Usually one reads or creates documents in the repository via 4Suite's XSLT extension elements & functions. But sometimes you really want to use the file system.
For writing documents to the file system, use the EXSLT 'document' extension element. The following is an example script that writes the current date to a file called "/tmp/foo.txt":
<?xml version="1.0"?>
<xsl:transform version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:exslt="http://exslt.org/common"
xmlns:edt="http://exslt.org/dates-and-times"
extension-element-prefixes="exslt"
>
<xsl:output method="text"/>
<xsl:variable name="dt" select="edt:date-time()"/>
<xsl:template match="/">
<exslt:document href="file:///tmp/foo.txt">
<xsl:value-of select="$dt"/>
</exslt:document>
<xsl:text>Document output to file:///tmp/foo.txt </xsl:text>
<xsl:text>Current date: </xsl:text><xsl:value-of select="$dt"/>
</xsl:template>
</xsl:transform>