xslt-lab/site/content/xslt/functions/xpath-substring-before.md

title, description, date, version, versionLabel, category, syntax, tags

title	description	date	version	versionLabel	category	syntax	tags
substring-before()	Returns the part of a string that appears before the first occurrence of a given separator substring.	2026-04-18T00:00:00Z	1.0	XSLT 1.0	string function	substring-before(string, separator)	xslt reference xpath xslt1

Description

substring-before() finds the first occurrence of separator in string and returns everything that precedes it. If separator is not found, the function returns the empty string "". If separator is the empty string, the function also returns "".

Both arguments are converted to strings before processing. The search is case-sensitive.

substring-before() is the XPath 1.0 way to split a delimited string and extract the left-hand portion: usernames from user@host addresses, keys from key=value pairs, or path segments from URIs.

Parameters

Parameter	Type	Required	Description
string	xs:string	Yes	The string to search within.
separator	xs:string	Yes	The delimiter to search for.

Return value

xs:string — the portion of string before the first occurrence of separator, or "" if not found.

Examples

Extract username from an email address

Input XML:

<?xml version="1.0" encoding="UTF-8"?>
<users>
  <user email="alice@example.com"/>
  <user email="bob.smith@company.org"/>
</users>

Stylesheet:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="xml" indent="yes"/>

  <xsl:template match="/users">
    <usernames>
      <xsl:for-each select="user">
        <username><xsl:value-of select="substring-before(@email, '@')"/></username>
      </xsl:for-each>
    </usernames>
  </xsl:template>
</xsl:stylesheet>

Output:

<usernames>
  <username>alice</username>
  <username>bob.smith</username>
</usernames>

Extract key from a key=value pair

Input XML:

<?xml version="1.0" encoding="UTF-8"?>
<params>
  <param>color=blue</param>
  <param>size=large</param>
  <param>weight=1.5kg</param>
</params>

Stylesheet:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="xml" indent="yes"/>

  <xsl:template match="/params">
    <parsed>
      <xsl:for-each select="param">
        <entry>
          <key><xsl:value-of select="substring-before(., '=')"/></key>
          <value><xsl:value-of select="substring-after(., '=')"/></value>
        </entry>
      </xsl:for-each>
    </parsed>
  </xsl:template>
</xsl:stylesheet>

Output:

<parsed>
  <entry><key>color</key><value>blue</value></entry>
  <entry><key>size</key><value>large</value></entry>
  <entry><key>weight</key><value>1.5kg</value></entry>
</parsed>

Notes

• If separator does not appear in string, substring-before() returns "" — not the original string. Use contains() first if you need to distinguish the "not found" case.
• Only the first occurrence of separator is used. To split on the last occurrence, combine substring-before() with substring-after() and recursive templates or iterate with the translate() trick in XSLT 1.0.
• substring-before($s, '') returns "" as specified; this is a common source of confusion.
• In XSLT 2.0+, tokenize() provides a cleaner way to split strings on delimiters, including regex-based separators.

See also

• substring-after()
• starts-with()
• contains()
• substring()