Regex question mark. sed -n '/pattern/p' test.
Regex question mark Jul 23, 2015 · Given that the string can contain spaces (as per the edit), the correct regex is ^[ ?]*[?][ ?]*$ This allows for any number of spaces and question marks and guarantees that at least one question mark is present. Jan 3, 2019 · Consider though that it may be faster not to use regex and just do a simple "string contains" check for the presence of a question mark if that's literally all you're doing, and don't require complex pattern matching and value capture Jun 10, 2017 · Question mark in regex not working as expected. Viewed 619 times 1 It is probably quite simple, but I Jun 30, 2020 · The Question Mark (?) In regex, the meta character “?” makes the preceding character optional. I am really confused by studying this regex. In regular expression a question mark stands for a single symbol. In most regex implementations, a question mark means that the previous item is optional, while an escaped question mark (\?) is a literal question mark. Could we sch Oct 20, 2012 · ? is not a metacharacter in basic grep, so if you're grepping for a?, you are in fact grepping for a followed by a question mark. One such quantifier is the question mark?. Feb 28, 2022 · (question mark) Makes the preceding item optional. Defining the Question Mark (?) Nov 5, 2011 · In most regex implementations, a question mark means that the previous item is optional, while an escaped question mark (\?) is a literal question mark. So for example: To write an expression representing all 4 letter words starting with a you have to use the expression a???. Sep 13, 2016 · (. I'm not good with regex, i just know a bit of what can be done. See the regular expression, test string examples, and detailed explanation of the regex syntax and flags. 2. ) Apr 30, 2020 · So it sounds like one way to try to learn this stuff is to follow along with the online resources like regex. Modified 7 years, As to the regular expression, Nov 5, 2011 · Others work the other way around, and only take on special meaning when escaped (e. You have a question mark followed by a space, so there is no word boundary there and the regex will not find one. represents any single character (usually excluding the newline character), while * is a quantifier meaning zero or more of the preceding regex atom (character or group). This quantifier cannot appear after an Sep 3, 2015 · In order to pass variables into JS regex when using constructor notation, you need to escape all characters that act as regex special characters (quantifiers, group delimiters, etc. Aug 18, 2015 · The question mark matches exactly one character. Also: You're using a basic regular expression (no -r or -E option), so ? is not a special char. *? followed by digit \d abc. I think your regex needs some rethinking. This tells the regex engine to interpret the question mark as a literal character rather than a special regex operator. – Feb 4, 2022 · The regex Great\? matches the literal string Great followed by a literal question mark. See examples, syntax, and how to control greediness and alternatives with curly braces. Sep 9, 2016 · You may be confusing regular expressions with shell globs. An eg : Oct 9, 2020 · Google engineers are regular expression masters. The ? character serves as a single-character "wild card" for filename expansion in globbing… Performance. Jun 8, 2016 · A question mark represents any single letter (or symbol). See examples of how to make RegEx less greedy and more accurate with the zero or one quantifier. regular expression by question mark (Java) 2. I can't make the question mark quantifier work. dot metacharacter. And these, again, can vary between regex implementations. As an alternative, you can use the -r or --regexp-extended option to use the "extended regular expression syntax", which reverses the meaning of escaped and Sep 8, 2014 · Regular expression engines are built to match text (from left to right). The escape function is available at MDN Web site : Jul 7, 2014 · The safest way to store a list of options and arguments in variables is to use an array:. Dec 30, 2010 · The right way to escape any text for Regular Expression in java is to use: String quotedText = Pattern. (Technically you shouldn't put a backslash before ] but I don't know of an implementation that treats ] and \] differently outside of bracket expressions. I would like to get all my sentences back that have a question mark. find did not output anything because there were no directory names that matched the -name specification. Apr 3, 2022 · The command will only output lines that contain precisely one exclamation mark. Your regex matches abc followed by zero or more anything's un-greedily . In this case the name is specified as any directory with the second character of the directory name 'd', followed by any other characters. Any character means letters uppercase or lowercase, digits 0 through 9, and symbols such as the dollar ($) sign or the pound (#) symbol, punctuation mark (!) such as the question mark (?) commas (,) or colons (:) as well as Apr 7, 2017 · Regexp that ignores everything after a question mark symbol. In regex, the dot corresponds to any character except a newline character. Aug 9, 2023 · Learn how to use regex to match and validate question mark symbols '?' in text. You can specify a range of characters by using a hyphen, but if the hyphen appears as the first or last character enclosed in the square brackets, it is taken as a literal hyphen to be included in the character class as a normal character. Facebook engineers are regular expression masters. sed -n '/pattern/p' test. Apr 5, 2018 · Usage of question mark in regular expression. The regular expression (?!