I am looking for a regex that will give me the index of the last space in a string using javascript.
I was using goolge to find a suitable regex, but no success.
Even the SO-Question Regex to match last space character does not hold a solution because the goal there was to remove more than one character in the end.
What is the correct regex?
As I commented I would just use lastIndexOf() but here is a regex solution:
The regex / [^ ]*$/ finds the last space character in a string. Use it like this:
// Alerts 9
alert("this is a str".search(/ [^ ]*$/));
The correct solution is not using a regex at all but the built-in lastIndexOf method strings have. Regexes are meant to match strings, not give you indexes (even though grouped matchs may be returned as index+length instead of a string - C-based regex libraries usually do so to avoid unnecessary copying)
Related
I need to write a little RegEx matcher which will match any occurrence of strings in the form of
[a-zA-Z]+(_[a-zA-Z0-9]+)?
If I use the regex above it does match the sections needed but would also match onto the abc part of 4_abc which is not intended. I tried to exclude it with:
(?:[^a-zA-Z0-9_]|^)([a-zA-Z]+(_[a-zA-Z0-9]+)?)(?:[^a-zA-Z0-9_]|$)
The problem is that the 'not' matches at the beginning and end are not really working like I hoped they would. If I use them on the example
a_d Dd_da 4_d d_4
they would block matching the second Dd_da because the space was used in the first match.Sadly I can't use lookarounds because I am using JS.
So the input:
a_d Dd_da 4_d d_4
should match: a_d, Dd_da and d_4
but matches: a_d (there is a space at the end)
Is there another way to match the needed sections, or to not consume the 'anchor' matches?
I really appreciate your help.
You can make use of \b:
\b[a-zA-Z]+(_[a-zA-Z0-9]+)?\b
\b matches the (zero-width) point where either the preceding character or following character is a letter, digit or underscore, but not both. It also matches with the start/end of the string if the first/last character is a letter, digit or underscore.
I am using javascript .replace() to remove a word from a comma separated list of words and have a solution that works, but it is clumsy and I think there must be a better one.
regex looks like:
/,word1|word1,?/
The handles the cases of leading, embedded and trailing and removes the correct number of commas eg.
word1,word2,word3
word2,word1,word3
word2,word3,word1
All result in word2,word3
word1 on its own is removed completely
Is there a way to do it without that repeated word1 in the regex pattern?
There are no really better or shorter patterns to do that. All you can do is to avoid false positive by adding word boundaries where the comma may be missing:
,word1\b|\bword1\b,?
If you have to deal with a large string, and only if the first letter isn't too frequent, you can try to use the first character discrimination technic to reduce the number of positions where the pattern will be tested:
(?=[,w])(?:,word1\b|\bword1\b,?)
(note that you need to test that in real life to see if it is really benefic.)
Other way without regex
if your target string is only a comma separated list, using a split/join stay the best solution.
Tried to search for /\,$/ online, but coudnt find anything.
I have:
coords = coords.replace(/\,$/, "");
Im guessing it returns coords string index number. What I have to search online for this, so I can learn more?
/\,$/ finds the comma character (,) at the end of a string (denoted by the $) and replaces it with empty (""). You sometimes see this in regex code aiming to clean up excerpts of text.
It's a regular expression to remove a trailing comma.
That thing is a Regular Expression, also known as regex or regexp. It is a way to "match" strings using some rules. If you want to learn how to use it in JavaScript, read the Mozilla Developer Network page about RegExp.
By the way, regular expressions are also available on most languages and in some tools. It is a very useful thing to learn.
That's a regular expression that finds a comma at the end of a string. That code removes the comma.
// defines a JavaScript regular expression, used to match a pattern within a string.
\,$ is the pattern
In this case \, translates to ,. A backslash is used to escape special characters, but in this case, it's not necessary. An example where it would be necessary would be to remove trailing periods. If you tried to do that with /.$/ the period here has a different meaning; it is used as a wildcard to match [almost] any character (aside for some newlines). So in this case to match on "." (period character) you would have to escape the wildcard (/\.$/).
