I seen this code on a website
function filterPath(string) {
return string
.replace(/^\//,'')
.replace(/(index|default).[a-zA-Z]{3,4}$/,'')
.replace(/\/$/,'');
}
The result of this gave some really long code in nos,digits, and slashes and couldn't figure it out. Is it like a security trick or something like that.
I just cant seem to understand what is this "replace" function trying to achieve ?? If anyone could explain what does it mean...
These are regular expressions (called regex for short).
The actual expression is inside /.../ with \ beeing an escape character.
So /^\// holds an ^/ regex.
As for your exact expressions:
1. ^/: the / character at the begging of line (^)
2. (index|default).[a-zA-Z]{3,4}$:
3. the /$: / character at the end of line ($)
Related
I have an expression in Jenkinsfile:
myvar = myvar.substring(0, myvar.length() - 2)
The goal is to cut the EoL characters from the string (which contains the execution result of the batch command).
Recently I've installed GroovyLint plugin for VSCode and it complained about this line:
Violation in class None. The String.substring(int, int) method can be replaced with the subscript operatorGroovyLint(UnnecessarySubstring-1)
I've googled what is that subscript operator and it looks like the replacement would be something like this:
myvar = myvar[0..myvar.length() - 2]
but unfortunately, it does not work: it gives no visible error, but also makes no changes to the myvar.
What do I miss? Maybe you can't use variables as part of the subscript operator?
Maybe there is a better way to cut those end-of-line characters? I guess I could use regexp, but to me, that sounds like overkill.
Thanks!
Thanks to ernset_k, found the answer!
The problem was that the subscript operator includes the upper bound. In my original scenario, last 2 characters where not printable and that's why I did not see the difference while debugging. I had to use "myvar.length()-3".
But as indicated by ernest_k, instead of calculating the length of the string you need to trim, we can also use other options of the operator. All these examples work as expected:
println myvar[0..myvar.length() - 3]
println myvar[0..<-2]
println myvar[0..-3]
I'm trying to match the prefix of the string Something. For example, If input So,SOM,SomeTH,some,S, it is all accepted because they are all prefixes of Something.
My code
Ss[oO]|Ss[omOMOmoM] {
printf("Accept Something": %s\n", yytext);
}
Input
Som
Output
Accept Something: So
Invalid Character
It's suppose to read Som because it is a prefix of Something. I don't get why my code doesn't work. Can anyone correct me on what I am doing wrong?
I don't know what you think the meaning of
Ss[oO]|Ss[omOMOmoM]
is, but what it matches is either:
an S followed by an s followed by exactly one of the letters o or O, or
an S followed by an s followed by exactly one of the letters o, O, m or M. Putting a symbol more than once inside a bracket expression has no effect.
Also, I don't see how that could produce the output you report. Perhaps there was a copy-and-paste error, or perhsps you have other pattern rules.
If you want to match prefixes, use nested optional matches:
s(o(m(e(t(h(i(ng?)?)?)?)?)?)?)?
If you want case-insensitive matcges, you could write out all the character classes, but that gets tiriesome; simpler is to use a case-insensitve flag:
(?i:s(o(m(e(t(h(i(ng?)?)?)?)?)?)?)?)
(?i: turns on the insensitive flag, until the matching close parenthesis.
In practice, this is probably not what you want. Normally, you will want to recognise a complete word as a token. You could then check to see if the word is a prefix in the rule action:
[[:alpha:]]+ { if (yyleng <= strlen("something") && 0 == strncasemp(yytext, "something", yyleng) {
/* do something */
}
}
There is lots of information in the Flex manual.
Right now your code (as shown) should only match "Sso" or "SsO" or "Ssm" or "SsM".
You have two alternatives that each start with Ss (without square brackets) so those will be matched literally. That's followed by either [oO] or [omOMomoM], but the characters in square brackets represent alternatives, so that's equivalent to [oOmM] --i.e., any one character of of o, O, m or M.
I'd start with: %option caseless to make it a case-insensitive scanner, so you don't have to list the upper- and lower-case equivalents of every letter.
Then it's probably easiest to just list the alternatives literally:
s|so|som|some|somet|someth|somethi|somethin|something { printf("found prefix"); }
I guess you can make the pattern a bit shorter (at least in the source code) by doing something on this order:
s(o(m(e(t(h(i(n(n(g)?)?)?)?)?)?)?)?)? { printf("found prefix"); }
Doesn't seem like a huge improvement to me, but some might find it more attractive than I do.
