Regex 0 or 1 occurrences

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Regex 0 or 1 occurrences

This will examine many techniques to determine in C. Net: the Fastest Way to count substring occurrences in a string. This test stemmed from a project where I had to do a lot of substring searches. Contains or IndexOf straight out of the box because they only test to see if a substring exists, not how many times a string occurs in another string.

Also, if you followed my Fastest Way to check if a string occurs within a string benchmarks:. If so, what is the fastest way to count substring occurrences within another string? A C Console application was written to test several counting techniques: 5 single-threaded; 5 multi-threaded.

The code is written in Visual Studio targeting.

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Net Framework version 4. The source code is available at the end of this blog so you can benchmark it on your own system if you wish.

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Split ; count results. C Regex. However, if you have a great alternative solution, please post! The test was run for each technique over the following number of comparisons:. Yes in most cases, programmers are only going to test if 1 or 2 strings occur in another string. Before starting, my hypothesis was that I expected the variations of the custom counting method to be the winner since it generally does perform the best whether counting substring occurrences in strings or characters in strings.

All times are indicated in hours:minutes:seconds. Yes, some took over an hour! Lower numbers are better because they indicate faster performance. Counting the number of occurrences of 1 string in each of. Counting the number of occurrences of strings in each of.

Counting the number of occurrences of 1, strings in each of. The technique T1 implementing a common counting method won by running faster every single time.

In more than half the tests it completed roughly twice as fast as the next fastest technique, T2 from DotNetPerls.

regex 0 or 1 occurrences

The real surprise was how the single-threaded T1, in most cases, ran faster than half the multi-threaded parallel techniques even at the higher string counts!

The other techniques were respectable: not the greatest, not the worst. On my system, unless someone spots a flaw in my test code, Technique 1 with the common counting method was the single-threaded winner.

Basic Regular Expressions: Zero or One

Implementing the parallel version was the multi-threaded winner. Any application that needs micro optimization or where speed is of the essence, nothing else should be considered. Otherwise, there are two other techniques that can be utilized. It really comes down to personal taste and how much one cares about code readability versus speed. Length - ss[x]. Replace sf[y], String.

Length - ss [ x ]. Replace sf [ y ]String. Length. IndexOf sf[y], z! IndexOf sf [ y ]z! Count - 1. Matches ss[x], Regex.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. It only takes a minute to sign up. Its expansion would include aakakkand akkkbut not akc.

Except for ksh93none of the usual shells have regular expressions with the same syntax as sed, awk, etc. Ksh93, bash and zsh have regular expressions with a different syntax that's backward compatible with globs:. So in bash you'd write. See also Why does my regular expression work in X but not in Y? This isn't convenient for listing files though, but if you really want it, it can be done. If you want to use regexps to find matching filenames, you can use the find command:.

The -maxdepth 1 option limits the search to just the current directory no subdirectories will be searched. There are numerous methods for using the files found by find in other commands. For example:. The last example is prone to various failure modes, including 1. On Ubuntu Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Match-zero-or-more operator in shell globbing Ask Question.

Asked 4 years, 5 months ago. Active 4 years, 5 months ago. Viewed 6k times. Blacklight Shining 2 2 silver badges 11 11 bronze badges. Kira Kira 3, 1 1 gold badge 11 11 silver badges 26 26 bronze badges.Both patterns and strings to be searched can be Unicode strings str as well as 8-bit strings bytes.

However, Unicode strings and 8-bit strings cannot be mixed: that is, you cannot match a Unicode string with a byte pattern or vice-versa; similarly, when asking for a substitution, the replacement string must be of the same type as both the pattern and the search string. This behaviour will happen even if it is a valid escape sequence for a regular expression.

Usually patterns will be expressed in Python code using this raw string notation. It is important to note that most regular expression operations are available as module-level functions and methods on compiled regular expressions.

The third-party regex module, which has an API compatible with the standard library re module, but offers additional functionality and a more thorough Unicode support. A regular expression or RE specifies a set of strings that matches it; the functions in this module let you check if a particular string matches a given regular expression or if a given regular expression matches a particular string, which comes down to the same thing.

Regular expressions can be concatenated to form new regular expressions; if A and B are both regular expressions, then AB is also a regular expression. In general, if a string p matches A and another string q matches Bthe string pq will match AB.

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This holds unless A or B contain low precedence operations; boundary conditions between A and B ; or have numbered group references. Thus, complex expressions can easily be constructed from simpler primitive expressions like the ones described here. For details of the theory and implementation of regular expressions, consult the Friedl book [Frie09]or almost any textbook about compiler construction.

A brief explanation of the format of regular expressions follows. Regular expressions can contain both special and ordinary characters. Most ordinary characters, like 'A''a'or '0'are the simplest regular expressions; they simply match themselves. You can concatenate ordinary characters, so last matches the string 'last'.