When $ is placed at the end of the pattern, it means only look at the end of the string. This means that you can't mistakingly find a comma anywhere in the middle of the string (e.g., not after help in help, me,), only at the end (trailing). It also speeds of the regular expression search considerably. If you wanted to match on characters only at the beginning of the string, you would start off the pattern with a carat (^), for instance /^,/ would find a comma at the start of a string if one existed.
It's also important to note that you're only removing one comma, whereas if you use the plus (+) after the comma, you'd be replacing one or more: /,+$/.
Without the +; trailing commas,, becomes trailing commas,
With the +; no trailing comma,, becomes no trailing comma
I'm writing a javascript function which takes a regex and some elements against which it matches the regex against the name attribute.
Let's say i'm passed this regex
/cmw_step_attributes\]\[\d*\]/
and a string that is structured like this
"foo[bar][]chicken[123][cmw_step_attributes][456][name]"
where all the numbers could vary, or be missing. I want to match the regex against the string in order to swap out the 456 for another number (which will vary), eg 789. So, i want to end up with
"foo[bar][]chicken[123][cmw_step_attributes][789][name]"
The regex will match the string, but i can't swap out the whole regex for 789 as that will wipe out the "[cmw_step_attributes][" bit. There must be a clean and simple way to do this but i can't get my head round it. Any ideas?
thanks, max
Capture the first part and put it back into the string.
.replace(/(cmw_step_attributes\]\[)\d*/, '$1789');
// note I removed the closing ] from the end - quantifiers are greedy so all numbers are selected
// alternatively:
.replace(/cmw_step_attributes\]\[\d*\]/, 'cmw_step_attributes][789]')
Either literally rewrite part that must remain the same in replacement string, or place it inside capturing brackets and reference it in replace.
See answer on: Regular Expression to match outer brackets.
Regular expressions are the wrong tool for the job because you are dealing with nested structures, i.e. recursion.
Have you tried:
var str = 'foo[bar][]chicken[123][cmw_step_attributes][456][name]';
str.replace(/cmw_step_attributes\]\[\d*?\]/gi, 'cmw_step_attributes][XXX]');
I need to match all occurrences of // in a string in a Javascript regex
It can't match /// or /
So far I have (.*[^\/])\/{2}([^\/].*)
which is basically "something that isn't /, followed by // followed by something that isn't /"
The approach seems to work apart from when the string I want to match starts with //
This doesn't work:
//example
This does
stuff // example
How do I solve this problem?
Edit: A bit more context - I am trying to replace // with !, so I am then using:
result = result.replace(myRegex, "$1 ! $2");
Replace two slashes that either begin the string or do not follow a slash,
and are followed by anything not a slash or the end of the string.
s=s.replace(/(^|[^/])\/{2}([^/]|$)/g,'$1!$2');
It looks like it wouldn't work for example// either.
The problem is because you're matching // preceded and followed by at least one non-slash character. This can be solved by anchoring the regex, and then you can make the preceding/following text optional:
^(.*[^\/])?\/{2}([^\/].*)?$
Use negative lookahead/lookbehind assertions:
(.*)(?<!/)//(?!/)(.*)
Use this:
/([^/]*)(\/{2})([^/]*)/g
e.g.
alert("///exam//ple".replace(/([^/]*)(\/{2})([^/]*)/g, "$1$3"));
EDIT: Updated the expression as per the comment.
/[/]{2}/
e.g:
alert("//example".replace(/[/]{2}/, ""));
This does not answer the OP's question about using regex, but since some of the original comments suggested using .replaceAll, since not everyone who reads the question in the future wants to use regex, since people might mistakenly assume that regex is the only alternative, and since these details cannot be accommodated by submitting a comment, here's a poor man's non-regex approach:
Temporarily replace the three contiguous characters with something that would never naturally occur — really important when dealing with user-entered values.
Replace the remaining two contiguous characters using .replaceAll().
Return the original three contiguous characters.
For instance, let's say you wanted to remove all instances of ".." without affecting occurrences of "...".
var cleansedText = $(this).text().toString()
.replaceAll("...", "☰☸☧")
.replaceAll("..", "")
.replaceAll("☰☸☧", "...")
;
$(this).text(cleansedText);
Perhaps not as fast as regex for longer strings, but works great for short ones.