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--- remove_lines_with_duplicate_letters [2023/08/11 14:40] – ↷ Page name changed from remove_lines_duplicate_letters to remove_lines_with_duplicate_letters raju
+++ remove_lines_with_duplicate_letters [2023/08/27 23:48] (current) – raju
@@ Line 3: / Line 3: @@
 Find five letter words that are made up of letters {h, i, k, e, r, s} where each letter appears only once.
 ==== Issue ====
-If we do
 <code>
-grep -i "^[hikers][hikers][hikers][hikers][hikers]$" /usr/share/dict/american-english
+grep -Ei "^[hikers]{5}$" /usr/share/dict/american-english
-<code>
+</code>
-shows
+gives
 <code>
 Essie
@@ Line 17: / Line 16: @@
 ...
 </code>
-some of the words have the letters duplicated. For example, in 'Irish' the letter 'i' is repeated twice. Such words should be filtered out.
+where some letters are duplicated in some of the words. For example, the letter 'i' appears twice in the word 'Irish'. We need to filter out all such words.
 ==== 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.