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DirXML Variable Expansion
DirXML Variable Expansion

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!!! Overview
Here are some interesting details about [DirXML Variables] Expansion.
This is some excellent details that were provided by "-Father Ramon" in a thread in the user forums.
!! Within IDM
Surrounding [DirXML Variables] with "$" or "~" work quite differently, even though in many cases the results may be the same.
! __Surrounding__ with "$"
Surrounding with "$" happens at __runtime__ and so the [DirXML Variables] is evaluated in real time.
A single or double dollar sign is evaluated at __runtime__ time. That is, when the code is executed the values are evaluated and expanded.
The form of $ expansion is used everywhere else __but NOT [XPATH]__. The expression and requires both a leading and trailing $. It is similar to ~expansion in that it results in text replacement rather than a variable reference, but differs in 3 important ways:
* It works with [Local Variables] as well as [Global Configuration Variables].
* It happens at runtime instead of load time, which means that it is expanded dynamically every time it is executed.
* When performed in a regular expression field or replacement text field, it tries to apply escaping to the value such that all the of the meta-characters within it are considered to be literals.
I say try yo because it is a known issue that it does the escaping wrong and ends up replacing the meta-character with the equivalent of \u0000 (e.g. the null character) so you will always end up with a bogus expression if your variable contained literals. I've been trying to convince somebody in a position to do so that this needs to be fixed for about a year and a half now (and that the fix is trivial), but so far with no luck.
Even if it did work correctly, what this means is that using $ expansion always results in an expression that matches the literal value of the variable and can't be used to embed wildcards or other meta-characters.
The end result of that being that you can't construct regular expressions in local variables, and you have to use ~ expansion instead of $ expansion if you want to use a GCV as a regular expression. I think it would be a great enhancement if when they fix the escaping problem, they add some additional syntax to signal that you want to expand in a
regex without escaping, maybe something like $!variable!$.
! __Surrounding__ with "~"
Surrounding with "~" works at replaced at driver startup time which is policy __load time__ and replaces the text in-line before the policy is even parsed. This is as if the replacement text was part of the policy. This is essentially equivalent to C/C++ macro expansion of constants created with #define.
! __Leading__ with "$"
The leading "$" is used __only__ in [XPATH] Expressions.
Leading with a "$" in [XPATH] happens at __runtime__ and so the [DirXML Variables] is evaluated in real time.
A single or double dollar sign is evaluated at __runtime__ time. That is, when the code is executed the values are evaluated and expanded.
!! Variables in [XPATH]
The following can be used in [XPATH] Expressions:
* leading "$" is used __only__ in [XPATH] Expressions -
* Surrounding with "~" - Gets all the Child Nodes Values for ~abc~
* Surrounding with "~" with Quotes '~abc~' - Gets the string Value for ~abc~
A leading "$" is a [DirXML Variables] reference and is used on [Global Configuration Variables] and [Local Variables].
For example, if you have [Global Configuration Variables] abc that contains the string "xyz", then the expression:
{{{
$abc
results in the string "XYZ"
}}}
but the expression
{{{
~abc~
results in the expression
"xyz"
}}}
Surrounding with "~" works at replaced at driver startup time which is policy __load time__ and replaces the text before the policy is even parsed, so it is as if the replacement text was part of the policy.
which is shorthand for:
{{{
child::xyz
}}}
Which selects all the abc elements that are children of the context node.
To get a string from ~ expansion, you would need.
{{{
'~abc~'
which would expand to:
'xyz'
}}}
which is a string literal.
!! More Information
There might be more information for this subject on one of the following:
[{ReferringPagesPlugin before='*' after='\n' }]
This page (revision-1) was last changed on 29-Nov-2024 16:16 by UnknownAuthorTop