I am testing in Powershell, some regex that I get from a program written in another language.
But the regex arent working properly, I know that depending on the regex flavor like PCRE,POSIX. The regex is interpreted in different way.
My question is what are the compatible regex Flavors for powershell?
The correct flavor is .Net regex, but in online testers like debuggex that don't have it, I use PCRE and it seems to work fairly well.
Other issues you may run into are whether or not you need to escape certain characters in the string for powershell (irrespective of characters that need to be escaped for the regex engine).
Related
I want to learn more about the regex syntax of the search and replace function in eclipse c++.
Does it use it's own regex syntax(in this case anyone knows a good tutorial) or does it use the syntax of another language(like java regex, grep, perl regex)?
Eclipse search and replace feature uses Java regex:
The regular expression must respect Java Regex.
However, one of the peculiarities is that you cannot match zero-legnth strings (i.e. (?=,) won't match the empty string before ,). In such cases, use capturing groups in the regex and use backreferences to those groups in the replacement patterns (e.g. to add newlines after a comma use , in the search and $0\n in the replacement).
I'm currently writing a little flatfile database for a project and in that context need to escape list item delimiters.
I decided to use ; as the delimiter and /; as my escaped version of that.
Since I already used RegEx lookarounds in the past, I was sure the following expression I use to split would do the job.
(?<!/);
My expression should match the ; in
abc;def
but should not match the ; in
abc/;def
I used RegExPal and the expression doesn't fit any of my examples.
Isn't this the correct structure of a regular expression to achieve my goal?
(?<!ForbiddenPreceedingExpression)CharacterFollowing
Any hints on where to find my problem?
There is nothing wrong with the regex.
The problem is that Regexpal is a javascript regular expression tester. Java script does not support look behinds.
Take a look at
pcre(php) Demo
where as this one won't
Javascript Demo
Tried searching for regex found in this answer:
(,)(?=(?:[^']|'[^']*')*$)
I tried doing a search in Sublime and it worked out (around 700 results). When trying to replace the results it runs out of memory. Tried /(,)(?=(?:[^']|'[^']*')*$) in vim for searching first but it does not find any instances of the pattern. Also tried escaping all the ( and ) with \ in the regex.
Vim uses its own regular expression engine and syntax (which predates PCRE, by the way) so porting a regex from perl or some other editor will most likely need some work.
The many differences are too numerous to list in detail here but :help pattern and :help perl-patterns will help.
Anyway, this quick and dirty rewrite of your regular expression seems to work on the sample given in the linked question:
/\v(,)(\#=([^']|'[^']*')*$)
See :help \#= and :help \v.
One possible explanation is that the regular expression engine used in Sublime is different than the engine used in vim.
Not all regex engines are created equal; they don't all support the same features. (For example, a "negative lookahead" feature can be very powerful, but not all engines support it. And the syntax for some features differs betwen engines.)
A brief comparison of regular expression engines is available here:
http://en.wikipedia.org/wiki/Comparison_of_regular_expression_engines
Unfortunately Vim uses a different engine, and "normal" regular expressions won't work.
The regex you've mentioned isn't perfect: it doesn't skip escaped quotes, but, as I understand, it's good enough for you. Try this one, and if it doesn't match something, please send me that piece.
\v^([^']|'[^']*')*\zs,
A little explanation:
\v enables very magic search to avoid complex escaping rules
([^']|'[^']*') matches all symbols but quote and a pair of qoutes
\zs indicates the beginning of selection; you can think of it as of a replacement for lookbehind.
You have to escape the |, otherwise it doesn't work under vim. You should also escape the round brackets, unless you are searching for the '(' or ')' characters.
More information on regex usage in vim can be found on vimregex.com.
Assuming I have to check if "#" exists on a given string - should I use back slash before or not? So far I found they're both working for me, but I'm not sure if it always works on any Windows host (this is part of a VB.NET application that has to work world-wide)
The string: Hello #world
Pattern1: Hello #world
Pattern 2: Hello \#world
Which one should I use to get the most precise matching? pattern1 or pattern2?
I work with VB.NET on VS2010 (.NET FW 3.5)
Thank you
# is not a special regex character, at least not in VB.NET. Which means that both patterns are pretty much the same, and you can use whichever you prefer. Although for readability sake you probably should stick to the pattern without backslash.
You can find complete list of special regex characters in .NET here.
I would suggest you to leave this option on Regex engine. Just use its Regex.Escape function. It will escape the necessary things.
I have got a weird thing to solve in perl using regular expressions.
Consider the strings -
abcdef000000123
blaDeF002500456
wefdEF120045423
All of these strings are matching with the below regular expression when I tried in C with pcre library support :
???[dD][eE][fF][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]
But I'm unable to achieve the same in perl code. I'm getting some weird errors.
Please help with the piece of perl code with which these two things match.
Thanks in advance...
? is called quantifier that makes preceding pattern or group an optional match. Independently ? doesn't make any sense in regex and you are getting an error like: Quantifier follows nothing in regex.
Following regex should work for you in perl:
...[dD][eE][fF][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]
OR even more concise regex:
.{3}[dD][eE][fF][0-9]{9}
Each dot means match any character.
PS: You probably are getting confused by shell's glob vs regex.
That looks more like a file system regex than a PCRE. In Perl, the ? is a quantifier, not a wild card. You may want to replace them with . to get the same results in anything Perl compatible.
I might use ...[dD][eE][fF][0-9]{9} or even replace the [0-9] with \d.
qr/[A-z]{3}def[0-9]{9}/i
should be the Perl Regex object used to validate the mentioned strings.
Regards