\S) is a negative lookahead assertion which succeeds either at the end of the string, or else when the next character is a whitespace character. Could someone give me a regex that would work? (java) If it's possible then i would like to return the bold in the next example: Dec 12, 2019 · CHECK Regular expression; Replace all; Explanation: \? # question mark, have to be escaped \h+ # 1 or more horizontal spaces \K # forget all we have seen until this Jan 8, 2014 · Hey Experts i am new to regex. awk 'gsub("!","&") == 1' file You can do something similar with Perl and its tr operator: perl -ne 'print if tr /!/!/ == 1' file With grep you can do it as follows, which avoids trying to be smart: Feb 17, 2017 · I guess it's a matter of opinion, but for me a regex that cannot include ? for zero or one matches is broken, and it's very common to run into sed commands that require this or \1. ) any number of times (*), as few times as possible to make the regex match (?). and needs no escaping. *?\\s to m Dec 6, 2024 · Not escaping question marks in regex expressions can lead to unexpected and incorrect results. For example, the In regexes, the question mark is an operator meaning one or none. Unlike some other quantifiers which focus on repetition, the question mark quantifier is all about optionality. Jul 2, 2013 · When a string is interpolated as a regex, it isn't matched literally, but interpreted as a regex. Therefore it is logical that when you ask an expression to match a range of character(s), it matches as many as possible. Java regex exact match with question mark and word boundary. Oct 7, 2012 · Python regex with question mark literal. Amazon engineers are regular expression masters. Your example could make sense either way around, but I suspect you have one of the dialects where ? is a literal and \? is the optional symbol. The thing is the use of question mark and equal to symbol in regex. Mar 8, 2012 · However, if a quantifier is followed by a question mark, then it becomes lazy, and instead matches the minimum number of times possible, so the pattern /\*. abc? matches abc or ab: no: YES: no: YES: Greedy quantifier? Makes the preceding item optional. Sep 13, 2016 · I used the regex tester at regex101. quote("any text goes here !?@ #593 ++ { ["); Then you can use the quotedText as part of the regular expression. Feb 20, 2010 · To make a regex non greedy (lazy) put a question mark after your greedy search e. ). *?\d you want to match abc followed by zero or more (maybe) lower case letters [a-z]* followed by digit \d Dec 28, 2020 · Colon : is simply colon. The {3} part is not relevant to the question, I used it to find 3 consecutive question marks. Modified 12 years, 1 month ago. php yields the same results. That's clear. If the question mark is not properly escaped, it may be interpreted as a literal question mark by the regex engine, leading to Regular expressions are teeming with quantifiers, each holding its own unique functionality. In this lesson, we'll shed light on this intriguing aspect of regex. If you were using egrep (aka grep -E), then answers indicating that ? is a zero-or-one-of-previous-entity regex metacharacter would be correct. Feb 2, 2016 · This is a simple question I think. Use '\'' to end up with a single quote in the regex. Apr 7, 2011 · Negative lookaheads are used if you want to match something not followed by something else. POSIX compliant regexes are described as 'obsolete regexes' in re_match man page and I agree with that term. Ask Question Asked 12 years, 3 months ago. Consider a word There; Now, by default, the RegEx e will find the third letter e in word Nov 6, 2024 · Learn how to use the question mark (?) to make the preceding token optional in regular expressions. Modified 12 years, 3 months ago. *?\*/ does the right thing with the C comments. In this expression question marks represent second, third and fourth letter. plain n is just a letter, but \n is a line feed). This feature is much more useful when you have a more complicated regex. 