nclean

nclean is essentially a filtering tool. It iterates over stdin and prints all lines that meet your specified criteria of length and charset.

For example, with the following command

$ cat words.txt | nclean -c

where words.txt contains the following:

pen
Pen
pencil
Pencil
eraser
Eraser

The program will output this:

Pen
Pencil
Eraser

Because the -c flag filters out lines that have capital letters and prints those out only.

Likewise:

With the -n flag, the program will only print lines that include numbers;
With the -s flag, the program will only print lines that include symbols and special characters;
With the -l flag, the program will only print lines with length grater than or equal to the one specified;

You can, of course, combine different options in a single command

νάρθηξ - narthex