Regular expression to match a line that doesn t contain a word

Question

I know it s possible to match a word and then reverse the matches using other tools  e g  grep -v   However  is it possible to match lines that do not contain a specific word  e g  hede  using a regular expression    Input   hoho hihi haha hede   Code   grep   lt Regex for  doesn t contain hede  gt   input   Desired output   hoho hihi haha

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The notion that regex doesn t support inverse matching is not entirely true  You can mimic this behavior by using negative look-arounds        hede        The regex above will match any string  or line without a line break  not containing the  sub string  hede   As mentioned  this is not something regex is  good  at  or should do   but still  it is possible    And if you need to match line break chars as well  use the DOT-ALL modifier  the trailing s in the following pattern          hede      s   or use it inline      s      hede          where the       are the regex delimiters  i e   not part of the pattern   If the DOT-ALL modifier is not available  you can mimic the same behavior with the character class   s S          hede   s S        Explanation  A string is just a list of n characters  Before  and after each character  there s an empty string  So a list of n characters will have n 1 empty strings  Consider the string  ABhedeCD         ----------------------------------------------------------  S     e1   A   e2   B   e3   h   e4   e   e5   d   e6   e   e7   C   e8   D   e9        ----------------------------------------------------------   index    0      1      2      3      4      5      6      7   where the e s are the empty strings  The regex    hede   looks ahead to see if there s no substring  hede  to be seen  and if that is the case  so something else is seen   then the    dot  will match any character except a line break  Look-arounds are also called zero-width-assertions because they don t consume any characters  They only assert validate something    So  in my example  every empty string is first validated to see if there s no  hede  up ahead  before a character is consumed by the    dot   The regex    hede   will do that only once  so it is wrapped in a group  and repeated zero or more times      hede      Finally  the start- and end-of-input are anchored to make sure the entire input is consumed       hede       As you can see  the input  ABhedeCD  will fail because on e3  the regex    hede  fails  there is  hede  up ahead

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A simpler solution is to use the not operator    Your if statement will need to match  contains  and not match  excludes      var contains    abc   var excludes   hede    if string match contains   amp  amp    string match excludes        proceed      I believe the designers of RegEx anticipated the use of not operators

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Since the introduction of ruby-2 4 1  we can use the new Absent Operator in Ruby   s Regular Expressions  from the official doc     abc  matches       ab    aab    cccc   etc  It doesn t match   abc    aabc    ccccabc   etc    Thus  in your case     hede   does the job for you  2 4 1  016  gt    hoho    hihi    haha    hede   select  s       hede    match s      gt    hoho    hihi    haha

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Maybe you ll find this on Google while trying to write a regex that is able to match segments of a line  as opposed to entire lines  which do not contain a substring  Tooke me a while to figure out  so I ll share   Given a string     lt span class  good  gt bar lt  span gt  lt span class  bad  gt foo lt  span gt  lt span class  ugly  gt baz lt  span gt    I want to match  lt span gt  tags which do not contain the substring  bad      lt span      bad      gt  will match  lt span class   good   gt  and  lt span class   ugly   gt    Notice that there are two sets  layers  of parentheses    The innermost one is for the negative lookahead  it is not a capture group  The outermost was interpreted by Ruby as capture group but we don t want it to be a capture group  so I added    at it s beginning and it is no longer interpreted as a capture group    Demo in Ruby   s     lt span class  good  gt bar lt  span gt  lt span class  bad  gt foo lt  span gt  lt span class  ugly  gt baz lt  span gt   s scan   lt span      bad      gt        gt     lt span class   good   gt      lt span class   ugly   gt

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If you re just using it for grep  you can use grep -v hede to get all lines which do not contain hede   ETA Oh  rereading the question  grep -v is probably what you meant by  tools options

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How to use PCRE s backtracking control verbs to match a line not containing a word  Here s a method that I haven t seen used before      hede  COMMIT       How it works  First  it tries to find  hede  somewhere in the line  If successful  at this point    COMMIT  tells the engine to  not only not backtrack in the event of a failure  but also not to attempt any further matching in that case  Then  we try to match something that cannot possibly match  in this case       If a line does not contain  hede  then the second alternative  an empty subpattern  successfully matches the subject string   This method is no more efficient than a negative lookahead  but I figured I d just throw it on here in case someone finds it nifty and finds a use for it for other  more interesting applications

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Maybe you ll find this on Google while trying to write a regex that is able to match segments of a line  as opposed to entire lines  which do not contain a substring  Tooke me a while to figure out  so I ll share   Given a string     lt span class  good  gt bar lt  span gt  lt span class  bad  gt foo lt  span gt  lt span class  ugly  gt baz lt  span gt    I want to match  lt span gt  tags which do not contain the substring  bad      lt span      bad      gt  will match  lt span class   good   gt  and  lt span class   ugly   gt    Notice that there are two sets  layers  of parentheses    The innermost one is for the negative lookahead  it is not a capture group  The outermost was interpreted by Ruby as capture group but we don t want it to be a capture group  so I added    at it s beginning and it is no longer interpreted as a capture group    Demo in Ruby   s     lt span class  good  gt bar lt  span gt  lt span class  bad  gt foo lt  span gt  lt span class  ugly  gt baz lt  span gt   s scan   lt span      bad      gt        gt     lt span class   good   gt      lt span class   ugly   gt