0. (. The reason your regex is not working is the \b at the end. com (no affiliation) to test these. But in a few dialects, it's the other way around. In regex, the question mark is a special character that indicates that the preceding character or group is optional. x(?!x2) example. I have found something which is very difficult to understand for me. Viewed 20k times 13 I'm using Oct 21, 2009 · I have the following in a text file: This is some text for cv_1 for example This is some text for cv_001 for example This is some text for cv_15 for example I am trying to use regex cv_. Mar 9, 2023 · Learn how to use the question mark ? metacharacter to specify 0 or 1 occurrences of a pattern in regular expressions. The Google search engine is a massive text-processing engine that extracts value from trillions of webpages. I write scripts that work on common Linux systems Write the regex between single quotes. The negative lookahead construct is the pair of parentheses, with the opening parenthesis followed by a question mark and an exclamation point. Put a backslash before $. *?) matches any character (. The question mark (?) in a regular expression has several meanings and may define: a quantifier a lazy match a group name property a look-around (assertion) And to determine what is its meaning, it just depends on the context where it's used. The call to regex_match will always return 0. Dec 6, 2024 · To properly escape a question mark in a regular expression , you can use a backslash before the question mark. Inside the regular expression, a dot operators represents any character except the newline character, which is \n. Therefore, we have to escape it: s/question\?/reply?/g Note that it isn't special in strings. Regular expressions with question mark. The dot: . In regular expression syntax . Social networks like Facebook, WhatsApp, and Instagram connect humans via text messages. I am trying to search for the occurrence of a string in another string using regex in JavaScript like so: var content ="Hi, I like your Apartment. Aug 29, 2012 · regex question mark in javascript. ) Nov 5, 2011 · Others work the other way around, and only take on special meaning when escaped (e. Ask Question Asked 7 years, 9 months ago. grep '<\?' test. So it creeps along gingerly. From the references above: The * character serves as a "wild card" for filename expansion in globbing. Apr 13, 2013 · I'm having troubles with std regex. php returns all lines - why? I expected it to output only the first line. */[\]^ and only those characters (but not inside bracket expressions). The question mark after the opening parenthesis is unrelated to the question mark at the end of the regex. g *? ?? +? What happens now is token 2 (+?) finds a match, regex moves along a character and then tries the next token (\b) rather than token 2 (+?). The meaning of the various quantifiers is not otherwise changed, just the preferred number of matches. Dec 4, 2015 · That is, I enclosed the question mark in character class brackets ( [and ]), which made the special meaning inactive. I also tried with {0,1} which doesn't behave like I expected eith Jun 15, 2021 · Python regex metacharacters Regex . The final question mark is the quantifier that makes the previous token optional. You'll get a match on any string, but you'll only capture a blank string because of the question mark. This symbol matches zero or one instance of the preceding character/group. Mar 14, 2012 · I got a big file with all my email activity over the last 5 years. By default, sed uses the " POSIX basic regular expressions syntax", so the question mark must be escaped as \? to apply its special meaning, otherwise it matches a literal question mark. It means nothing, except special cases like, for example, clustering without capturing (also known as a non-capturing group): (?:pattern) Nov 6, 2024 · The question mark and the colon after the opening parenthesis are the syntax that creates a non-capturing group. To express all words with at least one letter you can use expression Mar 28, 2013 · The question mark is identified by the shell as a single character. This is useful to build complex regexes, e. abc? matches abc or ab: YES: no: no: no: Greedy quantifier * (star) Sep 17, 2019 · yields the two lines containing the question mark. Nov 17, 2011 · The regular expression (?:^|\s) is a non-capturing group that matches either the start of the line or a whitespace character. g. But maybe, the < should be escaped, which yields another unexpected output. The & replaces the matched exclamation mark(s) with itself. com and learn the regular expression syntax there, but put everything inside single quotes when I'm trying it out with grep on the command line (unless I need to actually grep a single quote, then I'll have to jump through the hoops described above. Hot Network Questions Integral not italic dx when and Sep 15, 2021 · A single backslash is the correct way to escape a question mark \?. Jun 30, 2020 · The Question Mark (?) In regex, the meta character “?” makes the preceding character optional. Greedy, so the optional item is included in the match if possible. Oct 28, 2024 · Characters Meaning [xyz] [a-c] Character class: Matches any one of the enclosed characters. tl;dr: there is no detectable difference in performance. Ask Question Asked 12 years, 1 month ago. alr gwwvs ikqhl gdfzfo ivsql vvpnh ihiba vfruf flefpzh snsfdg