Using
$("a").attr("href", "http://www.google.com/")
will modify the href of all hyperlinks to point to Google. You probably want a somewhat more refined selector though. For instance, if you have a mix of link source (hyperlink) and link target (a.k.a. "anchor") anchor tags:
<a name="MyLinks"></a>
<a href="http://www.codeproject.com/">The CodeProject</a>
...Then you probably don't want to accidentally add href attributes to them. For safety then, we can specify that our selector will only match <a> tags with an existing href attribute:
$("a[href]") //...
Of course, you'll probably have something more interesting in mind. If you want to match an anchor with a specific existing href, you might use something like this:
$("a[href='http://www.google.com/']").attr('href', 'http://www.live.com/')
This will find links where the href exactly matches the string http://www.google.com/. A more involved task might be matching, then updating only part of the href:
$("a[href^='http://stackoverflow.com']")
.each(function()
{
this.href = this.href.replace(/^http:\/\/beta\.stackoverflow\.com/,
"http://stackoverflow.com");
});
The first part selects only links where the href starts with http://stackoverflow.com. Then, a function is defined that uses a simple regular expression to replace this part of the URL with a new one. Note the flexibility this gives you - any sort of modification to the link could be done here.