[xpath] How to select the first element with a specific attribute using XPath

The XPath bookstore/book[1] selects the first book node under bookstore.

How can I select the first node that matches a more complicated condition, e.g. the first node that matches /bookstore/book[@location='US']

    <bookstore>
     <book location="US">A1</book>
     <category>
      <book location="US">B1</book>
      <book location="FIN">B2</book>
     </category>
     <section>
      <book location="FIN">C1</book>
      <book location="US">C2</book>
     </section>
    </bookstore> 

So Given the above; you can select the first book with

(//book[@location='US'])[1]

And this will find the first one anywhere that has a location US. [A1]

//book[@location='US']

Would return the node set with all books with location US. [A1,B1,C2]

(//category/book[@location='US'])[1]

Would return the first book location US that exists in a category anywhere in the document. [B1]

(/bookstore//book[@location='US'])[1]

will return the first book with location US that exists anywhere under the root element bookstore; making the /bookstore part redundant really. [A1]

In direct answer:

/bookstore/book[@location='US'][1]

Will return you the first node for book element with location US that is under bookstore [A1]

Incidentally if you wanted, in this example to find the first US book that was not a direct child of bookstore:

(/bookstore/*//book[@location='US'])[1]

for ex.

<input b="demo">

And

(input[@b='demo'])[1]

The easiest way to find first english book node (in the whole document), taking under consideration more complicated structered xml file, like:

<bookstore>
 <category>
  <book location="US">A1</book>
  <book location="FIN">A2</book>
 </category>
 <category>
  <book location="FIN">B1</book>
  <book location="US">B2</book>
 </category>
</bookstore> 

is xpath expression:

/descendant::book[@location='US'][1]

As an explanation to Jonathan Fingland's answer:

• multiple conditions in the same predicate ([position()=1 and @location='US']) must be true as a whole
• multiple conditions in consecutive predicates ([position()=1][@location='US']) must be true one after another
• this implies that [position()=1][@location='US'] != [@location='US'][position()=1]
  while [position()=1 and @location='US'] == [@location='US' and position()=1]
• hint: a lone [position()=1] can be abbreviated to [1]

You can build complex expressions in predicates with the Boolean operators "and" and "or", and with the Boolean XPath functions not(), true() and false(). Plus you can wrap sub-expressions in parentheses.

Use the index to get desired node if xpath is complicated or more than one node present with same xpath.

Ex :

(//bookstore[@location = 'US'])[index]

You can give the number which node you want.

/bookstore/book[@location='US'][1] works only with simple structure.

Add a bit more structure and things break.

With-

<bookstore>
 <category>
  <book location="US">A1</book>
  <book location="FIN">A2</book>
 </category>
 <category>
  <book location="FIN">B1</book>
  <book location="US">B2</book>
 </category>
</bookstore> 

/bookstore/category/book[@location='US'][1] yields

<book location="US">A1</book>
<book location="US">B2</book>

not "the first node that matches a more complicated condition". /bookstore/category/book[@location='US'][2] returns nothing.

With parentheses you can get the result the original question was for:

(/bookstore/category/book[@location='US'])[1] gives

<book location="US">A1</book>

and (/bookstore/category/book[@location='US'])[2] works as expected.

With help of an online xpath tester I'm writing this answer...
For this:

<table id="t2"><tbody>
<tr><td>123</td><td>other</td></tr>
<tr><td>foo</td><td>columns</td></tr>
<tr><td>bar</td><td>are</td></tr>
<tr><td>xyz</td><td>ignored</td></tr>
</tbody></table>

the following xpath:

id("t2") / tbody / tr / td[1]

outputs:

123
foo
bar
xyz

Since 1 means select all td elements which are the first child of their own direct parent.
But the following xpath:

(id("t2") / tbody / tr / td)[1]

outputs:

123

if namespace is provided on the given xml, its better to use this.

(/*[local-name() ='bookstore']/*[local-name()='book'][@location='US'])[1]