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Another option is that to add a positive look-ahead and check if hede is anywhere in the input line  then we would negate that  with an expression similar to            bhede b       with word boundaries   The expression is explained on the top right panel of regex101 com  if you wish to explore simplify modify it  and in this link  you can watch how it would match against some sample inputs  if you like   RegEx Circuit jex im visualizes regular expressions

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Benchmarks I decided to evaluate some of the presented Options and compare their performance  as well as use some new Features  Benchmarking on  NET Regex Engine  http   regexhero net tester  Benchmark Text  The first 7 lines should not match  since they contain the searched Expression  while the lower 7 lines should match  Regex Hero is a real-time online Silverlight Regular Expression Tester  XRegex Hero is a real-time online Silverlight Regular Expression Tester  Regex HeroRegex HeroRegex HeroRegex HeroRegex Hero is a real-time online Silverlight Regular Expression Tester  Regex Her Regex Her Regex Her Regex Her Regex Her Regex Her Regex Hero is a real-time online Silverlight Regular Expression Tester  Regex Her is a real-time online Silverlight Regular Expression Tester Regex Hero egex Hero egex Hero egex Hero egex Hero egex Hero egex Hero Regex Hero is a real-time online Silverlight Regular Expression Tester  RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRegex Hero is a real-time online Silverlight Regular Expression Tester   Regex Her egex Hero egex Hero is a real-time online Silverlight Regular Expression Tester  Regex Her is a real-time online Silverlight Regular Expression Tester  Regex Her Regex Her Regex Her Regex Her Regex Her Regex Her is a real-time online Silverlight Regular Expression Tester  Nobody is a real-time online Silverlight Regular Expression Tester  Regex Her o egex Hero Regex  Hero Reg ex Hero is a real-time online Silverlight Regular Expression Tester   Results  Results are Iterations per second as the median of 3 runs - Bigger Number   Better 01       Regex Hero                         3 914      Accepted Answer 02         Regex Hero                       5 034      With Non-Capturing group 03      gt   R   R   egex Hero                 6 137      Lookahead only on the right first letter 04      gt       Regex Hero                    7 426      Match the word and check if you re still at linestart 05           Regex Hero    fail             7 371      Logic Branch  Find Regex Hero  match nothing  else anything  P1           Regex Hero   FAIL    ACCEPT               Logic Branch in Perl - Quick FAIL P2     Regex Hero  COMMIT   FAIL    ACCEPT             Direct COMMIT  amp  FAIL in Perl  Since  NET doesn t support action Verbs   FAIL  etc   I couldn t test the solutions P1 and P2  Summary  I tried to test most proposed solutions  some Optimizations are possible for certain words  For Example if the First two letters of the search string are not the Same  answer 03 can be expanded to     gt   R   R    egex Hero     resulting in a small performance gain  But the overall most readable and performance-wise fastest solution seems to be 05 using a conditional statement or 04 with the possesive quantifier  I think the Perl solutions should be even faster and more easily readable

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The OP did not specify or Tag the post to indicate the context  programming language  editor  tool  the Regex will be used within     For me  I sometimes need to do this while editing a file using Textpad     Textpad supports some Regex  but does not support lookahead or lookbehind  so it takes a few steps     If I am looking to retain all lines that Do NOT contain the string hede  I would do it like this      1  Search replace the entire file to add a unique  Tag  to the beginning of each line containing any text          Search string            Replace string  lt   -unique-   gt  1       Replace-all        2  Delete all lines that contain the string hede  replacement string is empty             Search string  lt   -unique-   gt   hede   n       Replace string  lt nothing gt        Replace-all          3  At this point  all remaining lines Do NOT contain the string hede  Remove the unique  Tag  from all lines  replacement string is empty             Search string  lt   -unique-   gt      Replace string  lt nothing gt        Replace-all     Now you have the original text with all lines containing the string hede removed      If I am looking to Do Something Else to only lines that Do NOT contain the string hede  I would do it like this      1  Search replace the entire file to add a unique  Tag  to the beginning of each line containing any text          Search string            Replace string  lt   -unique-   gt  1       Replace-all        2  For all lines that contain the string hede  remove the unique  Tag             Search string  lt   -unique-   gt    hede      Replace string  1       Replace-all          3  At this point  all lines that begin with the unique  Tag   Do NOT contain the string hede  I can now do my Something Else to only those lines         4  When I am done  I remove the unique  Tag  from all lines  replacement string is empty             Search string  lt   -unique-   gt      Replace string  lt nothing gt        Replace-all

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If you re just using it for grep  you can use grep -v hede to get all lines which do not contain hede   ETA Oh  rereading the question  grep -v is probably what you meant by  tools options

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Note that the solution to does not start with    hede          hede       is generally much more efficient than the solution to does not contain    hede           hede        The former checks for    hede    only at the input string   s first position  rather than at every position

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If you want the regex test to only fail if the entire string matches  the following will work       hede       e g  -- If you want to allow all values except  foo   i e   foofoo    barfoo   and  foobar  will pass  but  foo  will fail   use      foo      Of course  if you re checking for exact equality  a better general solution in this case is to check for string equality  i e    myStr      foo    You could even put the negation outside the test if you need any regex features  here  case insensitivity and range matching        a-f oo  i test myStr    The regex solution at the top of this answer may be helpful  however  in situations where a positive regex test is required  perhaps by an API

