaction是没有继承的；此时，var的生命周期只有一个transactin的equest route，branch route阶段。

modparam("tm", "onreply_avp_mode", 1)

官网的例子

例子1， 跨route阶段保存值

# enable avps in onreply route
modparam("tm", "onreply_avp_mode", 1)
...
route{
...
$avp(tmp) = $Ts ; # store the current time (at request processing)
...
t_onreply("1");
t_relay();
...
}

onreply_route[1] {
    if (t_check_status("200")) {
        # calculate the setup time
        $var(setup_time) = $Ts - $avp(tmp);
    }
}

例子2 多值操作

$avp(17) = "one";
# we have a single value
$avp(17) = "two";
# we have two values ("two","one")
$avp(17) = "three";
# we have three values ("three","two","one")

xlog("accessing values with no index: $avp(17)\n");
# this will print the first value, which is the last added value -> "three"

xlog("accessing values with no index: $(avp(17)[2])\n");
# this will print the index 2 value (third one), -> "one"

# remove the last value of the avp; if there is only one value, the AVP itself will be destroyed
$avp(17) = NULL;

# delete all values and destroy the AVP
avp_delete("$avp(17)/g");

# delete the value located at a certain index 
$(avp(17)[1]) = NULL;

#overwrite the value at a certain index
$(avp(17)[0]) = "zero";

PV 系统变量