If you don't want to use %option caseless the basic idea helps more:
[sS]([oO]([mM]([eE]([tT]([hH]([iI]([nN]([gG])?)?)?)?)?)?)?)? { printf("found prefix"); }
Listing every possible combination of upper and lower case would get tedious.
Hi I've been struggling with this for the last hour and am no closer. How exactly do I strip everything except numbers, commas and decimal points from a rails string? The closest I have so far is:-
rate = rate.gsub!(/[^0-9]/i, '')
This strips everything but the numbers. When I try add commas to the expression, everything is getting stripped. I got the aboves from somewhere else and as far as I can gather:
^ = not
Everything to the left of the comma gets replaced by what's in the '' on the right
No idea what the /i does
I'm very new to gsub. Does anyone know of a good tutorial on building expressions?
Thanks
Try:
rate = rate.gsub(/[^0-9,\.]/, '')
Basically, you know the ^ means not when inside the character class brackets [] which you are using, and then you can just add the comma to the list. The decimal needs to be escaped with a backslash because in regular expressions they are a special character that means "match anything".
Also, be aware of whether you are using gsub or gsub!
gsub! has the bang, so it edits the instance of the string you're passing in, rather than returning another one.
So if using gsub! it would be:
rate.gsub!(/[^0-9,\.]/, '')
And rate would be altered.
If you do not want to alter the original variable, then you can use the version without the bang (and assign it to a different var):
cleaned_rate = rate.gsub!(/[^0-9,\.]/, '')
I'd just google for tutorials. I haven't used one. Regexes are a LOT of time and trial and error (and table-flipping).
This is a cool tool to use with a mini cheat-sheet on it for ruby that allows you to quickly edit and test your expression:
http://rubular.com/
You can just add the comma and period in the square-bracketed expression:
rate.gsub(/[^0-9,.]/, '')
You don't need the i for case-insensitivity for numbers and symbols.
There's lots of info on regular expressions, regex, etc. Maybe search for those instead of gsub.
You can use this:
rate = rate.gsub!(/[^0-9\.\,]/g,'')
Also check this out to learn more about regular expressions:
http://www.regexr.com/
I'm trying to look at a string and reject anything that has seq= or app= in the string. Where it gets tricky is I need elements with q=something or p=something.
The seq= part of the string is always preceded an & and app= is always preceded by a ?
I have absolutely no idea where to start. I've been using http://www.rubular.com/ to try and figure it out but to no avail.
Any help would be hugely appreciated.
Based on your question, I believe you could just reject any strings that match the following expression:
[\?&](?:seq|app)=
This will match any string that contains a ? or & followed by either app= or seq=. The ?: inside the parentheses just tells the regular expression not to bother to capture matching groups as sub-matches. They're not really necessary, but what the heck.
Here's a Rubular link with some samples.
Could anybody help me make a proper regular expression from a bunch of text in Ruby. I tried a lot but I don't know how to handle variable length titles.
The string will be of format <sometext>title:"<actual_title>"<sometext>. I want to extract actual_title from this string.
I tried /title:"."/ but it doesnt find any matches as it expects a closing quotation after one variable from opening quotation. I couldn't figure how to make it check for variable length of string. Any help is appreciated. Thanks.
. matches any single character. Putting + after a character will match one or more of those characters. So .+ will match one or more characters of any sort. Also, you should put a question mark after it so that it matches the first closing-quotation mark it comes across. So:
/title:"(.+?)"/
The parentheses are necessary if you want to extract the title text that it matched out of there.
/title:"([^"]*)"/
The parentheses create a capturing group. Inside is first a character class. The ^ means it's negated, so it matches any character that's not a ". The * means 0 or more. You can change it to one or more by using + instead of *.
I like /title:"(.+?)"/ because of it's use of lazy matching to stop the .+ consuming all text until the last " on the line is found.
It won't work if the string wraps lines or includes escaped quotes.
In programming languages where you want to be able to include the string deliminator inside a string you usually provide an 'escape' character or sequence.
If your escape character was \ then you could write something like this...
/title:"((?:\\"|[^"])+)"/
This is a railroad diagram. Railroad diagrams show you what order things are parsed... imagine you are a train starting at the left. You consume title:" then \" if you can.. if you can't then you consume not a ". The > means this path is preferred... so you try to loop... if you can't you have to consume a '"' to finish.
I made this with https://regexper.com/#%2Ftitle%3A%22((%3F%3A%5C%5C%22%7C%5B%5E%22%5D)%2B)%22%2F
but there is now a plugin for Atom text editor too that does this.