Some characters, like ' ' or ' 'are special. Special characters either stand for classes of ordinary characters, or affect how the regular expressions around them are interpreted. This avoids ambiguity with the non-greedy modifier suffix? To apply a second repetition to an inner repetition, parentheses may be used. For example, the expression? In the default mode, this matches any character except a newline. More interestingly, searching for foo.

Causes the resulting RE to match 0 or more repetitions of the preceding RE, as many repetitions as are possible. Causes the resulting RE to match 1 or more repetitions of the preceding RE. Causes the resulting RE to match 0 or 1 repetitions of the preceding RE. Specifies that exactly m copies of the previous RE should be matched; fewer matches cause the entire RE not to match.

Causes the resulting RE to match from m to n repetitions of the preceding RE, attempting to match as many repetitions as possible.News II.

Java - Regular Expressions

Introduction 2. Substitute Command 3. Pattern Description 4. Global Command 5. Examples 6.

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Vim is an improved in many ways version of vi, a ubiquitous text editor found on any UNIX system. VIM was created by Bram Moolenaar with a help of other people.

regex 0 or 1 occurrences

It's free but if you like it you can make a charitable contribution to orphans in Uganda. Vim has its own web site, www.

Vim was successfully ported to nearly all existing OS. It is a default editor in many Linux distributions e. VIM has all features of a modern programmer's editor - macro language, syntax highlighting, customizable user interface, easy integration with various IDEs plus a set of features which makes VIM so attractive to its users: crash recovery, automatic commands, session management.

regex 0 or 1 occurrences

VIM has a very broad and loyal user base. Over 10 million people have it installed counting only Linux users. Estimation is that there are about half a million people using Vim as their main editor. And this number is growing. I started this tutorial for one simple reason - I like regular expressions.

Nothing compares to the satisfaction from a well-crafted regexp which does exactly what you wanted it to do I hope it's passable as a foreword. Speaking more seriously, regular expressions or regexps for short are tools used to manipulate text and data.

The best known example is UNIX grep, a program to search files for lines that match certain pattern. The search pattern is described in terms of regular expressions. You can think of regexps as a specialized pattern language. Regexps are quite useful and can greatly reduce time it takes to do some tedious text editing. Feel free to send me volontir at yahoo dot com your comments.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. Learn more. Asked 9 years, 4 months ago. Active 2 years ago. Viewed k times. Prem Prem 4, 10 10 gold badges 35 35 silver badges 61 61 bronze badges.

Just hover over symbol in their website where you've put your regex. Active Oldest Votes. Jeff Ferland Jeff Ferland So we can seek i. It is very confusing.

That's because in the shell globbing is used which is not a regular expression. They both allow matching of patterns but are completely different.

Count of occurrences of a “1(0+)1” pattern in a string

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Trying to find out a regex to match exactly 4 numbers with 0 or 1 occurrence of ". Learn more.

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Asked 2 years, 2 months ago. Active 1 year, 9 months ago. Viewed 1k times.

Regular Expressions (RegEx) Tutorial #4 - Ranges

DevOops DevOops 1 1 gold badge 3 3 silver badges 16 16 bronze badges. One way to do this is to expressly match the number of characters you need.

Just keep going like that. Not sure what you need. Active Oldest Votes.

regex 0 or 1 occurrences

Srdjan M. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Featured on Meta.Searches an input string for all occurrences of a regular expression and returns all the matches. Searches the specified input string for all occurrences of a regular expression, beginning at the specified starting position in the string. Searches the specified input string for all occurrences of a specified regular expression, using the specified matching options.

Searches the specified input string for all occurrences of a specified regular expression, using the specified matching options and time-out interval. A collection of the Match objects found by the search.

If no matches are found, the method returns an empty collection object. The following example uses the Matches String method to identify any words in a sentence that end in "es". The Matches String method is similar to the Match String method, except that it returns information about all the matches found in the input string, instead of a single match. It is equivalent to the following code:. The regular expression pattern for which the Matches String method searches is defined by the call to one of the Regex class constructors.

For more information about the elements that can form a regular expression pattern, see Regular Expression Language - Quick Reference. The Matches method uses lazy evaluation to populate the returned MatchCollection object. Accessing members of this collection such as MatchCollection. Count and MatchCollection. CopyTo causes the collection to be populated immediately.

To take advantage of lazy evaluation, you should iterate the collection by using a construct such as foreach in C and For Each … Next in Visual Basic. Because of its lazy evaluation, calling the Matches String method does not throw a RegexMatchTimeoutException exception. However, the exception is thrown when an operation is performed on the MatchCollection object returned by this method, if the MatchTimeout property is not Regex. InfiniteMatchTimeout and a matching operation exceeds the time-out interval.

The following example uses the Match String method to find the first word in a sentence that ends in "es", and then calls the Matches String, Int32 method to identify any additional words that end in "es".

The Matches String, Int32 method is similar to the Match String, Int32 method, except that it returns information about all the matches found in the input string, instead of a single match. The regular expression pattern for which the Matches String, Int32 method searches is defined by the call to one of the Regex class constructors.

The following example uses the Matches String, String method to identify any word in a sentence that ends in "es".


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