repeat string in a line using sed

Question

I would like to repeat each line's content of a file, any quick solution using sed.

supposed the input file is

abc
def
123

The expected ouput is:

abcabc
defdef
123123

Answer 1

sed 's \(.*\) \1\1 ' infile

Answer 2

This might work for you:

echo -e 'aaA\nbbB\nccC' | sed 's/.*/&&/'
aaAaaA
bbBbbB
ccCccC

Answer 3

sed 'h;G;s/\n//' file.txt

Answer 4

It's even simpler if you take advantage of the variable \0, which holds the string that was matched:

sed 's/.*/\0\0/'