¿Cómo puedo usar las expresiones regulares lookahead y lookbehind en Linux usando find?

find (tanto las variantes GNU como BSD) no son compatibles con lookahead/lookbehind. GNU grep solo admite las variantes de expresiones regulares básicas y extendidas de POSIX, así como un par de otras.

Lookahead y lookbehind son elementos de expresiones regulares de estilo Perl, por lo que tendría que usar Perl directamente o GNU grep con el -P opción, que luego interpreta Perl regex.

use la expresión regular de una sola línea de perl pasando la salida de búsqueda con una canalización. Utilicé lookbehind (obtener origen enlaces en html) y lookahead para " y le pasó la salida de curl (html).

bash-3.2# curl stackoverflow.com | perl -0777 -ne '$a=1;while(m/(?<=src\=\")(.*)(?=\")/g){print "Match #".$a." "."$&\n";$a+=1;}'
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  239k  100  239k    0     0  1911k      0 --:--:-- --:--:-- --:--:-- 1919k
Match #1 //ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js
Match #2 //cdn.sstatic.net/Js/stub.en.js?v=fb6157e02696
Match #3 https://ssum-sec.casalemedia.com/usermatch?s=183712&amp;cb=https%3A%2F%2Fengine.adzerk.net%2Fudb%2F22%2Fsync%2Fi.gif%3FpartnerId%3D1%26userId%3D
Match #4 //i.stack.imgur.com/817gJ.png" height="16" width="18" alt="" class="sponsor-tag-img">elasticsearch</a> <a href="/questions/tagged/elasticsearch-2.0" class="post-tag" title="show questions tagged &#39;elasticsearch-2.0&#39;" rel="tag">elasticsearch-2.0</a> <a href="/questions/tagged/elasticsearch-dsl" class="post-tag" title="show questions tagged &#39;elasticsearch-dsl&#39;" rel="tag
Match #5 //i.stack.imgur.com/817gJ.png" height="16" width="18" alt="" class="sponsor-tag-img">elasticsearch</a> <a href="/questions/tagged/sharding" class="post-tag" title="show questions tagged &#39;sharding&#39;" rel="tag">sharding</a> <a href="/questions/tagged/master" class="post-tag" title="show questions tagged &#39;master&#39;" rel="tag
Match #6 //i.stack.imgur.com/tKsDb.png" height="16" width="18" alt="" class="sponsor-tag-img">android</a> <a href="/questions/tagged/linux" class="post-tag" title="show questions tagged &#39;linux&#39;" rel="tag">linux</a> <a href="/questions/tagged/camera" class="post-tag" title="show questions tagged &#39;camera&#39;" rel="tag
Match #7 //i.stack.imgur.com/tKsDb.png" height="16" width="18" alt="" class="sponsor-tag-img">android</a> <a href="/questions/tagged/firebase" class="post-tag" title="show questions tagged &#39;firebase&#39;" rel="tag"><img src="//i.stack.imgur.com/5d55j.png" height="16" width="18" alt="" class="sponsor-tag-img">firebase</a> <a href="/questions/tagged/firebase-authentication" class="post-tag" title="show questions tagged &#39;firebase-authentication&#39;" rel="tag
Match #8 //i.stack.imgur.com/tKsDb.png" height="16" width="18" alt="" class="sponsor-tag-img">android</a> <a href="/questions/tagged/ios" class="post-tag" title="show questions tagged &#39;ios&#39;" rel="tag">ios</a> <a href="/questions/tagged/in-app-purchase" class="post-tag" title="show questions tagged &#39;in-app-purchase&#39;" rel="tag">in-app-purchase</a> <a href="/questions/tagged/piracy-protection" class="post-tag" title="show questions tagged &#39;piracy-protection&#39;" rel="tag
Match #9 //i.stack.imgur.com/tKsDb.png" height="16" width="18" alt="" class="sponsor-tag-img">android</a> <a href="/questions/tagged/unity3d" class="post-tag" title="show questions tagged &#39;unity3d&#39;" rel="tag">unity3d</a> <a href="/questions/tagged/vr" class="post-tag" title="show questions tagged &#39;vr&#39;" rel="tag
Match #10 http://pixel.quantserve.com/pixel/p-c1rF4kxgLUzNc.gif" alt="" class="dno
bash-3.2# date
Mon Oct 24 20:57:11 EDT 2016