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Since no one else has given a direct answer to the question that was asked  I ll do it  The answer is that with POSIX grep  it s impossible to literally satisfy this request  grep  quot  lt Regex for  doesn t contain hede  gt  quot  input  The reason is that POSIX grep is only required to work with Basic Regular Expressions  which are simply not powerful enough for accomplishing that task  they are not capable of parsing all regular languages  because of lack of alternation   However  GNU grep implements extensions that allow it  In particular     is the alternation operator in GNU s implementation of BREs  If your regular expression engine supports alternation  parentheses and the Kleene star  and is able to anchor to the beginning and end of the string  that s all you need for this approach  Note however that negative sets          are very convenient in addition to those  because otherwise  you need to replace them with an expression of the form  a b c        that lists every character that is not in the set  which is extremely tedious and overly long  even more so if the whole character set is Unicode  Thanks to formal language theory  we get to see how such an expression looks like  With GNU grep  the answer would be something like  grep  quot      h   h  h  eh  edh       eh   e  dh   ed  eh          h  h  eh  edh       e  ed      quot  input   found with Grail and some further optimizations made by hand   You can also use a tool that implements Extended Regular Expressions  like egrep  to get rid of the backslashes  egrep  quot     h  h h eh edh     eh  e  dh  ed  eh      h h eh edh    e ed    quot  input  Here s a script to test it  note it generates a file testinput txt in the current directory   Several of the expressions presented fail this test     bin bash REGEX  quot      h   h  h  eh  edh       eh   e  dh   ed  eh          h  h  eh  edh       e  ed      quot     First four lines as in OP s testcase  cat  gt  testinput txt  lt  lt EOF hoho hihi haha hede  h he ah head ahead ahed aheda ahede hhede hehede hedhede hehehehehehedehehe hedecidedthat EOF diff -s -u  lt  grep -v hede testinput txt   lt  grep  quot  REGEX quot  testinput txt   In my system it prints  Files  dev fd 63 and  dev fd 62 are identical  as expected  For those interested in the details  the technique employed is to convert the regular expression that matches the word into a finite automaton  then invert the automaton by changing every acceptance state to non-acceptance and vice versa  and then converting the resulting FA back to a regular expression  As everyone has noted  if your regular expression engine supports negative lookahead  the regular expression is much simpler  For example  with GNU grep  grep -P       hede       input  However  this approach has the disadvantage that it requires a backtracking regular expression engine  This makes it unsuitable in installations that are using secure regular expression engines like RE2  which is one reason to prefer the generated approach in some circumstances  Using Kendall Hopkins  excellent FormalTheory library  written in PHP  which provides a functionality similar to Grail  and a simplifier written by myself  I ve been able to write an online generator of negative regular expressions given an input phrase  only alphanumeric and space characters currently supported   http   www formauri es personal pgimeno misc non-match-regex  For hede it outputs      h  h h e h dh      eh  e   dh  d  eh      h h e h dh    ed        which is equivalent to the above

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As long as you are dealing with lines  simply mark the negative matches and target the rest   In fact  I use this trick with sed because      hede      looks not supported by it   For the desired output   Mark the negative match   e g  lines with hede   using a character not included in the whole text at all  An emoji could probably be a good choice for this purpose   s    hede   1 g  Target the rest  the unmarked strings  e g  lines without hede   Suppose you want to keep only the target and delete the rest  as you want    s      g    For a better understanding  Suppose you want to delete the target    Mark the negative match   e g  lines with hede   using a character not included in the whole text at all  An emoji could probably be a good choice for this purpose   s    hede   1 g  Target the rest  the unmarked strings  e g  lines without hede   Suppose you want to delete the target   s         g  Remove the mark   s   g

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Answer        hede        Explanation    the beginning of the string    group and capture to  1  0 or more times  matching the most amount possible        look ahead to see if there is not     hede your string       end of look-ahead     any character except  n     end of  1    Note  because you are using a quantifier on this capture  only the LAST repetition of the captured pattern will be stored in  1    before an optional  n  and the end of the string

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How to use PCRE s backtracking control verbs to match a line not containing a word  Here s a method that I haven t seen used before      hede  COMMIT       How it works  First  it tries to find  hede  somewhere in the line  If successful  at this point    COMMIT  tells the engine to  not only not backtrack in the event of a failure  but also not to attempt any further matching in that case  Then  we try to match something that cannot possibly match  in this case       If a line does not contain  hede  then the second alternative  an empty subpattern  successfully matches the subject string   This method is no more efficient than a negative lookahead  but I figured I d just throw it on here in case someone finds it nifty and finds a use for it for other  more interesting applications

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Aforementioned       hede     is great because it can be anchored          hede                      A line without hede  foo      hede    bar             foo followed by bar  without hede between them   But the following would suffice in this case         hede                       A line without hede   This simplification is ready to have  AND  clauses added         hede      foo      bar      A line with foo and bar  but without hede       hede      foo   bar         Same

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The TXR Language supports regex negation     txr -c    repeat    nothede   hede     do  put-line nothede     end    Input   A more complicated example  match all lines that start with a and end with z  but do not contain the substring hede     txr -c    repeat    nothede  a  z amp    hede       do  put-line nothede     end   - az          lt - echoed az abcz        lt - echoed abcz abhederz    lt - not echoed  contains hede ahedez      lt - not echoed  contains hede ace         lt - not echoed  does not end in z ahedz       lt - echoed ahedz   Regex negation is not particularly useful on its own but when you also have intersection  things get interesting  since you have a full set of boolean set operations  you can express  the set which matches this  except for things which match that

