Regular expression to find two strings anywhere in input

Question

How do I write a regular expression to match two given strings  at any position in the string   For example  if I am searching for cat and mat  it should match   The cat slept on the mat in front of the fire  At 5 00 pm  I found the cat scratching the wool off the mat    No matter what precedes these strings

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You can try    bcat b   bmat b    b is an anchor and matches a word boundary  It will look for words cat and mat anywhere in the string with mat following cat  It will not match   Therez caterpillar on the mat    but will match   The cat slept on the mat in front of the fire  If you want to match strings which have letters cat followed by mat  you can try   cat  mat   This will match both the above example strings

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This is fairly easy on processing power required    string1    n  string2   string2    n  string1   I used this in visual studio 2013 to find all files that had both string 1 and 2 in it

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word1   word2         word2   word1

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you don t have to use regex  In your favourite language  split on spaces  go over the splitted words  check for cat and mat  eg in Python   gt  gt  gt  for line in open  file            g 0 f 0         s   line split           for item in s              if item    cat   f 1             if item    mat   g 1         if  g f    1 1   print  found     line rstrip    found   The cat slept on the mat in front of the fire  found   At 5 00 pm  I found the cat scratching the wool off the mat

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bcat b    bmat b     m   Using the m modifier  which ensures the beginning end metacharacters match on line breaks rather than at the very beginning and end of the string       matches the line beginning     matches anything on the line before     b matches a word boundary the first occurrence of a word boundary  as  codaddict discussed  then the string cat and another word boundary  note that underscores are treated as  word  characters  so  cat  would not match        any characters before    boundary  mat  boundary      any remaining characters before       the end of the line    It s important to use  b to ensure the specified words aren t part of longer words  and it s important to use non-greedy wildcards       versus greedy      because the latter would fail on strings like  There is a cat on top of the mat which is under the cat    It would match the last occurrence of  cat  rather than the first      If you want to be able to match  cat   you can use            b   cat    b          b   mat    b        m   which matches either underscores or word boundaries around the specified words       indicates a non-capturing group  which can help with performance or avoid conflicted captures   Edit  A question was raised in the comments about whether the solution would work for phrases rather than just words  The answer is  absolutely yes  The following would match  A line which includes both the first phrase and the second phrase             b   first phrase here    b          b   second phrase here    b        m   Edit 2  If order doesn t matter you can use            b    first    b          b   second second    b          b   first     b        m   And if performance is really an issue here  it s possible lookaround  if your regex engine supports it  might  but probably won t  perform better than the above  but I ll leave both the arguably more complex lookaround version and performance testing as an exercise to the questioner reader   Edited per  Alan Moore s comment  I didn t have a chance to test it  but I ll take your word for it

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This works for searching files that contain both String1 and String2       n   String1     n   String2        n   String2     n   String1   Match any number of characters or line fields followed by String1 followed by any number of characters or line fields followed by String2 OR Match any number of characters or line fields followed by String2 followed by any number of characters or line fields followed by String1

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If you absolutely need to only use one regex then           string1         string2   is   i modifier   case-insensitive      Lazy evaluation for any character  matches as few as possible       for Positive LookAhead it has to match somewhere  s modifier     period  also accepts line breaks

[regex] Regular expression to find two strings anywhere in input

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