For example, I have a string like this:
Line 1
<br/>
<br/>
Line 2
<br/>
<br/>
<br/>
Line 3
I need to detect and replace the duplicated and attached string like the <br/>'s so it will be only 1 <br/> instead. So the final result I expect is:
Line 1
<br/>
Line 2
<br/>
Line 3
Anyone can help me with the regex? explanation will be appreciated.
preg_replace('/(.{3,})\\1+/s', '\\1', $string);
This will replace any sequence of duplicate strings of 3 chars or more.
Try it here: http://ideone.com/5ew7X
If you want to replace only the <br/>s:
preg_replace('/(<br\/>\s*){2,}/s', '\\1', $string);
Not the straight answer to your regex question, still consider doing it using sed; courtesy of Eric Pement's sed one-liners.
# delete duplicate, consecutive lines from a file (emulates "uniq").
# First line in a set of duplicate lines is kept, rest are deleted.
sed '$!N; /^\(.*\)\n\1$/!P; D'
# delete duplicate, nonconsecutive lines from a file. Beware not to
# overflow the buffer size of the hold space, or else use GNU sed.
sed -n 'G; s/\n/&&/; /^\([ -~]*\n\).*\n\1/d; s/\n//; h; P'
# delete all lines except duplicate lines (emulates "uniq -d").
sed '$!N; s/^\(.*\)\n\1$/\1/; t; D'
