Value-of select in <a href=> (XSLT) - xslt

Question

I try to concstruct link with
<xsl:element name="a">
<xsl:attribute name="href">
<xsl:value-of select="concat('file:///', substring-before('%RolesPath%', 'roles'),'Flores.chm')"/>
</xsl:attribute>
Help
</xsl:element>
but I get error:
File file:///Flores.chm not found
I'm pretty sure, that variable %RolesPath% works fine. I'm using it in code normally. And if I use in code only
<xsl:value-of select="concat('file:///', substring-before('%RolesPath%', 'roles'),'Flores.chm')"/>
I get
file:///C:\Flores\Flores.chm
which is right path. Where I'm doing mistake please?
edit. %RolesPath% stores path to specify folder of program, which works with this code. In my case %RolesPath% stores "C:\Flores\roles\".
To specify my problem. I need open file(Flores.chm) in root folder of program. Program can be install everywhere in PC and prapably only way, how I can get the path is via %RolesPath%.

Answer 1

What you are passing to substring-before() is just a string ('%RolesPath%'). It appears that you are trying to use a Windows environment variable. This isn't going to work the way you're using it.
I think you have 2 options:
Option 1
Pass the value of the environment variable as an xsl:param when you call the stylesheet. This would work in either XSLT 1.0 or 2.0.
You would need the xsl:param:
<xsl:param name="RolesPath"/>
and this is how you would reference it:
<a href="{concat('file:///', substring-before($RolesPath, 'roles'),'Flores.chm')}"/>
Option 2
Use the environment-variable() function. This would only work with an XSLT 3.0 processor, such as Saxon-PE or EE.
Example:
<a href="{concat('file:///', substring-before(environment-variable('RolesPath'), 'roles'),'Flores.chm')}"/>
Here's another example of environment-variable() to show the function actually working:
XSLT 3.0
<xsl:stylesheet version="3.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output indent="yes"/>
<xsl:strip-space elements="*"/>
<xsl:template match="/">
<environment-variable name="TEMP" value="{environment-variable('TEMP')}"/>
</xsl:template>
</xsl:stylesheet>
Output (when applied to any well-formed XML)
<environment-variable name="TEMP" value="C:\Users\dhaley\AppData\Local\Temp"/>

Answer 2

Use this shorter expression:
<a href="file:///{substring-before($RolesPath, 'roles')}Flores.chm"/>
where $RolesPath is passed as an external, global parameter to the transformation.
How exactly to pass an external parameter to the transformation varies from one XSLT processor to another -- read your XSLT processor documentation. Some XSLT processors also allow string-typed parameters to be passed to the transformation from a command-line execution utility.