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--- remove_lines_with_duplicate_letters [2023/08/11 14:43] – raju
+++ remove_lines_with_duplicate_letters [2023/08/27 23:48] (current) – raju
@@ Line 4: / Line 4: @@
 ==== Issue ====
 <code>
-grep -i "^[hikers][hikers][hikers][hikers][hikers]$" /usr/share/dict/american-english
+grep -Ei "^[hikers]{5}$" /usr/share/dict/american-english
 </code>
 gives
@@ Line 19: / Line 19: @@
 ==== Solution ====
+Pipe the output to ''grep -viE '(.).*\1' ''. For example
 <code>
- % grep -i "^[hikers][hikers][hikers][hikers][hikers]$" /usr/share/dict/american-english | grep -viE '(.).*\1'
+% grep -Ei "^[hikers]{5}$" /usr/share/dict/american-english | grep -viE "(.).*\1"
 Sheri
 Shrek
@@ Line 32: / Line 34: @@
 skier
 </code>
+==== Ref ====
+  * https://unix.stackexchange.com/questions/352927/delete-all-lines-that-contain-duplicate-letters -> comment by Stéphane Chazelas
+    * I got the idea from here.
+  * (Mastering Regular Expressions, Jeffrey E.F. Friedl, 2006) book -> Chapter 1 "Introduction to Regular Expressions" -> section "Parentheses and Backreferences" -> pages 20 through 22 go over this concept.