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With negative lookahead  regular expression can match something not contains specific pattern  This is answered and explained by Bart Kiers  Great explanation   However  with Bart Kiers  answer  the lookahead part will test 1 to 4 characters ahead while matching any single character  We can avoid this and let the lookahead part check out the whole text  ensure there is no  hede   and then the normal part      can eat the whole text all at one time   Here is the improved regex           hede        Note the      lazy quantifier in the negative lookahead part is optional  you can use     greedy quantifier instead  depending on your data  if  hede  does present and in the beginning half of the text  the lazy quantifier can be faster  otherwise  the greedy quantifier be faster  However if  hede  does not present  both would be equal slow   Here is the demo code   For more information about lookahead  please check out the great article  Mastering Lookahead and Lookbehind   Also  please check out RegexGen js  a JavaScript Regular Expression Generator that helps to construct complex regular expressions  With RegexGen js  you can construct the regex in a more readable way   var     regexGen   var regex            startOfLine                       anything   notContains           match anything that not contains            anything   lazy     hede       zero or more chars that followed by  hede                                            i e   anything contains  hede                endOfLine

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Aforementioned       hede     is great because it can be anchored          hede                      A line without hede  foo      hede    bar             foo followed by bar  without hede between them   But the following would suffice in this case         hede                       A line without hede   This simplification is ready to have  AND  clauses added         hede      foo      bar      A line with foo and bar  but without hede       hede      foo   bar         Same

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Here s a good explanation of why it s not easy to negate an arbitrary regex  I have to agree with the other answers  though  if this is anything other than a hypothetical question  then a regex is not the right choice here

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hede      is an elegant solution  except since it consumes characters you won t be able to combine it with other criteria  For instance  say you wanted to check for the non-presence of  hede  and the presence of  haha   This solution would work because it won t consume characters          bhede b       bhaha b

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I wanted to add another example for if you are trying to match an entire line that contains string X  but does not also contain string Y  For example  let s say we want to check if our URL   string contains  quot tasty-treats quot   so long as it does not also contain  quot chocolate quot  anywhere  This regex pattern would work  works in JavaScript too         tasty-treats     chocolate        global  multiline flags in example  Interactive Example  https   regexr com 53gv4 Matches  These urls contain  quot tasty-treats quot  and also do not contain  quot chocolate quot    example com tasty-treats strawberry-ice-cream example com desserts tasty-treats banana-pudding example com tasty-treats-overview  Does Not Match  These urls contain  quot chocolate quot  somewhere - so they won t match even though they contain  quot tasty-treats quot    example com tasty-treats chocolate-cake example com home-cooking oven-roasted-chicken example com tasty-treats banana-chocolate-fudge example com desserts chocolate tasty-treats example com chocolate tasty-treats desserts

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Not regex  but I ve found it logical and useful to use serial greps with pipe to eliminate noise   eg   search an apache config file without all the comments-  grep -v       opt lampp etc httpd conf        this gives all the non-comment lines   and  grep -v       opt lampp etc httpd conf    grep -i dir   The logic of serial grep s is  not a comment  and  matches dir

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Benchmarks I decided to evaluate some of the presented Options and compare their performance  as well as use some new Features  Benchmarking on  NET Regex Engine  http   regexhero net tester  Benchmark Text  The first 7 lines should not match  since they contain the searched Expression  while the lower 7 lines should match  Regex Hero is a real-time online Silverlight Regular Expression Tester  XRegex Hero is a real-time online Silverlight Regular Expression Tester  Regex HeroRegex HeroRegex HeroRegex HeroRegex Hero is a real-time online Silverlight Regular Expression Tester  Regex Her Regex Her Regex Her Regex Her Regex Her Regex Her Regex Hero is a real-time online Silverlight Regular Expression Tester  Regex Her is a real-time online Silverlight Regular Expression Tester Regex Hero egex Hero egex Hero egex Hero egex Hero egex Hero egex Hero Regex Hero is a real-time online Silverlight Regular Expression Tester  RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRegex Hero is a real-time online Silverlight Regular Expression Tester   Regex Her egex Hero egex Hero is a real-time online Silverlight Regular Expression Tester  Regex Her is a real-time online Silverlight Regular Expression Tester  Regex Her Regex Her Regex Her Regex Her Regex Her Regex Her is a real-time online Silverlight Regular Expression Tester  Nobody is a real-time online Silverlight Regular Expression Tester  Regex Her o egex Hero Regex  Hero Reg ex Hero is a real-time online Silverlight Regular Expression Tester   Results  Results are Iterations per second as the median of 3 runs - Bigger Number   Better 01       Regex Hero                         3 914      Accepted Answer 02         Regex Hero                       5 034      With Non-Capturing group 03      gt   R   R   egex Hero                 6 137      Lookahead only on the right first letter 04      gt       Regex Hero                    7 426      Match the word and check if you re still at linestart 05           Regex Hero    fail             7 371      Logic Branch  Find Regex Hero  match nothing  else anything  P1           Regex Hero   FAIL    ACCEPT               Logic Branch in Perl - Quick FAIL P2     Regex Hero  COMMIT   FAIL    ACCEPT             Direct COMMIT  amp  FAIL in Perl  Since  NET doesn t support action Verbs   FAIL  etc   I couldn t test the solutions P1 and P2  Summary  I tried to test most proposed solutions  some Optimizations are possible for certain words  For Example if the First two letters of the search string are not the Same  answer 03 can be expanded to     gt   R   R    egex Hero     resulting in a small performance gain  But the overall most readable and performance-wise fastest solution seems to be 05 using a conditional statement or 04 with the possesive quantifier  I think the Perl solutions should be even faster and more easily readable

