How to search for strings that occur more than once in a line?

Question

I know that I can use grep to search for a string. But what if I want the output to show only lines where the string I search for occurred more than once? I prefer grep.

To clarify, I need to print the lines where the keyword appears more than once (i.e. two or above, or at least two). But I do not mean the lines that have exactly two.

Answer 1

If the search string can occur anywhere on the line, you could could do grep 'str.*str' for at least two matches.

And if you want to match the string multiple times, e.g. at least three times, you could do grep '\(.*str\)\{3\}'.

Answer 2

So, you need to match lines that have an string (at least) "two times".

1. That's (with backreferences):

   $ str="string to match";     grep '\('"$str"'\).*\1' file
   

   Assuming that str is an string that avoids regex structures (or they are correctly quoted to avoid them being interpreted as a regex). Of course, str could be a regex, but it will match an string, the first one, and check for repeats of that string, not generic regexes. That is: str=h[aeiou]t will not match aaa hot bbb hit cccc, only hit bbb hit.

2. Or (with generic regexes (probably faster)):

   str="string or regex to match";       grep '\(.*'"$str"'\)\{2\}' file
   

   where the number 2 could be replaced by any count easily (four or more here):

   str="regex to match"; n=4;            grep '\(.*'"$str"'\)\{'"$n"'\}' file
   

   That is: this will match hat het hit hot hut or hat hat hat hat

   str='h[aeiou]t'; n=4;                 grep '\(.*'"$str"'\)\{'"$n"'\}' file
   

Answer 3

It's impossible to search for 2 or more occurrences of a string in a line using grep since you'd need to use regexp constructs to join the "strings" and then the strings are no longer strings, they're regexps. You need to use awk instead, e.g. to find 2 or more ocurrences of the string .*:

$ echo 'foo.*bar' | awk -v str='.*' '(s=index($0,str)) && index(substr($0,s+length(str)),str)'
$
$ echo 'foo.*bar.*etc' | awk -v str='.*' '(s=index($0,str)) && index(substr($0,s+length(str)),str)'
foo.*bar.*etc