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Full coverage of XSLT 1.0, 2.0 and 3.0 elements and XPath functions: - 59 XSLT elements (xsl:stylesheet → xsl:use-accumulators) - 170 XPath functions (1.0 node/string/numeric/boolean, 2.0 sequence/ date/QName/string, 3.0 HOF/map/array/JSON/streaming) Each page: description, parameters table, return value, 2 runnable Saxon examples with input XML + stylesheet + output, notes, cross-links. xsltCompletions.js: all 229 entries now have blogSlug for hover links. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
121 lines
3.7 KiB
Markdown
121 lines
3.7 KiB
Markdown
---
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title: "substring-before()"
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description: "Returns the part of a string that appears before the first occurrence of a given separator substring."
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date: 2026-04-18T00:00:00Z
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version: "1.0"
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versionLabel: "XSLT 1.0"
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category: "string function"
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syntax: "substring-before(string, separator)"
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tags: ["xslt", "reference", "xpath", "xslt1"]
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---
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## Description
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`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 `""`.
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Both arguments are converted to strings before processing. The search is case-sensitive.
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`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.
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## Parameters
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| Parameter | Type | Required | Description |
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|-----------|------|----------|-------------|
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| `string` | xs:string | Yes | The string to search within. |
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| `separator` | xs:string | Yes | The delimiter to search for. |
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## Return value
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`xs:string` — the portion of `string` before the first occurrence of `separator`, or `""` if not found.
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## Examples
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### Extract username from an email address
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**Input XML:**
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```xml
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<?xml version="1.0" encoding="UTF-8"?>
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<users>
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<user email="alice@example.com"/>
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<user email="bob.smith@company.org"/>
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</users>
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```
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**Stylesheet:**
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```xml
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<?xml version="1.0" encoding="UTF-8"?>
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<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
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<xsl:output method="xml" indent="yes"/>
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<xsl:template match="/users">
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<usernames>
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<xsl:for-each select="user">
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<username><xsl:value-of select="substring-before(@email, '@')"/></username>
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</xsl:for-each>
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</usernames>
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</xsl:template>
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</xsl:stylesheet>
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```
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**Output:**
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```xml
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<usernames>
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<username>alice</username>
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<username>bob.smith</username>
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</usernames>
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```
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### Extract key from a key=value pair
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**Input XML:**
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```xml
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<?xml version="1.0" encoding="UTF-8"?>
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<params>
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<param>color=blue</param>
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<param>size=large</param>
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<param>weight=1.5kg</param>
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</params>
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```
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**Stylesheet:**
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```xml
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<?xml version="1.0" encoding="UTF-8"?>
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<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
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<xsl:output method="xml" indent="yes"/>
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<xsl:template match="/params">
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<parsed>
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<xsl:for-each select="param">
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<entry>
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<key><xsl:value-of select="substring-before(., '=')"/></key>
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<value><xsl:value-of select="substring-after(., '=')"/></value>
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</entry>
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</xsl:for-each>
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</parsed>
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</xsl:template>
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</xsl:stylesheet>
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```
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**Output:**
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```xml
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<parsed>
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<entry><key>color</key><value>blue</value></entry>
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<entry><key>size</key><value>large</value></entry>
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<entry><key>weight</key><value>1.5kg</value></entry>
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</parsed>
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```
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## Notes
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- 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.
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- 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.
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- `substring-before($s, '')` returns `""` as specified; this is a common source of confusion.
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- In XSLT 2.0+, `tokenize()` provides a cleaner way to split strings on delimiters, including regex-based separators.
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## See also
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- [substring-after()](../xpath-substring-after)
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- [starts-with()](../xpath-starts-with)
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- [contains()](../xpath-contains)
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- [substring()](../xpath-substring)
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