373 lines
13 KiB
Markdown
373 lines
13 KiB
Markdown
---
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title: Xpath
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category: HTML
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layout: default-ad
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tags: [Featured]
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---
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### Descendant selectors
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| CSS | Xpath | ? |
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| ---- | ---- | -- |
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| `h1` | `//h1` | [?](#prefixes) |
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| `div p` | `//div//p` | [?](#axes) |
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| `ul > li` | `//ul/li` | [?](#axes) |
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| `ul > li > a` | `//ul/li/a` | |
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| `div > *` | `//div/*` | |
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| ---- | ---- | -- |
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| `:root` | `/` | [?](#prefixes) |
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| `:root > body` | `/body` | |
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{:.greycode.no-head.xp}
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### Attribute selectors
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| CSS | Xpath | ? |
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| ---- | ---- | -- |
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| `#id` | `//[@id="id"]` | [?](#predicates) |
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| `.class` | `//[@class="class"]` *...[kinda](#class-check)* | |
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| `input[type="submit"]` | `//input[@type="submit"]` | |
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| `a#abc[for="xyz"]` | `//a[@id="abc"][@for="xyz"]` | [?](#chaining-order) |
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| `a[rel]` | `//a[@rel]` | |
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| ---- | ---- | -- |
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| `a[href^='/']` | `//a[starts-with(@href, '/')]` | [?](#string-functions) |
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| `a[href$='pdf']` | `//a[ends-with(@href, '.pdf')]` | |
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| `a[href~='://']` | `//a[contains(@href, '://')]` *...[kinda](#class-check)* | |
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{:.greycode.no-head.xp}
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### Order selectors
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| CSS | Xpath | ? |
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| ---- | ---- | -- |
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| `ul > li:first-child` | `//ul/li[1]` | [?](#indexing) |
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| `ul > li:nth-child(2)` | `//ul/li[2]` | |
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| `ul > li:last-child` | `//ul/li[last()]` | |
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| `li#id:first-child` | `//li[@id="id"][1]` | |
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| `a:first-child` | `//a[1]` | |
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| `a:last-child` | `//a[last()]` | |
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{:.greycode.no-head.xp}
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### Siblings
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| CSS | Xpath | ? |
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| ---- | ---- | -- |
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| `h1 ~ ul` | `//h1/following-sibling::ul` | [?](#using-axes) |
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| `h1 + ul` | `//h1/following-sibling::ul[1]` | |
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| `h1 ~ #id` | `//h1/following-sibling::[@id="id"]` | |
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{:.greycode.no-head.xp}
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### jQuery
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| CSS | Xpath | ? |
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| ---- | ---- | -- |
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| `$('ul > li').parent()` | `//ul/li/..` | [?](#other-axes) |
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| `$('li').closest('section')` | `//li/ancestor-or-self::section` | |
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| `$('a').attr('href')` | `//a/@href` | [?](#steps) |
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| `$('span').text()` | `//span/text()` | |
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{:.greycode.no-head.xp}
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### Other things
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| CSS | Xpath | ? |
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| ---- | ---- | -- |
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| `h1:not([id])` | `//h1[not(@id)]` | [?](#boolean-functions) |
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| Text match | `//button[text()="Submit"]` | [?](#operators) |
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| Text match (substring) | `//button[contains(text(),"Go")]` | |
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| Arithmetic | `//product[@price > 2.50]` | |
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| Has children | `//ul[*]` | |
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| Has children (specific) | `//ul[li]` | |
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| Or logic | `//a[@name or @href]` | [?](#operators) |
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| Union (joins results) | `//a | //div` | [?](#unions) |
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{:.greycode.no-head.xp}
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<style>
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/* ensure tables align */
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table.xp {table-layout: fixed;}
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table.xp tr>:nth-child(1) {width: 30%;}
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table.xp tr>:nth-child(2) {width: auto;}
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table.xp tr>:nth-child(3) {width: 10%; text-align:right;}
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</style>
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### Class check
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Xpath doesn't have the "check if part of space-separated list" operator, so this is the workaround ([source](http://pivotallabs.com/xpath-css-class-matching/)):
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```sh
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//div[contains(concat(' ',normalize-space(@class),' '),' foobar ')]
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```
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{:.light}
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Expressions
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-----------
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### Prefixes
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Begin your expression with any of these.
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| Prefix | Example |
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| --- | --- |
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| `//` *anywhere* | `//hr[@class='edge']` |
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| `./` *relative* | `./a` |
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| `/` *root* | `/html/body/div` |
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{:.greycode.no-head}
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### Axes
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Separate your steps with `/`. Use two (`//`) if you don't want to select direct children.
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| Axis | Example |
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| --- | --- |
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| `/` *child* | `//ul/li/a` |
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| `//` *descendant* | `//[@id="list"]//a` |
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{:.greycode.no-head}
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### Steps
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A step may have an element name (`div`) and [predicates](#predicate) (`[...]`). Both are optional.
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```sh
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//div
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//div[@name='box']
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//[@id='link']
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```
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{:.light}
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They can also be these other things.
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```sh
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//a/text() #=> "Go home"
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//a/@href #=> "index.html"
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//a/* #=> All a's child elements
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```
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Predicates
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----------
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### Predicates (`[...]`)
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Restricts a nodeset only if some condition is true. They can be chained.