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Here s a good explanation of why it s not easy to negate an arbitrary regex  I have to agree with the other answers  though  if this is anything other than a hypothetical question  then a regex is not the right choice here

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Here s a good explanation of why it s not easy to negate an arbitrary regex  I have to agree with the other answers  though  if this is anything other than a hypothetical question  then a regex is not the right choice here

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It may be more maintainable to two regexes in your code  one to do the first match  and then if it matches run the second regex to check for outlier cases you wish to block for example     hede    then have appropriate logic in your code   OK  I admit this is not really an answer to the posted question posted and it may also use slightly more processing than a single regex  But for developers who came here looking for a fast emergency fix for an outlier case then this solution should not be overlooked

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Through PCRE verb   SKIP   F    hede   SKIP   F         This would completely skips the line which contains the exact string hede and matches all the remaining lines   DEMO  Execution of the parts   Let us consider the above regex by splitting it into two parts    Part before the   symbol  Part shouldn t be matched     hede   SKIP   F   Part after the   symbol  Part should be matched            PART 1   Regex engine will start its execution from the first part    hede   SKIP   F    Explanation      Asserts that we are at the start  hede Matches the string hede   Asserts that we are at the line end    So the line which contains the string hede would be matched  Once the regex engine sees the following   SKIP   F   Note  You could write   F  as   FAIL   verb  it skips and make the match to fail    called alteration or logical OR operator added next to the PCRE verb which inturn matches all the boundaries exists between each and every character on all the lines except the line contains the exact string hede  See the demo here  That is  it tries to match the characters from the remaining string  Now the regex in the second part would be executed   PART 2         Explanation       Asserts that we are at the start  ie  it matches all the line starts except the one in the hede line  See the demo here     In the Multiline mode    would match any character except newline or carriage return characters  And   would repeat the previous character zero or more times  So    would match the whole line  See the demo here   Hey why you added    instead of       Because    would match a blank line but    won t match a blank  We want to match all the lines except hede   there may be a possibility of blank lines also in the input   so you must use    instead of         would repeat the previous character one or more times  See    matches a blank line here    End of the line anchor is not necessary here

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Answer        hede        Explanation    the beginning of the string    group and capture to  1  0 or more times  matching the most amount possible        look ahead to see if there is not     hede your string       end of look-ahead     any character except  n     end of  1    Note  because you are using a quantifier on this capture  only the LAST repetition of the captured pattern will be stored in  1    before an optional  n  and the end of the string

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A simpler solution is to use the not operator    Your if statement will need to match  contains  and not match  excludes      var contains    abc   var excludes   hede    if string match contains   amp  amp    string match excludes        proceed      I believe the designers of RegEx anticipated the use of not operators

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If you re just using it for grep  you can use grep -v hede to get all lines which do not contain hede   ETA Oh  rereading the question  grep -v is probably what you meant by  tools options

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FWIW  since regular languages  aka rational languages  are closed under complementation  it s always possible to find a regular expression  aka rational expression  that negates another expression  But not many tools implement this   Vcsn supports this operator  which it denotes  c   postfix    You first define the type of your expressions  labels are letter  lal char  to pick from a to z for instance  defining the alphabet when working with complementation is  of course  very important   and the  value  computed for each word is just a Boolean  true the word is accepted  false  rejected   In Python   In  5   import vcsn         c   vcsn context  lal char a-z   b           c Out 5    a b c d e f g h i j k l m n o p q r s t u v w x y z       then you enter your expression   In  6   e   c expression   hede  c     e Out 6    hede  c   convert this expression to an automaton   In  7   a   e automaton    a     finally  convert this automaton back to a simple expression   In  8   print a expression             e h  e e  e d      h  h   e  e   d  d   e  e              where   is usually denoted     e denotes the empty word  and     is usually written    any character    So  with a bit of rewriting    h ed       h  h   e  e   d  d   e  e          You can see this example here  and try Vcsn online there

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An  in my opinon  more readable variant of the top answer          hede    Basically   match at the beginning of the line if and only if it does not have  hede  in it  - so the requirement translated almost directly into regex   Of course  it s possible to have multiple failure requirements          hede hodo hada     Details  The   anchor ensures the regex engine doesn t retry the match at every location in the string  which would match every string   The   anchor in the beginning is meant to represent the beginning of the line  The grep tool matches each line one at a time  in contexts where you re working with a multiline string  you can use the  m  flag          hede  m   JavaScript syntax   or    m       hede    Inline flag

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Another option is that to add a positive look-ahead and check if hede is anywhere in the input line  then we would negate that  with an expression similar to            bhede b       with word boundaries   The expression is explained on the top right panel of regex101 com  if you wish to explore simplify modify it  and in this link  you can watch how it would match against some sample inputs  if you like   RegEx Circuit jex im visualizes regular expressions

