regex find all the strings preceded by = and ending in &

Question

I need to find in a large body of text all the strings that are between = and & symbols. I don't want the result strings to contain = and &, only whats between them.

Answer 1

If your regex engine supports lookbehinds/lookaheads:

(?<==).*?(?=&)

Otherwise use this:

=(.*?)&

and catch capture group 1.

If your regex engine does not support non-greedy matching replace the .*? with [^&]*.

---

But as zzzzBov mentioned in a comment, if you're parsing GET URL prefixes there are usually better native methods for parsing GET arguments.

In PHP for example there would be:

<?php
$str = "first=value&arr[]=foo+bar&arr[]=baz";
parse_str($str);
echo $first;  // value
echo $arr[0]; // foo bar
echo $arr[1]; // baz
parse_str($str, $output);
echo $output['first'];  // value
echo $output['arr'][0]; // foo bar
echo $output['arr'][1]; // baz
?>

(As found on php.net.)

Edit: Appears you're using Javascript.

Javascript solution for parsing query string into object:

var queryString = {};
anchor.href.replace(
    new RegExp("([^?=&]+)(=([^&]*))?", "g"),
    function($0, $1, $2, $3) { queryString[$1] = $3; }
);

Source: http://stevenbenner.com/2010/03/javascript-regex-trick-parse-a-query-string-into-an-object/

Answer 2

Assuming your regex engine supports lookaheads.

/(?<==).*?(?=&)/

Edit :

Javascript doesn't support lookbehind so :

var myregexp = /=(.*?)(?=&)/g;
var match = myregexp.exec(subject);
while (match != null) {
    for (var i = 0; i < match.length; i++) {
        // matched text: match[i]
    }
    match = myregexp.exec(subject);
}

this is what you should use.

Explanation :

"
=       # Match the character “=” literally
(       # Match the regular expression below and capture its match into backreference number 1
   .       # Match any single character that is not a line break character
      *?      # Between zero and unlimited times, as few times as possible, expanding as needed (lazy)
)
(?=     # Assert that the regex below can be matched, starting at this position (positive lookahead)
   &       # Match the character “&” literally
)
"

Answer 3

/=([^&]*)&/

You'll of course need to adapt the syntax and what to do with it.