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```sh
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//div[true()]
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//div[@class="head"]
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//div[@class="head"][@id="top"]
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```
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{:.light}
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### Operators
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Use comparison and logic operators to make conditionals.
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```sh
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# Comparison
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//a[@id = "xyz"]
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//a[@id != "xyz"]
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//a[@price > 25]
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```
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```sh
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# Logic (and/or)
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//div[@id="head" and position()=2]
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//div[(x and y) or not(z)]
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```
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### Using nodes
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You can use nodes inside predicates.
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```sh
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# Use them inside functions
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//ul[count(li) > 2]
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//ul[count(li[@class='hide']) > 0]
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```
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```sh
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# This returns `<ul>` that has a `<li>` child
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//ul[li]
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```
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### Indexing
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Use `[]` with a number, or `last()` or `position()`.
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```sh
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//a[1] # first <a>
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//a[last()] # last <a>
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//ol/li[2] # second <li>
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//ol/li[position()=2] # same as above
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//ol/li[position()>1] # :not(:first-child)
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```
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### Chaining order
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Order is significant, these two are different.
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```sh
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a[1][@href='/']
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a[@href='/'][1]
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```
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### Nesting predicates
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This returns `<section>` if it has an `<h1>` descendant with `id='hi'`.
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```
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//section[//h1[@id='hi']]
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```
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Functions
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---------
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### Node functions
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```sh
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name() # //[starts-with(name(), 'h')]
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text() # //button[text()="Submit"]
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# //button/text()
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lang(str)
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namespace-uri()
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count() # //table[count(tr)=1]
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position() # //ol/li[position()=2]
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```
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### Boolean functions
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```sh
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not(expr) # button[not(starts-with(text(),"Submit"))]
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```
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### String functions
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```sh
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contains() # font[contains(@class,"head")]
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starts-with() # font[starts-with(@class,"head")]
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ends-with() # font[ends-with(@class,"head")]
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concat(x,y)
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substring(str, start, len)
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substring-before("01/02", "/") #=> 01
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substring-after("01/02", "/") #=> 02
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translate()
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normalize-space()
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string-length()
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```
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### Type conversion
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```sh
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string()
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number()
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boolean()
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```
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Axes
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----
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### Using axes
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Steps of an expression are separated by `/`, usually used to pick child nodes. That's not always true: you can specify a different "axis" with `::`.
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```sh
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//ul/li # ul > li
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//ul/child::li # ul > li (same)
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//ul/following-sibling::li # ul ~ li
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//ul/descendant-or-self::li # ul li
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//ul/ancestor-or-self::li # $('ul').closest('li')
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```
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{:.light}
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### Child axis
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This is the default axis. This makes `//a/b/c` work.
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```sh
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# both the same
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//ul/li/a
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//child::ul/child::li/child::a
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```
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```sh
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# both the same
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# this works because `child::li` is truthy, so the predicate succeeds
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//ul[li]
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//ul[child::li]
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```
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```sh
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# both the same
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//ul[count(li) > 2]
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//ul[count(child::li) > 2]
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```
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### Descendant-or-self axis
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`//` is short for the `descendant-or-self::` axis.
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```sh
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# both the same
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//div//h4
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//div/descendant-or-self::h4
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```
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```sh
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# both the same
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//ul//[last()]
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//ul/descendant-or-self::[last()]
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```
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### Other axes
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There are other axes you can use.
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| Axis | Abbrev | Description |
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| --- | --- | --- |
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| `ancestor` | | |
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| `ancestor-or-self` | | |
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| --- | --- | --- |
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| `attribute` | `@` | `@href` is short for `attribute::href` |
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| `child` | | `div` is short for `child::div` |
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| `descendant` | | |
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| `descendant-or-self` | `//` | `//` is short for `/descendant-or-self::node()/` |
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| `namespace` | | |
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| --- | --- | --- |
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| `self` | `.` | `.` is short for `self::node()` |
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| `parent` | `..` | `..` is short for `parent::node()` |
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| --- | --- | --- |
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| `following` | | |
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| `following-sibling` | | |
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| `preceding` | | |
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| `preceding-sibling` | | |
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{:.greycode}
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### Unions
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Use `|` to join two expressions.
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```sh
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//a | //span
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```
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More examples
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-------------
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```sh
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//* # all elements
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count(//*) # count all elements
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(//h1)[1]/text() # text of the first h1 heading
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//li[span] # find a <li> with an <span> inside it
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# ...expands to //li[child::span]
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//ul/li/.. # use .. to select a parent
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```
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```sh
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# Find a <section> that directly contains h1#section-name
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//section[h1[@id='section-name']]
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```
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```sh
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# Find a <section> that contains h1#section-name
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# (Same as above, but use descendant-or-self instead of child)
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//section[//*[@id='section-name']]
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```
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```sh
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# like jQuery's $().closest('.box')
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./ancestor-or-self::[@class="box"]
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```
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```sh
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# Find <item> and check its attributes
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//item[@price > 2*@discount]
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```
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References
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----------
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* [Xpath test bed](http://www.whitebeam.org/library/guide/TechNotes/xpathtestbed.rhtm) (whitebeam.org)
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