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Since the introduction of ruby-2 4 1  we can use the new Absent Operator in Ruby   s Regular Expressions  from the official doc     abc  matches       ab    aab    cccc   etc  It doesn t match   abc    aabc    ccccabc   etc    Thus  in your case     hede   does the job for you  2 4 1  016  gt    hoho    hihi    haha    hede   select  s       hede    match s      gt    hoho    hihi    haha

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Here s how I d do it      h   h   ede   h        Accurate and more efficient than the other answers  It implements Friedl s  unrolling-the-loop  efficiency technique and requires much less backtracking

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With ConyEdit  you can use the command line cc gl   hede  to get lines that do not contain the regex matching  or use the command line cc dl  hede  to delete lines that contain the regex matching  They have the same result

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If you want to match a character to negate a word similar to negate character class   For example  a string    lt    str  aaa        bbb4      aaa     bbb7     gt    Do not use    lt   preg match   aaa  bbb   bbb7 s    str   matches     gt    Use    lt   preg match   aaa      bbb     bbb7 s    str   matches     gt    Notice     bbb    is neither lookbehind nor lookahead  it s lookcurrent  for example       abc abcde       abc abcde

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Through PCRE verb   SKIP   F    hede   SKIP   F         This would completely skips the line which contains the exact string hede and matches all the remaining lines   DEMO  Execution of the parts   Let us consider the above regex by splitting it into two parts    Part before the   symbol  Part shouldn t be matched     hede   SKIP   F   Part after the   symbol  Part should be matched            PART 1   Regex engine will start its execution from the first part    hede   SKIP   F    Explanation      Asserts that we are at the start  hede Matches the string hede   Asserts that we are at the line end    So the line which contains the string hede would be matched  Once the regex engine sees the following   SKIP   F   Note  You could write   F  as   FAIL   verb  it skips and make the match to fail    called alteration or logical OR operator added next to the PCRE verb which inturn matches all the boundaries exists between each and every character on all the lines except the line contains the exact string hede  See the demo here  That is  it tries to match the characters from the remaining string  Now the regex in the second part would be executed   PART 2         Explanation       Asserts that we are at the start  ie  it matches all the line starts except the one in the hede line  See the demo here     In the Multiline mode    would match any character except newline or carriage return characters  And   would repeat the previous character zero or more times  So    would match the whole line  See the demo here   Hey why you added    instead of       Because    would match a blank line but    won t match a blank  We want to match all the lines except hede   there may be a possibility of blank lines also in the input   so you must use    instead of         would repeat the previous character one or more times  See    matches a blank line here    End of the line anchor is not necessary here

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Not regex  but I ve found it logical and useful to use serial greps with pipe to eliminate noise   eg   search an apache config file without all the comments-  grep -v       opt lampp etc httpd conf        this gives all the non-comment lines   and  grep -v       opt lampp etc httpd conf    grep -i dir   The logic of serial grep s is  not a comment  and  matches dir

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I wanted to add another example for if you are trying to match an entire line that contains string X  but does not also contain string Y  For example  let s say we want to check if our URL   string contains  quot tasty-treats quot   so long as it does not also contain  quot chocolate quot  anywhere  This regex pattern would work  works in JavaScript too         tasty-treats     chocolate        global  multiline flags in example  Interactive Example  https   regexr com 53gv4 Matches  These urls contain  quot tasty-treats quot  and also do not contain  quot chocolate quot    example com tasty-treats strawberry-ice-cream example com desserts tasty-treats banana-pudding example com tasty-treats-overview  Does Not Match  These urls contain  quot chocolate quot  somewhere - so they won t match even though they contain  quot tasty-treats quot    example com tasty-treats chocolate-cake example com home-cooking oven-roasted-chicken example com tasty-treats banana-chocolate-fudge example com desserts chocolate tasty-treats example com chocolate tasty-treats desserts

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The OP did not specify or Tag the post to indicate the context  programming language  editor  tool  the Regex will be used within     For me  I sometimes need to do this while editing a file using Textpad     Textpad supports some Regex  but does not support lookahead or lookbehind  so it takes a few steps     If I am looking to retain all lines that Do NOT contain the string hede  I would do it like this      1  Search replace the entire file to add a unique  Tag  to the beginning of each line containing any text          Search string            Replace string  lt   -unique-   gt  1       Replace-all        2  Delete all lines that contain the string hede  replacement string is empty             Search string  lt   -unique-   gt   hede   n       Replace string  lt nothing gt        Replace-all          3  At this point  all remaining lines Do NOT contain the string hede  Remove the unique  Tag  from all lines  replacement string is empty             Search string  lt   -unique-   gt      Replace string  lt nothing gt        Replace-all     Now you have the original text with all lines containing the string hede removed      If I am looking to Do Something Else to only lines that Do NOT contain the string hede  I would do it like this      1  Search replace the entire file to add a unique  Tag  to the beginning of each line containing any text          Search string            Replace string  lt   -unique-   gt  1       Replace-all        2  For all lines that contain the string hede  remove the unique  Tag             Search string  lt   -unique-   gt    hede      Replace string  1       Replace-all          3  At this point  all lines that begin with the unique  Tag   Do NOT contain the string hede  I can now do my Something Else to only those lines         4  When I am done  I remove the unique  Tag  from all lines  replacement string is empty             Search string  lt   -unique-   gt      Replace string  lt nothing gt        Replace-all

