UNIX-style RegExp Replace running extremely slowly under windows. Help? EDIT: Negative lookahead ass

Posted by John Sullivan on Stack Overflow See other posts from Stack Overflow or by John Sullivan
Published on 2010-03-30T19:06:40Z Indexed on 2010/03/30 19:53 UTC
Read the original article Hit count: 290

Filed under:

regex

|

regex-negation

I'm trying to run a unix regEXP on every log file in a 1.12 GB directory, then replace the matched pattern with ''. Test run on a 4 meg file is took about 10 minutes, but worked. Obviously something is murdering performance by several orders of magnitude.

Find: ^(?!.*155[0-2][0-9]{4}\s.*).*$ -- NOTE: match any line NOT starting 155[0-2]NNNN where in is a number 0-9. Replace with: ''.

Is there some justifiable reason for my regExp to take this long to replace matching text, or is the program I am using (this is windows / a program called "grepWin") most likely poorly optimized?

Thanks.

UPDATE: I am noticing that searching for ^(155[0-2]).$ takes ~7 seconds in a 5.6 MB file with 77 matches. Adding the Negative Lookahead Assertion, ?=, so that the regExp becomes ^(?!155[0-2]).$ is causing it to take at least 5-10 minutes; granted, there will be thousands and thousands of matches.

Should the negative lookahead assertion be extremely detrimental to performance, and/or a large quantity of matches?

© Stack Overflow or respective owner

Related posts about regex

Find multiple regex in each line and skip result if one of the regex doesn't match

as seen on Stack Overflow - Search for 'Stack Overflow'
I have a list of variables: variables = ['VariableA', 'VariableB','VariableC'] which I'm going to search for, line by line ifile = open("temp.txt",'r') d = {} match = zeros(len(variables)) for line in ifile: emptyCells=0 for i in range(len(variables)): regex = r'('+variables[i]+r')[:|=|\(](-… >>> More
OWASP Regex Repository: Is this regex correct?

as seen on Stack Overflow - Search for 'Stack Overflow'
I was looking at the regular expression for validating various data types from the (OWASP Regex Repository). One of the regular expressions in there is called safetext and looks like: ^[a-zA-Z0-9\s.\-]+$ My first question is: Is this regular expression correct? complementary question If this… >>> More
Make a Perl-style regex interpreter behave like a basic or extended regex interpreter

as seen on Stack Overflow - Search for 'Stack Overflow'
I am writing a tool to help students learn regular expressions. I will probably be writing it in Java. The idea is this: the student types in a regular expression and the tool shows which parts of a text will get matched by the regex. Simple enough. But I want to support several different regex… >>> More
JS regex isn't matching, even thought it works with a regex tester

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm writing a piece of client-side javascript code that takes a function and finds the derivative of it, however, the regex that's supposed to match with the power rule fails to work in the context of the javascript program, even though it sucessfully matches when it's used with an independent regex… >>> More
c# RegEx with "|"

as seen on Stack Overflow - Search for 'Stack Overflow'
I need to be able to check for a pattern with | in them. For example an expression like d*|*t should return true for a string like "dtest|test". I'm no regex hero so I just tried a couple of things, like: Regex Pattern = new Regex("s*\|*d"); //unable to build because of single backslash Regex Pattern… >>> More

Related posts about regex-negation

Why is negation of a regex needed?

as seen on Stack Overflow - Search for 'Stack Overflow'
There are so many questions on regex-negation here on SO. I am not sure I understand why people feel the need to negate a regex. Why not use something like grep -v that shows only the results that do not match the regex? $ ls april august december february january july june march may… >>> More
Regex to match a whole string only if it lacks a given substring/suffix

as seen on Stack Overflow - Search for 'Stack Overflow'
I've searched for questions like this, but all the cases I found were solved in a problem-specific manner, like using !g in vi to negate the regex matches, or matching other things, without a regex negation. Thus, I'm interested in a “pure” solution to this: Having a set of strings I need to filter… >>> More
How to negate the whole regex?

as seen on Stack Overflow - Search for 'Stack Overflow'
I have a regex, for example ([m]{2}|(t){1}). It matches ma and t and doesn't match bla. I want to negate the regex, thus it must match bla and not ma and t, by adding something to this regex. I know I can write bla, the actual regex is however more complex. >>> More
how to negate whole regex ??

as seen on Stack Overflow - Search for 'Stack Overflow'
I have regex (for example) ([m]{2}|(t){1}) and it matches ma and t and doesnt match bla I want it to match bla and doesnt match ma and t by adding something to this regex, i know i can write bla, my real-life regex is more complex. >>> More
Negating a set of words via java regex!

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi folks, I would like to negate a set of words using java regex. Say, I want to negate cvs, svn, nvs, mvc. I wrote a regex which is ^[(svn|cvs|nvs|mvc)]. Some how that seems not to be working. Could you please help? Thanks. .\J >>> More