Regex Search: How can I make sure that the next character is not a backslash?

[isxtn]

I am trying to dig through some records and trying to get the q (query) from the raw data, but I keep getting data back that includes a backslash after the requested field (mostly as a unicode character representation, /u0026 which is an &).

For example, I have this search query to capture the page from which a search is being made (i.e., "location"): 

index="xxxx-data" | regex query="location=([a-zA-Z0-9_]+)+[^&]+" | rex field=_raw "location=(?<location>[a-zA-Z0-9%-]+).*" | rex field=_raw "q=(?<q>[a-zA-Z0-9%-_&+/]+).*"| table location,q

Which mostly works viewing the Statistics tab, except that it occasionally returns the next URL parameter, i.e.,

location	q
home_page	hello+world   // this is ok
about_page	goodbye+cruel+world\u0026anotherparam=anotherval    // not ok

 The second result should just be goodbye+cruel+world without the following parameter.

I have tried adding variations on regex NOT [^\\] for a backslash character but everything I've tried has either resulted in an error of the final bracket being escaped, or the backslash character ignored like so:

rex field=_raw  ...

regex attempt	result
"q=(?<q>[a-zA-Z0-9%-_&+/]+[^\\\]).*"	goodbye+cruel+world\u0026param=val
"q=(?<q>[a-zA-Z0-9%-_&+/]+[^\\]).*"	Error in 'rex' command: Encountered the following error while compiling the regex 'q=(?<q>[a-zA-Z0-9%-_&+/]+[^\]).*': Regex: missing terminating ] for character class.
"q=(?<q>[a-zA-Z0-9%-_&+/]+[^\]).*"	Error in 'rex' command: Encountered the following error while compiling the regex 'q=(?<q>[a-zA-Z0-9%-_&+/]+[^\]).*': Regex: missing terminating ] for character class.
"q=(?<q>[a-zA-Z0-9%-_&+/]+[^\\u0026]).*"	Error in 'rex' command: Encountered the following error while compiling the regex 'q=(?<q>[a-zA-Z0-9%-_&+/]+[^\u0026]).*': Regex: PCRE does not support \L, \l, \N{name}, \U, or \u.
"q=(?<q>[a-zA-Z0-9%-_&+/]+[^u0026]).*"	goodbye+cruel+world\u0026param=val"
"q=(?<q>[a-zA-Z0-9%-_&+/]+[^&]).*"	goodbye+cruel+world\u0026param=val"
"q=(?<q>[a-zA-Z0-9%-_&+/]+).*"	goodbye+cruel+world\u0026param=val
"q=(?<q>[a-zA-Z0-9%-_&+/^\\\\]+)"	goodbye+cruel+world\u0026param=val

Events tab data is like: 

Event

apple: honeycrisp
ball: baseball
car: Ferrari
query: param1=val1&param2=val2&param3=val3&q=goodbye+cruel+world&param=val
status: 200

... etc ...

SO, how can I get the q value to return just the first parameter, ignoring anything that has a \ or & before it and terminating just at q?

And please, if you would be so kind, include an explanation of why what you suggest works? 

Thanks

[ITWhisperer]

Not entirely sure whether your _raw field includes an & or \u0026, anyway for backslashes you have to escape the escape

| rex "q=(?<q>[^\\\\]+)"

[isxtn]

Thank you. The raw data is an actual "&" not the unicode.  Even when I take out the "&" from the regex I still get the unicode reply. 

And when I changed the regex to 

rex field=_raw "q=(?<q>[a-zA-Z0-9%-_&+/^\\\\]+)"

I still get the \u0026param=val ... 

Is there another pattern I should use? 

[ITWhisperer]

| rex "q=(?<q>[^&]+)"