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The TXR Language supports regex negation     txr -c    repeat    nothede   hede     do  put-line nothede     end    Input   A more complicated example  match all lines that start with a and end with z  but do not contain the substring hede     txr -c    repeat    nothede  a  z amp    hede       do  put-line nothede     end   - az          lt - echoed az abcz        lt - echoed abcz abhederz    lt - not echoed  contains hede ahedez      lt - not echoed  contains hede ace         lt - not echoed  does not end in z ahedz       lt - echoed ahedz   Regex negation is not particularly useful on its own but when you also have intersection  things get interesting  since you have a full set of boolean set operations  you can express  the set which matches this  except for things which match that

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With negative lookahead  regular expression can match something not contains specific pattern  This is answered and explained by Bart Kiers  Great explanation   However  with Bart Kiers  answer  the lookahead part will test 1 to 4 characters ahead while matching any single character  We can avoid this and let the lookahead part check out the whole text  ensure there is no  hede   and then the normal part      can eat the whole text all at one time   Here is the improved regex           hede        Note the      lazy quantifier in the negative lookahead part is optional  you can use     greedy quantifier instead  depending on your data  if  hede  does present and in the beginning half of the text  the lazy quantifier can be faster  otherwise  the greedy quantifier be faster  However if  hede  does not present  both would be equal slow   Here is the demo code   For more information about lookahead  please check out the great article  Mastering Lookahead and Lookbehind   Also  please check out RegexGen js  a JavaScript Regular Expression Generator that helps to construct complex regular expressions  With RegexGen js  you can construct the regex in a more readable way   var     regexGen   var regex            startOfLine                       anything   notContains           match anything that not contains            anything   lazy     hede       zero or more chars that followed by  hede                                            i e   anything contains  hede                endOfLine

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FWIW  since regular languages  aka rational languages  are closed under complementation  it s always possible to find a regular expression  aka rational expression  that negates another expression  But not many tools implement this   Vcsn supports this operator  which it denotes  c   postfix    You first define the type of your expressions  labels are letter  lal char  to pick from a to z for instance  defining the alphabet when working with complementation is  of course  very important   and the  value  computed for each word is just a Boolean  true the word is accepted  false  rejected   In Python   In  5   import vcsn         c   vcsn context  lal char a-z   b           c Out 5    a b c d e f g h i j k l m n o p q r s t u v w x y z       then you enter your expression   In  6   e   c expression   hede  c     e Out 6    hede  c   convert this expression to an automaton   In  7   a   e automaton    a     finally  convert this automaton back to a simple expression   In  8   print a expression             e h  e e  e d      h  h   e  e   d  d   e  e              where   is usually denoted     e denotes the empty word  and     is usually written    any character    So  with a bit of rewriting    h ed       h  h   e  e   d  d   e  e          You can see this example here  and try Vcsn online there

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Note that the solution to does not start with    hede          hede       is generally much more efficient than the solution to does not contain    hede           hede        The former checks for    hede    only at the input string   s first position  rather than at every position

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with this  you avoid to test a lookahead on each positions          h   h     ede         equivalent to  for  net        gt      h   h    ede        Old answer        gt   h   h    ede

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with this  you avoid to test a lookahead on each positions          h   h     ede         equivalent to  for  net        gt      h   h    ede        Old answer        gt   h   h    ede

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It may be more maintainable to two regexes in your code  one to do the first match  and then if it matches run the second regex to check for outlier cases you wish to block for example     hede    then have appropriate logic in your code   OK  I admit this is not really an answer to the posted question posted and it may also use slightly more processing than a single regex  But for developers who came here looking for a fast emergency fix for an outlier case then this solution should not be overlooked

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Here s how I d do it      h   h   ede   h        Accurate and more efficient than the other answers  It implements Friedl s  unrolling-the-loop  efficiency technique and requires much less backtracking

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Here s a good explanation of why it s not easy to negate an arbitrary regex  I have to agree with the other answers  though  if this is anything other than a hypothetical question  then a regex is not the right choice here

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With ConyEdit  you can use the command line cc gl   hede  to get lines that do not contain the regex matching  or use the command line cc dl  hede  to delete lines that contain the regex matching  They have the same result

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If you want the regex test to only fail if the entire string matches  the following will work       hede       e g  -- If you want to allow all values except  foo   i e   foofoo    barfoo   and  foobar  will pass  but  foo  will fail   use      foo      Of course  if you re checking for exact equality  a better general solution in this case is to check for string equality  i e    myStr      foo    You could even put the negation outside the test if you need any regex features  here  case insensitivity and range matching        a-f oo  i test myStr    The regex solution at the top of this answer may be helpful  however  in situations where a positive regex test is required  perhaps by an API

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An  in my opinon  more readable variant of the top answer          hede    Basically   match at the beginning of the line if and only if it does not have  hede  in it  - so the requirement translated almost directly into regex   Of course  it s possible to have multiple failure requirements          hede hodo hada     Details  The   anchor ensures the regex engine doesn t retry the match at every location in the string  which would match every string   The   anchor in the beginning is meant to represent the beginning of the line  The grep tool matches each line one at a time  in contexts where you re working with a multiline string  you can use the  m  flag          hede  m   JavaScript syntax   or    m       hede    Inline flag

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The given answers are perfectly fine  just an academic point   Regular Expressions in the meaning of theoretical computer sciences ARE NOT ABLE do it like this  For them it had to look something like this       h       h   e          he   h          heh   e          hehe        This only does a FULL match  Doing it for sub-matches would even be more awkward

