==== dummy ====
  * [[Remove lines with duplicate letters]]
  * [[grep on find results]]

==== wordscapes ====
tags | word scape, wordscape
<code>
% grep -i "^[slev][slev][slev][slev]s$" /usr/share/dict/american-english 
elves
sells
</code>

Remove lines with duplicate letters
<code>
 % grep -Ei "^[hikers]{5}$" /usr/share/dict/american-english | grep -Eiv "(.).*\1"
...
shire
shirk
skier
</code>

compare this with
<code>
 % grep -Ei "^[hikers]{5}$" /usr/share/dict/american-english
...
shire
shirk
shirr
sires
sises
skier
skies
</code>

which also shows words where some letters are repeated twice.

==== repeat previous character N times ====
Use (character){N} and call grep with -E

<code>
 % grep -Ei "^[enrich]i([enrich]){2}e$" /usr/share/dict/american-english
Circe
niche
niece
</code>

is equivalent to
<code>
 % grep -i "^[enrich]i[enrich][enrich]e$" /usr/share/dict/american-english
Circe
niche
niece
</code>

Another example:
<code>
 % grep -Ei "^([dunes]){2}u([dunes]){2}d$" /usr/share/dict/american-english
unused
</code>

==== print lines with less than a certain number of characters ====
To print lines that contain less than N characters
<code>
grep -Ev ".{N}" data.txt
</code>

For example:
To print lines that contain less then 6 characters
<code>
grep -Ev ".{6}" data.txt
</code>

You can also do
<code>
grep -v "......" data.txt
</code>
where the . is repeated N times. This is easier to type for small N.

Sample run:
<code>
$ cat data.txt
a
ab
abc
abcd
abcde
abcdef
abcdefg

$ grep -v "......" data.txt
a
ab
abc
abcd
abcde

$ grep -Ev ".{6}" data.txt
a
ab
abc
abcd
abcde
</code>