grep : Find occurances of 3 consecutive alphabets

Question

I want to find aaa, bbb etc I've tried :

grep -E [a-z]\{3\} 1.txt

but this even prints abc

Answer 1

You can use references to capturing groups:

[/tmp] cat test.txt                                                            
aaa
bbb
abc
aab
bbc
[/tmp] grep -E "([a-z])\1{2}" test.txt                                         
aaa
bbb

\1 refers to the stuff captured by ([a-z]) (a single letter, in your case), so the regex looks for a single letter followed by the same letter two more times.