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As long as you are dealing with lines  simply mark the negative matches and target the rest   In fact  I use this trick with sed because      hede      looks not supported by it   For the desired output   Mark the negative match   e g  lines with hede   using a character not included in the whole text at all  An emoji could probably be a good choice for this purpose   s    hede   1 g  Target the rest  the unmarked strings  e g  lines without hede   Suppose you want to keep only the target and delete the rest  as you want    s      g    For a better understanding  Suppose you want to delete the target    Mark the negative match   e g  lines with hede   using a character not included in the whole text at all  An emoji could probably be a good choice for this purpose   s    hede   1 g  Target the rest  the unmarked strings  e g  lines without hede   Suppose you want to delete the target   s         g  Remove the mark   s   g

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hede      is an elegant solution  except since it consumes characters you won t be able to combine it with other criteria  For instance  say you wanted to check for the non-presence of  hede  and the presence of  haha   This solution would work because it won t consume characters          bhede b       bhaha b

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The given answers are perfectly fine  just an academic point   Regular Expressions in the meaning of theoretical computer sciences ARE NOT ABLE do it like this  For them it had to look something like this       h       h   e          he   h          heh   e          hehe        This only does a FULL match  Doing it for sub-matches would even be more awkward

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If you want to match a character to negate a word similar to negate character class   For example  a string    lt    str  aaa        bbb4      aaa     bbb7     gt    Do not use    lt   preg match   aaa  bbb   bbb7 s    str   matches     gt    Use    lt   preg match   aaa      bbb     bbb7 s    str   matches     gt    Notice     bbb    is neither lookbehind nor lookahead  it s lookcurrent  for example       abc abcde       abc abcde

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The below function will help you get your desired output   lt  PHP       function removePrepositions  text                 propositions array    bfor b i     bthe b i                  if  count  propositions   gt  0                     foreach  propositions as  exceptionPhrase                         text   preg replace  exceptionPhrase      trim  text                                    retval   trim  text                          return  retval            gt

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Since no one else has given a direct answer to the question that was asked  I ll do it  The answer is that with POSIX grep  it s impossible to literally satisfy this request  grep  quot  lt Regex for  doesn t contain hede  gt  quot  input  The reason is that POSIX grep is only required to work with Basic Regular Expressions  which are simply not powerful enough for accomplishing that task  they are not capable of parsing all regular languages  because of lack of alternation   However  GNU grep implements extensions that allow it  In particular     is the alternation operator in GNU s implementation of BREs  If your regular expression engine supports alternation  parentheses and the Kleene star  and is able to anchor to the beginning and end of the string  that s all you need for this approach  Note however that negative sets          are very convenient in addition to those  because otherwise  you need to replace them with an expression of the form  a b c        that lists every character that is not in the set  which is extremely tedious and overly long  even more so if the whole character set is Unicode  Thanks to formal language theory  we get to see how such an expression looks like  With GNU grep  the answer would be something like  grep  quot      h   h  h  eh  edh       eh   e  dh   ed  eh          h  h  eh  edh       e  ed      quot  input   found with Grail and some further optimizations made by hand   You can also use a tool that implements Extended Regular Expressions  like egrep  to get rid of the backslashes  egrep  quot     h  h h eh edh     eh  e  dh  ed  eh      h h eh edh    e ed    quot  input  Here s a script to test it  note it generates a file testinput txt in the current directory   Several of the expressions presented fail this test     bin bash REGEX  quot      h   h  h  eh  edh       eh   e  dh   ed  eh          h  h  eh  edh       e  ed      quot     First four lines as in OP s testcase  cat  gt  testinput txt  lt  lt EOF hoho hihi haha hede  h he ah head ahead ahed aheda ahede hhede hehede hedhede hehehehehehedehehe hedecidedthat EOF diff -s -u  lt  grep -v hede testinput txt   lt  grep  quot  REGEX quot  testinput txt   In my system it prints  Files  dev fd 63 and  dev fd 62 are identical  as expected  For those interested in the details  the technique employed is to convert the regular expression that matches the word into a finite automaton  then invert the automaton by changing every acceptance state to non-acceptance and vice versa  and then converting the resulting FA back to a regular expression  As everyone has noted  if your regular expression engine supports negative lookahead  the regular expression is much simpler  For example  with GNU grep  grep -P       hede       input  However  this approach has the disadvantage that it requires a backtracking regular expression engine  This makes it unsuitable in installations that are using secure regular expression engines like RE2  which is one reason to prefer the generated approach in some circumstances  Using Kendall Hopkins  excellent FormalTheory library  written in PHP  which provides a functionality similar to Grail  and a simplifier written by myself  I ve been able to write an online generator of negative regular expressions given an input phrase  only alphanumeric and space characters currently supported   http   www formauri es personal pgimeno misc non-match-regex  For hede it outputs      h  h h e h dh      eh  e   dh  d  eh      h h e h dh    ed        which is equivalent to the above

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If you re just using it for grep  you can use grep -v hede to get all lines which do not contain hede   ETA Oh  rereading the question  grep -v is probably what you meant by  tools options

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The below function will help you get your desired output   lt  PHP       function removePrepositions  text                 propositions array    bfor b i     bthe b i                  if  count  propositions   gt  0                     foreach  propositions as  exceptionPhrase                         text   preg replace  exceptionPhrase      trim  text                                    retval   trim  text                          return  retval            gt

[regex] Regular expression to match a line that doesn't contain a word

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