regex - Tcl greedy subexpression difference between + and * -

-

i trying understand tcl subexpression matches , "greediness" , stumped what's going on. referencing example found @ http://wiki.tcl.tk/396:

%regexp -inline (.*?)(n+)(.*) ennui en e n {}  %regexp -inline ^(.*?)(n+)(.*)$ ennui ennui e nn ui

notwithstanding fact don't understand "nested expressions" (that parenthesis indicate, right?) matching, decided start small , try difference between * , + greedy operators:

% regexp -inline (.*)(u*)(.*) ennui ennui ennui {} {} % regexp -inline (.*)(u+)(.*) ennui ennui enn u

if * matches 0 or more, , + matches 1 or more, don't understand difference in output between 2 commands. why u* , u+ produce 2 different results on same string?

i feel extremely important nuance - if can grasp what's going on in simple pattern match/regex, life made whole. help!

thanks in advance.

the reason (.*)(u*)(.*) , (.*)(u+)(.*) difference second regex requires @ least 1 u.

the regex in tcl uses backtracking (as nfas). (.*), engine grabs whole string beginning end, , starts backtracking find if can accommodate next subpattern.

in first expression, u optional (can 0 due *), thus, greedy .* decides won't yield characters. then, last .* can match 0 characters, again, no need give characters group.

in second expression, u obligatory, must occur @ least once. thus, engine grabs string first .*, backtracks, , founds u. so, puts starting sequence group 1, , matches , captures u (u+). since u 1, last (.*) matches , captures rest of string.


Comments

Post a Comment

Popular posts from this blog

c# - Store DBContext Log in other EF table -

-
i want store logs in db table (imported ef code). my code looks this: public pmcontext() : base("myentities") { configuration.proxycreationenabled = false; configuration.lazyloadingenabled = false; this.database.log = s => logstore(s); } private void logstore(string message) { tlog log = new tlog(); log.description = message; log.insertdate = datetime.now; logs.add(log); savechanges(); } public virtual dbset<tlog> logs { get; set; } i cannot use savechanges() (get error "sqlconnection not support parallel transactions") , if remove line nothing stored in db table. how can fix this? i think happens during savechanges call anywhere in app, because sql generated call logged, triggers nested savechanges call tries start own transaction. and there thing: savechanges call in logstore method trigger logging itself, you'd end starting infin...
Read more

Nuget pack csproj using nuspec -

-
i want create nuget package contains specified in nuspec file, still version csproj. in order use token have pack like: nuget pack myproj.csproj but when adds dependencies , creates unwanted folder in nuget package. nuspec file is: <?xml version="1.0" encoding="utf-8"?> <package xmlns="http://schemas.microsoft.com/packaging/2011/08/nuspec.xsd"> <metadata> <id>test</id> <version>$version$</version> <title>test</title> <authors>test</authors> <owners>test</owners> <requirelicenseacceptance>false</requirelicenseacceptance> <description>test</description> <summary>test</summary> <releasenotes>test</releasenotes> <copyright>test</copyright> </metadata> <files> <file src="bin\debug\*.dll" target="lib\net45" /> <file s...
Read more

javascript - Karma not able to start PhantomJS on Windows - Error: spawn UNKNOWN -

-
i lost "unknown" error: karma.conf.js: frameworks: ['mocha', 'should'], plugins: ['karma-mocha', 'karma-should', 'karma-phantomjs-launcher'], ... browsers: ['phantomjs'], error: 23 07 2015 14:35:37.691:warn [karma]: no captured browser, open http://localhost:9876/ 23 07 2015 14:35:37.701:info [karma]: karma v0.13.3 server started @ http://localhost:9876/ 23 07 2015 14:35:37.707:info [launcher]: starting browser phantomjs 23 07 2015 14:35:37.738:error [karma]: { [error: spawn unknown] code: 'unknown', errno: 'unknown', syscall: 'spawn' } error: spawn unknown @ exports._errnoexception (util.js:749:11) @ childprocess.spawn (child_process.js:1093:11) @ exports.spawn (child_process.js:933:9) @ object._execcommand (c:\users\jinga4x\git\mdl-sample-project\node_modules\karma\lib\launchers\process.js:63:21) @ object._start (c:\users\jinga4x\git\md...
Read more